Emission Control Systems — 1996 Jeep Grand Cherokee ZJ Service Manual

Pages 1485–1505 · 21 pages · 19 words repaired

detected, the PCM sends a message to the instrument cluster to illuminate the lamp. The PCM illuminates the MIL only for DTC’s that affect vehicle emissions. There are some monitors that may take two consecutive trips, with a detected fault, before the MIL is illuminated. The MIL stays on continuously when the PCM has entered a Limp-In mode or identified a failed emission component. Refer to the Diagnostic Trouble Code charts in this group for emission related codes.

Also, the MIL either flashes or illuminates continuously when the PCM detects active engine misfire. Refer to Misfire Monitoring in this section.

Additionally, the PCM may reset (turn off) the MIL when one of the following occur:

• PCM does not detect the malfunction for 3 consecutive trips (except misfire and Fuel system Monitors).

• PCM does not detect a malfunction while performing three successive engine misfire or fuel system tests. The PCM performs these tests while the engine is operating within 6 375 RPM of and within 10 % of the load of the operating condition at which the malfunction was first detected.

STATE DISPLAY TEST MODE

The switch inputs to the Powertrain Control Module (PCM) have two recognized states; HIGH and LOW. For this reason, the PCM cannot recognize the difference between a selected switch position versus an open circuit, a short circuit, or a defective switch. If the State Display screen shows the change from HIGH to LOW or LOW to HIGH, assume the entire switch circuit to the PCM functions properly. Connect the DRB scan tool to the data link connector and access the state display screen. Then access either

State Display Inputs and Outputs or State Display Sensors.

CIRCUIT ACTUATION TEST MODE

The Circuit Actuation Test Mode checks for proper operation of output circuits or devices the Powertrain Control Module (PCM) may not internally recognize. The PCM attempts to activate these outputs and allow an observer to verify proper operation. Most of the tests provide an audible or visual indication of device operation (click of relay contacts, fuel spray, etc.). Except for intermittent conditions, if a device functions properly during testing, assume the device, its associated wiring, and driver circuit work correctly. Connect the DRB scan tool to the data link connector and access the Actuators screen.

DIAGNOSTIC TROUBLE CODES

A Diagnostic Trouble Code (DTC) indicates the PCM has recognized an abnormal condition in the system.

The technician can display a DTC in three different ways:

• a two-digit number flashed on the Malfunction Indicator (Check Engine) Lamp

• a two-digit number displayed on the vehicle odometer

• a description of the DTC can be read using the DRB scan tool

Diagnostic trouble codes are the results of a system or circuit failure, but do not directly identify the failed component or components.

NOTE: For a list of DTC’s, refer to the charts in this section.

OBTAINING DIAGNOSTIC TROUBLE CODES

USING DRB SCAN TOOL

WARNING: APPLY PARKING BRAKE AND/OR BLOCK WHEELS BEFORE PERFORMING ANY TEST ON AN OPERATING ENGINE.

(1) Connect DRB scan tool to the data link (diagnostic) connector located in the passengers compartment, below the center of instrument cluster on the drivers side (Fig. 1).

(2) Turn the ignition switch on, access Read Fault Screen. Record all the DTC’s shown on the DRB scan tool. Observe the malfunction indicator (check engine) lamp on the instrument panel. The lamp should light for 2 seconds then go out (bulb check).

(3) To erase DTC’s, use the Erase Trouble Code data screen on the DRB scan tool.

USING THE MALFUNCTION INDICATOR LAMP (MIL)

(1) Cycle the ignition key On - Off - On - Off - On within 5 seconds.

(2) Count the number of times the MIL (check engine lamp) on the instrument panel flashes on and off. The number of flashes represents the trouble code. There is a slight pause between the flashes representing the first and second digits of the code. Longer pauses separate individual two digit trouble codes.

An example of a flashed DTC is as follows: (3) Lamp flashes 5 times, pauses, and flashes 5 more times. This indicates a DTC code number 55.

DIAGNOSTIC TROUBLE CODE DESCRIPTIONS

GENERIC

MIL CODE*

SCAN

TOOL CODE

11 P1391** 9D Intermittent Loss of CMP or CKP

28 No Crank Reference Signal at PCM

12* Battery Disconnect Direct battery input to PCM was disconnected within the last 50 Key-on cycles.

13** P1297 27 No Change in MAP From Start to Run

14** P0107 24 MAP Sensor Voltage Too Low MAP sensor input below minimum acceptable voltage. or P0108 25 MAP Sensor Voltage Too High MAP sensor input above maximum acceptable voltage. or P1296 87 No 5 Volts To MAP Sensor 5 Volt output to MAP sensor open

15** P0500 23 No Vehicle Speed Sensor Signal

17** P0125 80 Closed Loop Temp Not Reached

Engine does not reach 50°F within 5 minutes with a vehicle speed signal. or 17 21 Engine Is Cold Too Long Engine did not reach operating temperature within acceptable limits.

(4) Lamp flashes 1 time, pauses, and then flashes 5 more times. This indicates a DTC code number 15. (5) To erase DTC’s, use the Erase Trouble Code data screen on the DRB scan tool.

USING THE VEHICLE ODOMETER

(1) Cycle the ignition key On - Off - On - Off - On within 5 seconds.

(2) Read the actual DTC number displayed on the vehicle odometer. Each number will be displayed with a slight delay between numbers.

(3) To erase DTC’s, use the Erase Trouble Code data screen on the DRB scan tool.

HEX CODE DRB SCAN TOOL DISPLAY DESCRIPTION OF DIAGNOSTIC

TROUBLE CODE

Intermittent loss of either camshaft or crankshaft position sensor or

No crank reference signal detected during engine cranking. or P1398** BA Misfire Adaptive Numerator at Limit

CKP sensor target windows have too much variation

No difference recognized between the engine MAP reading and the barometric (atmospheric) pressure reading from start-up.

