Important Preliminary Checks Before Starting
Perform the Diagnostic System Check - Engine Controls and verify that all of the following are true before using the Symptom tables
- The powertrain control module (PCM) and the malfunction indicator lamp (MIL) are operating correctly.
- There are no DTCs stored.
- The scan tool data is within a normal operating range.
- Verify the customer concern and locate the correct symptom in the table of contents. Check the items indicated under that symptom.
Several of the symptom procedures call for a careful visual/physical check. DO NOT neglect to perform the visual/physical check. The visual/physical check is an important procedure that can lead to the correction of a concern without further diagnosis. The performance of the visual/physical check can save valuable time. The visual/physical check should include the following
- Inspect all the PCM grounds for secure and clean connections that are in the proper location.
- Check all vacuum hoses for splits, kinks, and proper connections, as shown on the Vehicle Emission Control Information label. Check the vacuum hoses thoroughly for any type of leak or restriction.
- Inspect the air inlet ducts for collapsed or restricted sections.
- Check for air leaks at the throttle body mounting area and intake manifold sealing surfaces.
- Inspect the wiring harness for the correct connections and for damage.
For more symptom base diagnostics refer to the following tables
- «Hard Start»(ref-188837-S12955801982005090200000)
- «Surges/Chuggles»(ref-188837-S29956491822005090200000)
- «Lack of Power, Sluggishness, or Sponginess»(ref-188837-S07784071442005090200000)
- «Detonation/Spark Knock»(ref-188837-S37137566852005090200000)
- «Hesitation, Sag, Stumble»(ref-188837-S42268217632005090200000)
- «Cuts Out, Misses»(ref-188837-S10872131152005090200000)
- «Poor Fuel Economy»(ref-188837-S38958885702005090200000)
- «Poor Fuel Fill Quality»(ref-188837-S26585177572005090200000)
- «Rough, Unstable, or Incorrect Idle and Stalling»(ref-188837-S26150444692005090200000)
- «Dieseling, Run-On»(ref-188837-S18466959042005090200000)
- «Backfire»(ref-188837-S36612792352005090200000)
- «Restricted Exhaust»(ref-188835-S25637622432005090200000) in Engine Exhaust
- «Malfunction Indicator Lamp (MIL) Inoperative»(ref-188837-S29050499842005090200000)
- «Malfunction Indicator Lamp (MIL) Always On»(ref-188837-S02766911142005090200000)
Intermittent Conditions
| Checks | Action |
|---|---|
| DEFINITION: The problem may or may not turn ON the MIL or store a DTC. There is a customer concern, but the symptom can not currently be duplicated, or the DTC diagnostic table indicates the fault not present at this time. | |
| Preliminary Checks | Refer to Important Preliminary Checks in Symptoms - Engine Controls . The fault must be present in order to be diagnosed correctly with a DTC table. If the fault that set the DTC is intermittent, then the use of DTC tables may result in replacement of good parts. |
| Electrical Connections or Wiring | Electrical connections and wiring cause most intermittent conditions. Determine which circuit is suspected of having an intermittent condition. This may be indicated by DTCs with a fault not present. Check the suspect circuit for the following conditions: Any connectors that are poorly mated Any terminals that are not fully seated in the connector Any terminals that are not properly formed or damaged A poor male to female connection-Checking for proper terminal retention requires the use of the J-38125 Terminal Repair Kit. Any poor terminal-to-wire connections-Checking for poor terminal-to-wire connections requires removing the wire/terminal from the connector body. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems. Any wires that are broken inside the insulation A pierced or damaged insulation that allows water or moisture to enter the wiring-The conductor can corrode inside the insulation with little visible evidence. Look for swollen and stiff sections of wire in the suspect circuit. Refer to Wiring Repairs and to Connector Repairs in Wiring Systems for the proper procedures to use when making a circuit repair. |