No vehicle speed sensor signal detected during road load conditions. or P0720 A6 Low Output Spd Sensr RPM, Above 15 MPH

Output Speed Sensor Circuit

GENERIC

SCAN

MIL CODE*

TOOL CODE

21** P0131 9B Upstream O2s Voltage Shorted to Ground or P0132 3E Left O2 Sensor Shorted to Voltage or P0138 7E Downstream O2 Sensor Shorted to Voltage

22** P0117 1E ECT Sensor Voltage Too Low Engine coolant temperature sensor input below minimum acceptable voltage. or P0118 1F ECT Sensor Voltage Too High Engine coolant temperature sensor input above maximum acceptable voltage.

23** P0112 39 Intake Air Temp Sensor Voltage Low

24** P0121 84 TPS Voltage Does Not Agree With MAP

25** P0505 19 Idle Air Control Motor Circuits A shorted or open condition detected in one or more of the idle air control motor circuits. or P1294 8A Target Idle Not Reached Actual idle speed does not equal target idle speed.

27** P0201 15 Injector #1 Control Circuit Injector #1 output driver does not respond properly to the control signal. or

HEX CODE DRB SCAN TOOL DISPLAY DESCRIPTION OF DIAGNOSTIC

TROUBLE CODE

Tested after key off and at start to run.

Left oxygen sensor input voltage maintained above the normal operating range. or P0133 66 Upstream O2 Sensor Slow Response

Upstream oxygen sensor response slower than minimum required switching frequency or value does not go above .65 volts. or P0135 67 Upstream O2 Sensor Heater Failure

Upstream oxygen sensor heating element circuit malfunction or P0137 9C Downstream O2s Voltage Shorted to Ground

Tested after key off and at start to run.

Downstream oxygen sensor input voltage maintained above the normal operating range. or P0141 69 Downstream O2 Sensor Heater Failure

Downstream oxygen sensor heating element circuit malfunction

Intake air temperature sensor input below the maximum acceptable voltage. or P0113 3A Intake Air Temp Sensor Voltage High

Intake air temperature sensor input above the minimum acceptable voltage.

TPS signal does not correlate to MAP sensor or P0122 1A Throttle Position Sensor Voltage Low

Throttle position sensor input below the minimum acceptable voltage or P0123 1B Throttle Position Sensor Voltage High

Throttle position sensor input above the maximum acceptable voltage.

GENERIC

SCAN

MIL CODE*

TOOL CODE

31* P0441 71 Evap Purge Flow Monitor Failure

33* 10 A/C Clutch Relay Circuit An open or shorted condition detected in the A/C clutch relay circuit.

34* 0F Speed Control Solenoid Circuits An open or shorted condition detected in the Speed Control vacuum or vent solenoid circuits. or

57 Speed Control Switch Always Low

37** P0711 A4 Trans Temp Sensor, No Temp Rise After Start

HEX CODE DRB SCAN TOOL DISPLAY DESCRIPTION OF DIAGNOSTIC

TROUBLE CODE

P0202 14 Injector #2 Control Circuit Injector #2 output driver does not respond properly to the control signal. or P0203 13 Injector #3 Control Circuit Injector #3 output driver does not respond properly to the control signal. or P0204 3D Injector #4 Control Circuit Injector #4 output driver does not respond properly to the control signal. or P0205 45 Injector #5 Control Circuit Injector #5 output driver does not respond properly to the control signal. or P0206 46 Injector #6 Control Circuit Injector #6 output driver does not respond properly to the control signal. or P0207 4F Injector #7 Control Circuit Injector #7 output driver does not respond properly to the control signal. (5.2L only) or P0208 50 Injector #8 Control Circuit Injector #8 output driver does not respond properly to the control signal. (5.2L only)

Insufficient or excessive vapor flow detected during evaporative emission system operation. or P0442 A0 Evap Sys Small Leak Hole smaller than .040 in system. or P0443 12 EVAP Purge Solenoid Circuit An open or shorted condition detected in the duty cycle purge solenoid circuit. or P0455 A1 Evap Sys Gross Leak Hole larger than .040 in system. or P01494 B7 Leak Detection Pump Pressure Switch or P01495 B8 Leak Detection Pump Solenoid Circuit or P1486 BB Evap Hose Pinched Pinched hose in EVAP circuit.

MUX speed control switch below rated volts.

Transmission temperature sensor

GENERIC

SCAN

MIL CODE*

TOOL CODE

or P0712 4A Trans Temp Sensor Voltage too Low or P0713 4B Trans Temp Sensor Voltage too High or P0740 94 Torq Conv Clu, No RPM Drop At Lockup

41*** 0B Generator Field Not Switching Properly

42* 65 Fuel Pump Relay Control Circuit An open or shorted condition detected in the fuel pump relay control circuit. or

0A Auto Shutdown Relay Control Circuit

2C No ASD Relay Output Voltage at PCM

95 Fuel Level Sending Unit Volts Too Low

96 Fuel Level Sending Unit Volts Too High

97 Fuel Level Unit No Change Over Miles

43** P0300 6A Multiple Cylinder Misfire Misfire detected in multiple cylinders. or P0301 6B Cylinder #1 Misfire Misfire detected in cylinder #1. or P0302 6C Cylinder #2 Misfire Misfire detected in cylinder #2. or P0303 6D Cylinder #3 Misfire Misfire detected in cylinder #3. or P0304 6E Cylinder #4 Misfire Misfire detected in cylinder #4. or P0305 AE Cylinder #5 Misfire Misfire detected in cylinder #5. or

HEX CODE DRB SCAN TOOL DISPLAY DESCRIPTION OF DIAGNOSTIC

TROUBLE CODE

Transmission temperature sensor

Transmission temperature sensor

Relationship between engine speed and vehicle speed indicates no torque converter clutch engagement. or P0743 0C Torque Converter Clutch Soleniod CKT

An open or shorted condition detected in the torque converter part throttle unlock solenoid control circuit. or P1899 72 P/N switch Stuck In Park Or In Gear

Park/Neutral Switch Performance

An open or shorted condition detected in the generator field control circuit.

An open or shorted condition detected in the auto shutdown relay circuit. or

An Open condition Detected In The ASD Relay Output Circuit. or

Open circuit between BCM and fuel gauge sending unit. or

Circuit shorted to voltage between BCM and fuel gauge sending unit. or

No movement of fuel level sender detected.

GENERIC

SCAN

MIL CODE*

TOOL CODE

44** P1492 9A Battery Temp Sensor Voltage Too High

45** P0748 AB Governor Pressure Solenoid Control Circuit or P0753 32 Trans 3-4 Solenoid Circuit Overdrive Solenoid Circuit or P1756 8D Gov Press Not Equal To Target @ 15-20 PSI or P1763 A8 Governor Pressure Sensr Volts Too Hi or P0783 A5 3-4 Shift Sol, No RPM Drop @ 3-4 Shift 3-4 Shift Malfunction or P1757 8E Gov Pres Above 3 PSI In Gear With 0 MPH or P1762 A9 Gov Press Sen Offset Volts Too Lo Or Hi or

BC O/D Switch Pressed (LO) More than 5 Min

46*** 06 Charging System Voltage Too High

47*** 05 Charging System Voltage Too Low

HEX CODE DRB SCAN TOOL DISPLAY DESCRIPTION OF DIAGNOSTIC

TROUBLE CODE

P0306 AF Cylinder #6 Misfire Misfire detected in cylinder #6. or P0307 B0 Cylinder #7 Misfire Misfire detected in cylinder #7. (5.2L only) or P0308 B1 Cylinder #8 Misfire Misfire detected in cylinder #8. (5.2L only) or P0351 2B Ignition Coil #1 Primary Circuit Peak primary circuit current not achieved with maximum dwell time.

Battery temperature sensor input voltage above an acceptable range. or P1493 99 Battery Temp Sensor Voltage Too Low

Battery temperature sensor input voltage below an acceptable range.

Governor pressure solenoid circuit

Governor mid-pressure malfunction

Governor pressure sensor volts above rated volts. or P1764 A7 Governor Pressure Sensr Volts Too Lo

Governor pressure sensor volts below rated volts. or P1765 AD Trans 12 Volt Supply Relay Cntrl Circuit

Transmission relay circuit

Governor low pressure malfunction

Governor pressure sensor

Overdrive switch low

Battery voltage sense input above target charging voltage during engine operation.

Battery voltage sense input below target charging during engine operation. Also, no significant change detected in battery voltage during active test of generator output circuit.

GENERIC

SCAN

MIL CODE*

TOOL CODE

51** P0171 77 Fuel System Lean A lean air/fuel mixture has been indicated by an abnormally rich correction factor.

52** P0172 76 Fuel System Rich A rich air/fuel mixture has been indicated by an abnormally lean correction factor.

53** P0600 44 SPI Communication PCM Internal fault condition detected. or P0601 02 Internal Controller Failure PCM Internal fault condition detected.

54** P0340 01 No Cam Signal at PCM No camshaft signal detected during engine cranking.

55* Completion of fault code display on Check Engine lamp.

63** P1698 31 PCM Failure EEPROM Write Denied

72** P0420 70 Catalytic Converter Efficency Failure

77 52 S/C Power Relay Circuit Malfuntion detected with power feed to speed control servo soleniod * Check Engine Lamp (MIL) will not illuminate if this Diagnostic Trouble Code was recorded. Cycle Ignition key as described in manual and observe code flashed by Check Engine lamp.

** Check Engine Lamp (MIL) will illuminate during engine operation if this Diagnostic Trouble Code was recorded.

*** Generator Lamp illuminated

MONITORED SYSTEMS

There are new electronic circuit monitors that check fuel, emission, engine and ignition performance. These monitors use information from various sensor circuits to indicate the overall operation of the fuel, engine, ignition and emission systems and thus the emissions performance of the vehicle.

The fuel, engine, ignition and emission systems monitors do not indicate a specific component problem. They do indicate that there is an implied problem within one of the systems and that a specific problem must be diagnosed.

If any of these monitors detect a problem affecting vehicle emissions, the Malfunction Indicator (Check Engine) Lamp will be illuminated. These monitors generate Diagnostic Trouble Codes that can be displayed with the check engine lamp or a scan tool.

The following is a list of the system monitors: • Misfire Monitor • Fuel System Monitor • Oxygen Sensor Monitor • Oxygen Sensor Heater Monitor • Catalyst Monitor All these system monitors require two consecutive trips with the malfunction present to set a fault.

HEX CODE DRB SCAN TOOL DISPLAY DESCRIPTION OF DIAGNOSTIC

TROUBLE CODE

Unsuccessful attempt to write to an EEPROM location by the PCM.

Catalyst efficiency below required level.

Following is a description of each system monitor, and its DTC.

Refer to the appropriate Powertrain Diagnostics Procedures manual for diagnostic procedures.

DTC 21—OXYGEN SENSOR (O2S) MONITOR

Effective control of exhaust emissions is achieved by an oxygen feedback system. The most important element of the feedback system is the O2S. The O2S is located in the exhaust path. Once it reaches operating temperature 300° to 350°C (572° to 662°F), the sensor generates a voltage that is inversely proportional to the amount of oxygen in the exhaust. The information obtained by the sensor is used to calculate the fuel injector pulse width. This maintains a 14.7 to 1 Air Fuel (A/F) ratio. At this mixture ratio, the catalyst works best to remove hydrocarbons (HC), carbon monoxide (CO) and nitrogen oxide (NOx) from the exhaust.

The O2S is also the main sensing element for the Catalyst and Fuel Monitors.

The O2S can fail in any or all of the following manners:

• slow response rate

• reduced output voltage • dynamic shift • shorted or open circuits Response rate is the time required for the sensor to switch from lean to rich once it is exposed to a richer than optimum A/F mixture or vice versa. As the sensor starts malfunctioning, it could take longer to detect the changes in the oxygen content of the exhaust gas.