| Road Test | The following tests should be performed with 2 people in order to ensure the safe operation of the vehicle. Drive the vehicle while monitoring the suspect circuit with a scan tool or a DMM connected to the circuit. Look for an abnormal reading or voltage when the malfunction occurs. An abnormal reading on the scan tool or an abnormal voltage on the DMM display is an indication that there may be a malfunction in the circuit that was being monitored. Certain DTCs must run before I/M system status can be determined. Any DTC that affects the status of an I/M system can be monitored indirectly on the scan tool under the I/M System Information selection. In order to determine which DTCs are associated with a particular I/M system test, refer to Inspection/Maintenance (I/M) System DTC Table . If an intermittent DTC is associated with a particular I/M system, monitoring the I/M system test can indicate whether the diagnostic for that DTC has run. When the I/M system test displays a YES status, indicating that the system diagnostic is complete, check for the applicable DTC in the Last Test Failed screen of the scan tool. If the DTC is not displayed, the diagnostic for that DTC has run and passed, indicating that no malfunction was present this time. All DTCs MUST BE CLEARED in order to view the Current Status of the I/M system tests. Do not forget that the I/M System Information tests only indicate that the test has run, not if the test passed or failed. The Last Test Failed screen must be checked for related DTCs in order to determine the outcome of the diagnostic test involved. |
| Scan Tool | The scan tool features that can be used to locate an intermittent conditions include the following: The scan tool Snapshot feature-The scan tool Snapshot feature can be triggered to capture and store engine parameters when a malfunction occurs. This stored information can be reviewed and compared to the Typical Scan Tool Data Values or to data values taken from a similarly equipped known-good vehicle. The Freeze Frame/Failure Records data feature-The Freeze Frame/Failure Records are stored when certain DTCs set. They typically include information to aid in reproducing the driving conditions that were present when a DTC is stored. In addition, the engine parameters are also stored. This stored information can be reviewed and compared to the typical Scan Tool Data List values or to data values taken from a similarly equipped known-good vehicle. The Freeze Frame/Failure Records data will be erased when DTC Information is cleared either with the scan tool or by disconnection of the control module power supply. |
| Intermittent malfunction indicator lamp (MIL) | The following conditions may cause intermittent MIL operation with no DTCs stored: A defective relay, control module driven solenoid, or a switch that causes electrical system interference-Usually the symptom will occur when the faulty component is operating. Any ignition control (IC) wires routed near the generator or near the secondary ignition system wires and components An ignition system secondary voltage that is arcing and shorting to ground Any poor ignition control circuit or ignition module grounds Any faulty diodes in the generator or charging system circuits The improper installation of add-on electrical devices-These can include the following: Alarm systems 2-way radios Lighting systems Electrical motors |
| Loss of DTC Memory | In order to check for proper DTC Memory function, perform the following procedure: Observe the Conditions For Running The DTC for the intake air temperature (IAT) sensor circuit high voltage DTC. Disconnect the IAT sensor connector. Operate the vehicle within the Conditions for Running the DTC. The MIL should illuminate upon completion of all the Conditions for Running the DTC. Two key cycles or drive trips may be required. An IAT sensor circuit high voltage DTC should be stored in the PCM and remain in memory when the ignition is turned OFF. A failure to store a DTC or failure of the DTC to remain in memory may indicate a faulty PCM. |
| Additional Checks | Check for faulty PCM grounds. Refer to Engine Controls Schematics . Check for open diodes (A/C clutch, charging system, etc.) that may cause electrical interference. The improper installation of add-on electrical devices-These can include the following: Alarm systems 2-way radios Lighting systems Electrical motors If the intermittent fault is believed to involve a particular sensor or component, observe the sensor or component display on a scan tool while moving the connectors and the wiring harnesses related to the sensor or the component. A change in the scan tool display can indicate the location of the fault. |
Intermittent Conditions
Hard Start
| Checks | Action |
|---|---|
| DEFINITION: The engine cranks OK, but does not start for a long time. The engine does eventually run, or may start but immediately dies. | |
| Preliminary Checks | Refer to Diagnostic System Check - Engine Controls . Refer to Symptoms - Engine Controls . Check that the driver is using the correct starting procedure. |