The output voltage of the O2S ranges from 0 to 1 volt. A good sensor can easily generate any output voltage in this range as it is exposed to different concentrations of oxygen. To detect a shift in the A/F mixture (lean or rich), the output voltage has to change beyond a threshold value. A malfunctioning sensor could have difficulty changing beyond the threshold value.

DTC 21—OXYGEN SENSOR HEATER MONITOR

If there is an oxygen sensor (O2S) shorted to voltage DTC, as well as a O2S heater DTC, the O2S fault MUST be repaired first. Before checking the O2S fault, verify that the heater circuit is operating correctly.

Effective control of exhaust emissions is achieved by an oxygen feedback system. The most important element of the feedback system is the O2S. The O2S is located in the exhaust path. Once it reaches operating temperature 300° to 350°C (572 ° to 662°F), the sensor generates a voltage that is inversely proportional to the amount of oxygen in the exhaust. The information obtained by the sensor is used to calculate the fuel injector pulse width. This maintains a 14.7 to 1 Air Fuel (A/F) ratio. At this mixture ratio, the catalyst works best to remove hydrocarbons (HC), carbon monoxide (CO) and nitrogen oxide (NOx) from the exhaust.

The voltage readings taken from the O2S sensor are very temperature sensitive. The readings are not accurate below 300°C. Heating of the O2S sensor is done to allow the engine controller to shift to closed loop control as soon as possible. The heating element used to heat the O2S sensor must be tested to ensure that it is heating the sensor properly.

The O2S sensor circuit is monitored for a drop in voltage. The sensor output is used to test the heater by isolating the effect of the heater element on the O2S sensor output voltage from the other effects.

DTC 31—LEAK DETECTION PUMP MONITOR

The leak detection assembly incorporates two primary functions: it must detect a leak in the evaporative system and seal the evaporative system so the leak detection test can be run.

The primary components within the assembly are: A three port solenoid that activates both of the functions listed above; a pump which contains a switch, two check valves and a spring/diaphragm, a canister vent valve (CVV) seal which contains a spring loaded vent seal valve.

Immediately after a cold start, between predetermined temperature thresholds limits, the three port solenoid is briefly energized. This initializes the pump by drawing air into the pump cavity and also closes the vent seal. During non test conditions the vent seal is held open by the pump diaphragm assembly which pushes it open at the full travel position. The vent seal will remain closed while the pump is cycling due to the reed switch triggering of the three port solenoid that prevents the diaphragm assembly from reaching full travel. After the brief initialization period, the solenoid is de-energized allowing atmospheric pressure to enter the pump cavity, thus permitting the spring to drive the diaphragm which forces air out of the pump cavity and into the vent system. When the solenoid is energized and de energized, the cycle is repeated creating flow in typical diaphragm pump fashion. The pump is controlled in 2 modes:

Pump Mode: The pump is cycled at a fixed rate to achieve a rapid pressure build in order to shorten the overall test length.

Test Mode: The solenoid is energized with a fixed duration pulse. Subsequent fixed pulses occur when the diaphragm reaches the Switch closure point.

The spring in the pump is set so that the system will achieve an equalized pressure of about 7.5” H20. The cycle rate of pump strokes is quite rapid as the system begins to pump up to this pressure. As the pressure increases, the cycle rate starts to drop off. If there is no leak in the system, the pump would eventually stop pumping at the equalized pressure. If there is a leak, it will continue to pump at a rate representative of the flow characteristic of the size of the leak. From this information we can determine if the leak is larger than the required detection limit (currently set at .040” orifice by CARB). If a leak is revealed during the leak test portion of the test, the test is terminated at the end of the test mode and no further system checks will be performed.

After passing the leak detection phase of the test, system pressure is maintained by turning on the LDP’s solenoid until the purge system is activated. Purge activation in effect creates a leak. The cycle rate is again interrogated and when it increases due to the flow through the purge system, the leak check portion of the diagnostic is complete.

The canister vent valve will unseal the system after completion of the test sequence as the pump diaphragm assembly moves to the full travel position.

Evaporative system functionality will be verified by using the stricter evap purge flow monitor. At an appropriate warm idle the LDP will be energized to seal the canister vent. The purge flow will be clocked up from some small value in an attempt to see a shift in the 02 control system. If fuel vapor, indicated by a shift in the 02 control, is present the test is passed. If not, it is assumed that the purge system is not functioning in some respect. The LDP is again turned off and the test is ended.

DTC 43—MISFIRE MONITOR

Excessive engine misfire results in increased catalyst temperature and causes an increase in HC emissions. Severe misfires could cause catalyst damage. To prevent catalytic convertor damage, the PCM monitors engine misfire.

The Powertrain Control Module (PCM) monitors for misfire during most engine operating conditions (positive torque) by looking at changes in the crankshaft speed. If a misfire occurs the speed of the crankshaft will vary more than normal.

DTC 51/52—FUEL SYSTEM MONITOR

To comply with clean air regulations, vehicles are equipped with catalytic converters. These converters reduce the emission of hydrocarbons, oxides of nitrogen and carbon monoxide. The catalyst works best when the Air Fuel (A/F) ratio is at or near the optimum of 14.7 to 1.

The PCM is programmed to maintain the optimum air/fuel ratio of 14.7 to 1. This is done by making short term corrections in the fuel injector pulse width based on the O2S sensor output. The programmed memory acts as a self calibration tool that the engine controller uses to compensate for variations in engine specifications, sensor tolerances and engine fatigue over the life span of the engine. By monitoring the actual fuel-air ratio with the O2S sensor (short term) and multiplying that with the program long-term (adaptive) memory and comparing that to the limit, it can be determined whether it will pass an emissions test. If a malfunction occurs such that the PCM cannot maintain the optimum A/F ratio, then the MIL will be illuminated.

DTC 64—CATALYST MONITOR

To comply with clean air regulations, vehicles are equipped with catalytic converters. These converters reduce the emission of hydrocarbons, oxides of nitrogen and carbon monoxide.