| Sensor Checks | Check the engine coolant temperature (ECT) sensor using a scan tool to compare the engine coolant temperature with the ambient air temperature on a cold engine. If the coolant temperature reading is more than 5°C (9°F) more or less than the ambient air temperature on a cold engine, check for a high resistance in the coolant sensor circuit or in the sensor. Refer to Temperature vs Resistance - Engine Coolant Temperature (ECT) Sensor . Check the crankshaft position (CKP) sensor engine reference signal with a scan tool. Observe the Engine Speed parameter while cranking the engine. The scan tool should indicate a steady 200-300 RPM while cranking. If erratic values, such as sudden spikes in the engine speed are displayed, the engine reference signal is not stable enough for the engine to start and run properly. |
| Fuel System Checks | Check the fuel pump relay for correct operation. Observe the fuel pump relay operation on a scan tool while cranking the engine. Check the fuel pressure. Refer to Fuel System Diagnosis . Check for water contamination in the fuel. Refer to Alcohol/Contaminants-in-Fuel Diagnosis . Check the fuel pump check valve. A faulty fuel pump check valve will allow the fuel in the lines to drain back into the tank after stopping the engine. This condition is especially troublesome on hot soak restarts. In order to check for this condition perform the following steps: Turn OFF the ignition. Install the fuel pressure gage. Refer to Fuel Pressure Gage Installation and Removal . Pressurize the fuel rail by turning the ignition key ON and OFF a few times. Turn the ignition key ON and observe the fuel pressure. The fuel pressure has to remain more than 275 kPa (40 psi) for at least 5 minutes. |
| Ignition System Checks | Check for the proper secondary voltage output with a J 26792 Spark Tester or equivalent. Refer to Electronic Ignition (EI) System Diagnosis . Inspect the spark plugs for correct operation and good ignition system performance. Refer to Spark Plug Inspection . Check for bare or shorted ignition system wiring. Check for loose ignition coil connections. |
| Additional Checks | An incorrect TP learned value can cause a hard start condition and needs to be reset. Before resetting the TP learned value, inspect for excess deposits in the throttle body and clean as necessary. Refer to Throttle Body Service and Scan Tool Output Controls . Check the Service Bulletins for any updates. |
Hard Start
Surges/Chuggles
| Checks | Action |
|---|---|
| DEFINITION: The engine has a power variation under a steady throttle or cruise. There is a feeling as if the vehicle speeds up and slows down with no change in the accelerator pedal. | |
| Preliminary Checks | Refer to Diagnostic System Check - Engine Controls . Refer to Symptoms - Engine Controls . Be sure the driver understands the A/C compressor operation. Use a scan tool to make sure the reading of the vehicle speed sensor (VSS) matches the reading of the instrument panel speedometer. Transmission performance can be affected by incorrect VSS readings. If accuracy of the VSS is a concern, refer to Speedometer and/or Odometer Inaccurate or Inoperative in Instrument Panel, Gages, and Console. |
| Sensor Checks | Test for correct operation of the engine coolant temperature (ECT) sensor. A fixed or inaccurate ECT sensor input can cause the engine to surge. Refer to Temperature vs Resistance - Engine Coolant Temperature (ECT) Sensor . Test for the correct operation of the manifold absolute pressure (MAP) sensor. A fixed or inaccurate MAP sensor input can cause the engine to surge. Observe the MAP sensor voltage parameter with a scan tool. Compare the MAP sensor voltage to that of another vehicle, with the ignition ON and the engine OFF. |
| Fuel System Checks | Determine if a rich or lean system can cause the condition. Drive the vehicle at the speed of the concern. Monitoring the Fuel Trim may help identify the problem. Lean-The Long Term Fuel Trim will be more than 17 percent. Refer to DTC P0171 or P0174 . Rich-The Long Term Fuel Trim will be more than -15 percent. Refer to DTC P0172 or P0175 . Test the fuel injectors. Perform the following procedures: The Fuel Injector Coil Test. Refer to Fuel Injector Coil Test . The Fuel Injector Balance Test-Refer to Fuel Injector Balance Test with Tech 2 . Test the fuel pressure while the condition exists. Refer to Fuel System Diagnosis . |
| Ignition System Checks | Test for the correct secondary voltage output with a J 26792 Spark Tester. Inspect the spark plugs for correct operation and good ignition system performance. Refer to Spark Plug Inspection . |