Normal vehicle miles or engine misfire can cause a catalyst to decay. A meltdown of the ceramic core can cause a reduction of the exhaust passage. This can increase vehicle emissions and deteriorate engine performance, driveability and fuel economy.

The catalyst monitor uses dual oxygen sensors (O2S’s) to monitor the efficiency of the converter. The dual O2S’s sensor strategy is based on the fact that as a catalyst deteriorates, its oxygen storage capacity and its efficiency are both reduced. By monitoring the oxygen storage capacity of a catalyst, its efficiency can be indirectly calculated. The upstream O2S is used to detect the amount of oxygen in the exhaust gas before the gas enters the catalytic converter. The PCM calculates the A/F mixture from the output of the O2S. A low voltage indicates high oxygen content (lean mixture). A high voltage indicates a low content of oxygen (rich mixture).

When the upstream O2S detects a lean condition, there is an abundance of oxygen in the exhaust gas. A functioning converter would store this oxygen so it can use it for the oxidation of HC and CO. As the converter absorbs the oxygen, there will be a lack of oxygen downstream of the converter. The output of the downstream O2S will indicate limited activity in this condition.

As the converter loses the ability to store oxygen, the condition can be detected from the behavior of the downstream O2S. When the efficiency drops, no chemical reaction takes place. This means the concentration of oxygen will be the same downstream as upstream. The output voltage of the downstream O2S copies the voltage of the upstream sensor. The only difference is a time lag (seen by the PCM) between the switching of the O2S’s.

To monitor the system, the number of lean-to-rich switches of upstream and downstream O2S’s is counted. The ratio of downstream switches to upstream switches is used to determine whether the catalyst is operating properly. An effective catalyst will have fewer downstream switches than it has upstream switches i.e., a ratio closer to zero. For a totally ineffective catalyst, this ratio will be one-toone, indicating that no oxidation occurs in the device.

The system must be monitored so that when catalyst efficiency deteriorates and exhaust emissions increase to over the legal limit, the MIL (check engine lamp) will be illuminated.

TRIP DEFINITION

For a component monitor to erase or turn off a MIL illumination for open/short diagnostics, the PCM must first recognize that the engine has operated for 2 minutes, 3 consecutive times, with no failures. All system monitors, component rationality and functionality monitors have their own trip counters. Once the appropriate conditions have been met, the monitor will be run. If the monitor fails its test, the MIL will be illuminated after completion of the first or second failed test (1 trip or 2 trips). If conditions can be repeated for 3 consecutive trips with no malfunctions, the MIL will be turned off.

Anytime the MIL is illuminated, a DTC is stored. It takes three good trips without the condition present to extinguish the MIL. The DTC remains in

PCM memory even though the MIL has been extinguished. Once the MIL is extinguished, the PCM must pass the diagnostic test for the most recent DTC for 40 warm-up cycles for the DTC to be erased from memory.

A warm-up cycle can best be described by the following:

• The engine must be running • A rise of 40°F in engine temperature must occur from the time when the engine was started

• Engine coolant temperature must reach at least 160°F Once the above conditions occur, the PCM is considered to have passed a warm-up cycle. Due to the conditions required to extinguish the MIL and erase the DTC, it is most important that after a repair has been made, all DTC’s be erased and the repair verified.

COMPONENT MONITORS

There are several components that will affect vehicle emissions if they malfunction. If one of these components malfunctions the Malfunction Indicator Lamp (Check Engine) will illuminate.

Some of the component monitors are checking for proper operation of the part. Electrically operated components now have input (rationality) and output (functionality) checks. Previously, a component like the Throttle Position sensor (TPS) was checked by the PCM for an open or shorted circuit. If one of these conditions occurred, a DTC was set. Now there is a check to ensure that the component is working. This is done by watching for a TPS indication of a greater or lesser throttle opening than MAP and engine rpm indicate. In the case of the TPS, if engine vacuum is high and engine rpm is 1600 or greater and the TPS indicates a large throttle opening, a DTC will be set. The same applies to low vacuum and 1600 rpm.

All open/short circuit checks or any component that has an associated limp in will set a fault after 1 trip with the malfunction present. Components without an associated limp in will take two trips to illuminate the MIL.

Refer to the Diagnostic Trouble Codes Description Charts in this section and the appropriate Powertrain Diagnostic Procedure Manual for diagnostic procedures.

NON-MONITORED CIRCUITS

The PCM does not monitor the following circuits, systems and conditions that could have malfunctions causing driveability problems. The PCM might not store diagnostic trouble codes for these conditions. However, problems with these systems may cause the PCM to store diagnostic trouble codes for other systems or components. For example, a fuel pressure problem will not register a fault directly, but could cause a rich/lean condition or misfire. This could cause the PCM to store an oxygen sensor or misfire diagnostic trouble code

FUEL PRESSURE

The fuel pressure regulator controls fuel system pressure. The PCM cannot detect a clogged fuel pump inlet filter, clogged in-line fuel filter, or a pinched fuel supply or return line. However, these could result in a rich or lean condition causing the PCM to store an oxygen sensor or fuel system diagnostic trouble code.

SECONDARY IGNITION CIRCUIT

The PCM cannot detect an inoperative ignition coil, fouled or worn spark plugs, ignition cross firing, or open spark plug cables.

CYLINDER COMPRESSION

The PCM cannot detect uneven, low, or high engine cylinder compression.

EXHAUST SYSTEM

The PCM cannot detect a plugged, restricted or leaking exhaust system, although it may set a fuel system fault.

FUEL INJECTOR MECHANICAL MALFUNCTIONS

The PCM cannot determine if a fuel injector is clogged, the needle is sticking or if the wrong injector is installed. However, these could result in a rich or lean condition causing the PCM to store a diagnostic trouble code for either misfire, an oxygen sensor, or the fuel system.

EXCESSIVE OIL CONSUMPTION

Although the PCM monitors engine exhaust oxygen content when the system is in closed loop, it cannot determine excessive oil consumption.

THROTTLE BODY AIR FLOW

The PCM cannot detect a clogged or restricted air cleaner inlet or filter element.