| Additional Checks | Inspect the powertrain control module (PCM) grounds for being clean, tight, and in the proper locations. Refer to Engine Controls Schematics . Inspect the positive crankcase ventilation (PCV) valve for correct operation and the correct part. Refer to Crankcase Ventilation System Inspection/Diagnosis in Engine Mechanical. Test the generator for the correct output voltage. Inspect the vacuum lines and hoses for leaks or incorrect routing. Refer to Emission Hose Routing Diagram . Inspect for the correct operation and the correct shifting of the automatic transmission. Inspect for correct operation and engagement of the torque converter clutch (TCC). Refer to Symptoms - Automatic Transmission in Automatic Transmission - 5AT. |
Surges and/or Chuggles Symptom
Lack of Power, Sluggishness, or Sponginess
| Checks | Action |
|---|---|
| DEFINITION: The engine delivers less than expected power. There is little or no increase in speed when partially applying the accelerator pedal. | |
| Preliminary Checks | Refer to Diagnostic System Check - Engine Controls . Refer to Symptoms - Engine Controls . Compare the customers vehicle with a similar unit in order to determine if the customer has an actual condition. Remove the air filter element and check for dirt or restrictions. Check the air inlet duct for any blockage or restrictions. Check the transmission shift pattern and down-shift operation. |
| Sensor/System | Inspect the throttle actuator control (TAC) system for correct operation. Refer to Throttle Actuator Control (TAC) System Description . |
| Fuel System Checks | Test for a restricted fuel filter or incorrect fuel pressure. Test the fuel injectors. Perform the following procedures: The Fuel Injector Coil Test-Refer to Fuel Injector Coil Test . The Fuel Injector Balance Test-Refer to Fuel Injector Balance Test with Tech 2 . Test for contaminated fuel. Refer to Alcohol/Contaminants-in-Fuel Diagnosis . |
| Ignition System Checks | Test for the proper ignition voltage output with a J 26792 Spark Tester. Inspect the spark plugs for correct operation and good ignition system performance. Refer to Spark Plug Inspection . Inspect the knock sensor (KS) and the sensor circuit shielding. A faulty knock sensor or signal interference could cause excessive retard of the ignition timing advance. Observe the spark parameter on a scan tool and compare with a known good vehicle. |
| Exhaust System Checks | Test the exhaust system for a possible restriction. Refer to Restricted Exhaust in Engine Exhaust. Inspect the exhaust system for damaged or collapsed pipes. Inspect the muffler for heat distress or a possible internal failure. |
| Engine Mechanical Check | Check for any of the following engine mechanical problems: A low compression An incorrect valve timing An incorrect or worn camshaft Refer to Symptoms - Engine Mechanical in Engine Mechanical-3.5L. |
| Additional Checks | If the loss of power is above 4,200 RPM, inspect for the correct operation of the Rocker Arm Oil Control system. Refer to DTC P2646 . Check the powertrain control module (PCM) grounds for being clean, tight, and in the correct locations. Refer to Engine Controls Schematics . Check the generator output voltage. |
Lack Of Power, Sluggishness, Or Sponginess
Detonation/Spark Knock
| Checks | Action |
|---|---|
| DEFINITION: A mild to severe ping that is usually worse under acceleration. The engine makes sharp metallic knocks that change with throttle opening. | |
| Preliminary Checks | Refer to Diagnostic System Check - Engine Controls . Refer to Symptoms - Engine Controls . Road test the vehicle in order to determine the severity of the condition. |
| Cooling System Checks | Check for any obvious overheating problems. Refer to Engine Overheating in Engine Cooling. Check for a low engine coolant level. Refer to Loss of Coolant in Engine Cooling. Check for a loose water pump belt. Check for restricted air flow to the engine compartment. Check for restricted coolant flow through the radiator. Check for a faulty or incorrect thermostat. Refer to Thermostat Diagnosis in Engine Cooling. Check for the correct coolant solution. The solution should be a 50/50 mix of anti-freeze and water. |
| Sensor Check | Check for an engine coolant temperature (ECT) sensor that has a shifted value. Refer to Temperature vs Resistance - Engine Coolant Temperature (ECT) Sensor . |