VACUUM ASSIST

The PCM cannot detect leaks or restrictions in the vacuum circuits of vacuum assisted engine control system devices. However, these could cause the PCM to store a MAP sensor diagnostic trouble code and cause a high idle condition.

PCM SYSTEM GROUND

The PCM cannot determine a poor system ground. However, one or more diagnostic trouble codes may be generated as a result of this condition. The module should be mounted to the body at all times, also during diagnostic.

PCM CONNECTOR ENGAGEMENT

The PCM may not be able to determine spread or damaged connector pins. However, it might store diagnostic trouble codes as a result of spread connector pins.

HIGH AND LOW LIMITS

The PCM compares input signal voltages from each input device with established high and low limits for

LOAD VALUE

the device. If the input voltage is not within limits and other criteria are met, the PCM stores a diagnostic trouble code in memory. Other diagnostic trouble code criteria might include engine RPM limits or input voltages from other sensors or switches that must be present before verifying a diagnostic trouble code condition.

ENGINE IDLE/NEUTRAL 2500 RPM/NEUTRAL

All Engines 2% to 8% of Maximum Load 9% to 17% of Maximum Load

EVAPORATIVE EMISSION CONTROLS

INDEX

DESCRIPTION AND OPERATION

CRANKCASE BREATHER/FILTER—5.2L

ENGINE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 CRANKCASE VENTILATION (CCV) SYSTEM—

4.0L ENGINE . . . . . . . . . . . . . . . . . . . . . . . . . . 16 DUTY CYCLE EVAP CANISTER PURGE

SOLENOID . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 EVAPORATION (EVAP) CANISTER . . . . . . . . . . . 13 EVAPORATION CONTROL SYSTEM . . . . . . . . . 13 FUEL TANK FILLER TUBE CAP . . . . . . . . . . . . . 14 LEAK DETECTION PUMP (LDP)—4.0L

CALIFORNIA EMISSIONS PACKAGE . . . . . . . . 15 POSITIVE CRANKCASE VENTILATION (PCV)

SYSTEM—5.2L ENGINE . . . . . . . . . . . . . . . . . 15 PRESSURE RELIEF/ROLLOVER VALVE . . . . . . . 13

DESCRIPTION AND OPERATION

EVAPORATION CONTROL SYSTEM

The evaporation control system prevents the emission of fuel tank vapors into the atmosphere. When fuel evaporates in the fuel tank, the vapors pass through vent hoses or tubes to a charcoal filled evaporative canister. The canister temporarily holds the vapors. The Powertrain Control Module (PCM) allows intake manifold vacuum to draw vapors into the combustion chambers during certain operating conditions.

All engines use a duty cycle purge system. The PCM controls vapor flow by operating the duty cycle EVAP purge solenoid. Refer to Duty Cycle EVAP Purge Solenoid in this section.

The 4.0L six-cylinder engine, when equipped with the California Emissions Package, will also use a Leak Detection Pump (LDP) as part of the evaporative system. This pump is used as part of OBD II requirements. Refer to Leak Detection Pump—4.0L Engine for additional information.

NOTE: The evaporative system uses specially manufactured hoses. If replacement becomes necessary, only use fuel resistant hose.

PRESSURE RELIEF/ROLLOVER VALVE

A combination fuel tank pressure relief and rollover valve is used (Fig. 1). The valve is located on the top of fuel tank (Fig. 2). This dual function valve will relieve fuel tank pressure and also prevent fuel flow page page

VEHICLE EMISSION CONTROL INFORMATION

(VECI) LABEL . . . . . . . . . . . . . . . . . . . . . . . . . 17 DIAGNOSIS AND TESTING

LEAK DETECTION PUMP (LDP) . . . . . . . . . . . . . 19 PCV VALVE TEST—5.2L ENGINE . . . . . . . . . . . . 18 VACUUM SCHEMATICS . . . . . . . . . . . . . . . . . . . 19 REMOVAL AND INSTALLATION

EVAP CANISTER . . . . . . . . . . . . . . . . . . . . . . . . 19 EVAPORATIVE CANISTER PURGE SOLENOID . 19 FUEL TANK FILLER TUBE CAP . . . . . . . . . . . . . 20 LEAK DETECTION PUMP (LDP) . . . . . . . . . . . . . 20 PRESSURE RELIEF/ROLLOVER VALVE . . . . . . . 20 SPECIFICATIONS

TORQUE CHART . . . . . . . . . . . . . . . . . . . . . . . . 21 through the fuel tank vent hoses in the event of an accidental vehicle rollover.

The valve incorporates a pressure relief mechanism that releases fuel tank pressure when the pressure increases above the calibrated sealing value.

EVAPORATION (EVAP) CANISTER

A maintenance free, EVAP canister is used on all vehicles. The EVAP canister is located in the engine compartment below the left front headlamp (Fig. 3)

or (Fig. 4). The EVAP canister is filled with granules of an activated carbon mixture. Fuel vapors entering the EVAP canister are absorbed by the charcoal granules.

Fuel tank pressure vents into the EVAP canister. Fuel vapors are temporarily held in the canister until they can be drawn into the intake manifold. The duty cycle EVAP canister purge solenoid allows the EVAP canister to be purged at predetermined times and at certain engine operating conditions.

Package—4.0L Only

DUTY CYCLE EVAP CANISTER PURGE SOLENOID

All 4.0L six-cylinder and 5.2L V-8 engines use a duty cycle EVAP canister purge solenoid. The solenoid regulates the rate of vapor flow from the EVAP

Emission Package canister to the intake manifold. The PCM operates the solenoid.

During the cold start warm-up period and the hot start time delay, the PCM does not energize the solenoid. When de-energized, no vapors are purged. The PCM de-energizes the solenoid during open loop operation.

The engine enters closed loop operation after it reaches a specified temperature and the time delay ends. During closed loop operation, the PCM cycles (energizes and de-energizes) the solenoid 5 or 10 times per second, depending upon operating conditions. The PCM varies the vapor flow rate by changing solenoid pulse width. Pulse width is the amount of time that the solenoid is energized. The PCM adjusts solenoid pulse width based on engine operating condition.

The solenoid attaches to a bracket located on the left/inner fender (Fig. 5).

FUEL TANK FILLER TUBE CAP

The loss of any fuel or vapor out of filler neck is prevented by the use of a pressure-vacuum fuel tank filler tube cap. Relief valves inside cap will release only under significant pressure of 6.58 to 8.44 kPa (1.95 to 2.5 psi). The vacuum release for all fuel filler tube caps is between .97 and 2.0 kPa (.14 and .29 psi). This cap must be replaced by a similar unit if replacement is necessary. This is in order for the system to remain effective.

CAUTION: Remove fuel tank filler tube cap before servicing any fuel system component. This is done to help relieve tank pressure.

LEAK DETECTION PUMP (LDP)—4.0L CALIFORNIA EMISSIONS PACKAGE

The leak detection pump is a device used to detect a leak in the evaporative system.

The pump contains a 3 port solenoid, a pump that contains a switch, a spring loaded canister vent valve seal, 2 check valves and a spring/diaphragm.

Immediately after a cold start, engine temperature between 40°F and 86°F, the 3 port solenoid is briefly energized. This initializes the pump by drawing air into the pump cavity and also closes the vent seal. During non-test test conditions, the vent seal is held open by the pump diaphragm assembly which pushes it open at the full travel position. The vent seal will remain closed while the pump is cycling. This is due to the operation of the 3 port solenoid which prevents the diaphragm assembly from reaching full travel. After the brief initialization period, the solenoid is de-energized, allowing atmospheric pressure to enter the pump cavity. This permits the spring to drive the diaphragm which forces air out of the pump cavity and into the vent system. When the solenoid is energized and de-energized, the cycle is repeated creating flow in typical diaphragm pump fashion. The pump is controlled in 2 modes:

PUMP MODE: The pump is cycled at a fixed rate to achieve a rapid pressure build in order to shorten the overall test time.

TEST MODE: The solenoid is energized with a fixed duration pulse. Subsequent fixed pulses occur when the diaphragm reaches the switch closure point.

The spring in the pump is set so that the system will achieve an equalized pressure of about 7.5 inches of water.

When the pump starts, the cycle rate is quite high. As the system becomes pressurized pump rate drops. If there is no leak the pump will quit. If there is a leak, the test is terminated at the end of the test mode.

If there is no leak, the purge monitor is run. If the cycle rate increases due to the flow through the purge system, the test is passed and the diagnostic is complete.

The canister vent valve will unseal the system after completion of the test sequence as the pump diaphragm assembly moves to the full travel position.

POSITIVE CRANKCASE VENTILATION (PCV) SYSTEM—5.2L ENGINE

The 5.2L V-8 engine is equipped with a closed crankcase ventilation system and a positive crankcase ventilation (PCV) valve. The 4.0L 6–cylinder engine is not equipped with a PCV valve. Refer to Crankcase Ventilation System—4.0L Engine for information.

This system consists of a crankcase PCV valve mounted on the cylinder head (valve) cover with a hose extending from the valve to the intake manifold.

A closed engine crankcase breather/filter, with a hose connecting it to the air cleaner housing, provides the source of air for system.

The PCV system operates by engine intake manifold vacuum (Fig. 8). Filtered air is routed into the crankcase through the air cleaner hose and crankcase breather/filter. The metered air, along with crankcase vapors, are drawn through the PCV valve and into a passage in the intake manifold. The PCV system manages crankcase pressure and meters blow by gases to the intake system, reducing engine sludge formation.

The PCV valve contains a spring loaded plunger. This plunger meters the amount of crankcase vapors routed into the combustion chamber based on intake manifold vacuum.

When the engine is not operating or during an engine pop-back, the spring forces the plunger back against the seat. This will prevent vapors from flowing through the valve.

During periods of high manifold vacuum, such as idle or cruising speeds, vacuum is sufficient to completely compress spring. It will then pull the plunger to the top of the valve (Fig. 10). In this position there is minimal vapor flow through the valve.

During periods of moderate manifold vacuum, the plunger is only pulled part way back from inlet. This results in maximum vapor flow through the valve (Fig. 11).

CRANKCASE VENTILATION (CCV) SYSTEM—4.0L ENGINE

4.0L 6–cylinder engines are equipped with a Crankcase Ventilation (CCV) system. The CCV sys-

tem performs the same function as a conventional PCV system, but does not use a vacuum controlled valve.

A molded vacuum tube connects a fitting on the intake manifold to a fixed orifice fitting of a calibrated size. This fitting meters the amount of crankcase vapors drawn out of the engine. The fixed orifice fitting is located on the top/rear of cylinder head (valve) cover (Fig. 12).

Flow

Vapor Flow

Maximum Vapor Flow

A fresh air supply hose is connected between a fitting on the air cleaner housing and the air inlet fitting at the top/front of cylinder head cover (Fig. 12).

When the engine is operating, fresh air enters the engine and mixes with crankcase vapors. Engine vacuum draws the vapor/air mixture through the fixed orifice and into the intake manifold. The vapors are then consumed during engine combustion.

CRANKCASE BREATHER/FILTER—5.2L ENGINE

The crankcase breather/filter (Fig. 13) is located on the cylinder head (valve) cover. The filter may be cleaned by washing in kerosene or similar solvent. Filter must then be thoroughly drained. More frequent service may be necessary for vehicles operated extensively on short run, stop and go or extended engine idle service, or extreme dust conditions.

VEHICLE EMISSION CONTROL INFORMATION (VECI) LABEL

All vehicles are equipped with a combined VECI label. This label is located in the engine compartment (Fig. 14) and contains the following:

• Engine family and displacement • Evaporative family • Emission control system schematic • Certification application • Engine timing specifications (if adjustable) • Idle speeds (if adjustable) • Spark plug and gap The label also contains an engine vacuum schematic. There are unique labels for vehicles built for sale in the state of California and the country of

Canada. Canadian labels are written in both the English and French languages. These labels are permanently attached and cannot be removed without defacing information and destroying label.

DIAGNOSIS AND TESTING

PCV VALVE TEST—5.2L ENGINE

(1) With engine idling, remove the PCV valve from cylinder head (valve) cover. If the valve is not plugged, a hissing noise will be heard as air passes through the valve. Also, a strong vacuum should be felt at the valve inlet (Fig. 15).

(2) Install the PCV valve. Remove the crankcase breather/filter. Hold a piece of stiff paper, such as a parts tag, loosely over the opening of crankcase breather/filter at the cylinder head (valve) cover (Fig. 16). (3) The paper should be drawn against the opening in the cylinder head (valve) cover with noticeable

Opening—Typical force. This will be after allowing approximately one minute for crankcase pressure to reduce.

(4) Turn engine off and remove PCV valve from cylinder head (valve) cover. The valve should rattle when shaken (Fig. 17).

(5) Replace the PCV valve and retest the system if it does not operate as described in the preceding tests. Do not attempt to clean the old PCV valve.

(6) If the paper is not held against the opening in cylinder head (valve) cover after new valve is installed, the PCV valve hose may be restricted and must be replaced. The passage in the intake manifold must also be checked and cleaned.

(7) To clean the intake manifold fitting, turn a 1/4 inch drill (by hand) through the fitting to dislodge any solid particles. Blow out the fitting with shop air. If necessary, use a smaller drill to avoid removing any metal from the fitting.

VACUUM SCHEMATICS

A vacuum schematic for emission related items can be found on the Vehicle Emission Control Information (VECI) Label. Refer to VECI Label in this group for label location.

LEAK DETECTION PUMP (LDP)

Refer to the appropriate Powertrain Diagnostic Procedures service manual for LDP testing procedures. REMOVAL AND INSTALLATION

EVAP CANISTER

The EVAP canister is located in the left front corner of vehicle below the left front headlamp (Fig. 18) or (Fig. 19).

Package—4.0L Only

REMOVAL

(1) Remove the grill. Refer to Group 23, Body. (2) Remove the front bumper/fascia assembly. Refer to Group 23, Body.

(3) Disconnect vacuum lines at canister. (4) Remove the canister mounting nuts. (5) Lower the canister through bottom of vehicle.

INSTALLATION

(1) Position canister to body.

Emission Package

(2) Install canister mounting nuts. Tighten nuts to 9 N·m (80 in. lbs.) torque. (3) Connect vacuum lines. Be sure vacuum lines are firmly connected and not leaking or damaged. If leaking, a Diagnostic Trouble Code (DTC) may be set with certain emission packages.

(4) Install the front bumper/fascia assembly and grill. Refer to Group 23, Body.

EVAPORATIVE CANISTER PURGE SOLENOID

REMOVAL

The duty cycle evaporative (EVAP) canister purge solenoid is located in the left/front corner of the engine compartment on all engine/emission packages (Fig. 20).

(1) Disconnect the electrical connector at the solenoid.

(2) Disconnect the vacuum lines at the solenoid. (3) Remove the two bracket mounting nuts and remove solenoid.

INSTALLATION

(1) Position the solenoid to vehicle. (2) Install and tighten the two bracket mounting nuts to 5 N·m (45 in. lbs.) torque.

(3) Connect the vacuum lines to the solenoid. Be sure the vacuum lines are firmly connected and not leaking or damaged. If leaking, a Diagnostic Trouble Code (DTC) may be set with certain emission packages.

(4) Connect the electrical connector to the solenoid.

PRESSURE RELIEF/ROLLOVER VALVE

The valve is located on the top of fuel tank (Fig. 21).

REMOVAL

(1) Disconnect negative battery cable. (2) Drain and remove the fuel tank. Refer to Fuel Tank removal and installation in Group 14, Fuel System.

(3) Disconnect vapor hose at valve. (4) The valve (Fig. 22) is seated in a grommet. Remove by prying one side upward and then roll the grommet out of tank.

INSTALLATION

(1) Start one side of grommet into opening in fuel tank. Using finger pressure only, press valve/grommet into place.

(2) Connect vapor hose to valve. (3) Install fuel tank. Refer to Fuel Tank Installation.

(4) Fill fuel tank. Install fuel tank filler cap. (5) Connect negative battery cable. (6) Start vehicle and check for leaks.

FUEL TANK FILLER TUBE CAP

If replacement of the fuel tank filler tube cap is necessary, it must be replaced with an identical cap to be sure of correct system operation.

CAUTION: Remove the fuel tank filler tube cap to relieve fuel tank pressure. The cap must be removed prior to disconnecting any fuel system component or before draining the fuel tank.

LEAK DETECTION PUMP (LDP)

The LDP is located in the left/front corner of the engine compartment below the EVAP canister purge solenoid (Fig. 23).

REMOVAL/INSTALLATION

(1) Remove air cleaner housing. Refer to Group 14, Fuel System for procedures.

(2) Carefully remove all vapor/vacuum lines at EVAP canister purge solenoid.

(3) Remove EVAP canister purge solenoid. (4) Disconnect electrical connector at LDP.

(5) Carefully remove vapor/vacuum lines at LDP. (6) Remove LDP mounting nuts/bolts. (7) Remove LDP from vehicle. (8) Reverse the removal procedures for installation. The vapor/vacuum lines must be firmly connected. Check the vapor/vacuum lines at both the LDP and EVAP canister solenoid for damage or leaks. If a leak is present, a Diagnostic Trouble Code (DTC) may be set.

SPECIFICATIONS

TORQUE CHART

Description Torque EVAP Canister Mounting Nuts . . .9 N·m (80 in. lbs.) EVAP Canister Purge Solenoid

Mounting Nuts . . . . . . . . . . . . . .5 N·m (45 in. lbs.) LDP Pump Bracket Nuts . . . . . . . .7 N·m (60 in. lbs.)