| Fuel System Checks | Check to determine if a lean system causes the condition. Drive the vehicle at the speed of the complaint. Monitoring the Fuel Trim will help identify the problem. If the system is lean, the Long Term Fuel Trim will be more than 20 percent. Check the fuel pressure. Refer to Fuel System Diagnosis . Check the fuel injectors. Perform the Fuel Injector Coil Test procedure and the Fuel Injector Balance Test procedure. Refer to Fuel Injector Coil Test and to Fuel Injector Balance Test with Tech 2 . Check for inferior quality fuel and the proper octane rating. Refer to Alcohol/Contaminants-in-Fuel Diagnosis . Fill the fuel tank with a known high quality fuel that meets the vehicles minimum octane requirements. Road test the vehicle and re-evaluate the vehicle performance. |
| Ignition System Checks | Check the spark plugs for the correct gap. Refer to Ignition System Specifications . Inspect the spark plugs for excessive deposits that can glow and pre-ignite the air/fuel mixture. Refer to Spark Plug Inspection . Check the spark plugs for the correct type and the correct heat range. Refer to Ignition System Specifications . |
| Engine Mechanical Checks | Check for carbon buildup. Remove the carbon with a top engine cleaner product. Follow the manufacturer instructions on the container. Check for excessive quantity oil entering the combustion chamber. Refer to Oil Consumption Diagnosis in Engine Mechanical. Check for incorrect basic engine parts such as the cam, the heads, the pistons, etc. |
| Additional Checks | Check for a dirty air filter or a restriction in the air induction system. Check for any Service Bulletins or updates. |
Detonation/Spark Knock
Hesitation, Sag, Stumble
| Checks | Action |
|---|---|
| DEFINITION: The vehicle has a momentary lack of response when pushing down on the accelerator. The condition can occur at any vehicle speed. The condition is usually most severe when trying to make the vehicle move, as from a stop sign. The condition may cause the engine to stall if severe enough. | |
| Preliminary Check | Refer to Diagnostic System Check - Engine Controls . Refer to Symptoms - Engine Controls . |
| Fuel System Checks | Check for a restricted fuel filter or incorrect fuel pressure. Refer to Fuel System Diagnosis . Check the fuel injectors. Perform the following procedures: The Fuel Injector Coil Test Procedure-Refer to Fuel Injector Coil Test . The Fuel Injector Balance Test Procedure-Refer to Fuel Injector Balance Test with Tech 2 . Check for water contamination of the fuel. Check the evaporative emission (EVAP) control system for a saturated EVAP canister. |
| Ignition System Checks | Inspect the spark plugs for correct operation and good ignition system performance. Refer to Spark Plug Inspection . |
| Additional Checks | Check the Service Bulletins for any updates. Check the generator output voltage. |
Hesitation, Sag, Stumble
Cuts Out, Misses
| Checks | Action |
|---|---|
| DEFINITION: A steady pulsation or jerking that follows engine speed, usually more pronounced as the engine load increases. The exhaust has a steady spitting sound at idle, low speed or on hard acceleration. | |
| Preliminary Checks | Refer to Diagnostic System Check - Engine Controls . Refer to Symptoms - Engine Controls . |
| Sensor Checks | Check the engine coolant temperature (ECT) sensor using a scan tool in order to compare the engine coolant temperature with the ambient air temperature on a cold engine. If the coolant temperature reading is more than 5°C (9°F) more or less than the ambient air temperature on a cold engine, check for a high resistance in the coolant sensor circuit or in the sensor. Refer to Temperature vs Resistance - Engine Coolant Temperature (ECT) Sensor . |
| Fuel System Checks | Check for a restricted fuel filter or an incorrect fuel pressure. Refer to Fuel System Diagnosis . Check the fuel injectors. Perform the Fuel Injector Coil Test procedure and the Fuel Injector Balance Test procedure. Refer to Fuel Injector Coil Test and Fuel Injector Balance Test with Tech 2 . Perform the engine cylinder balance test: Start the engine. Use the scan tool in order to turn OFF each fuel injector one at a time. Refer to Scan Tool Output Controls . Observe the engine speed for each cylinder while testing. If there is an equal RPM drop on all cylinders (equal to within 50 RPM), the output from each cylinder is satisfactory. Check for water contamination of the fuel. |
| Ignition System Checks | Test the ignition system for the correct operation. Verify that each coil has good crisp, blue spark. Diagnose and repair any coil with a weak spark output. Refer to Electronic Ignition (EI) System Diagnosis . |
| Engine Mechanical Checks | Check for any of the following engine mechanical problems: Any faulty hydraulic lifter assemblies Any broken or weak valve springs An incorrect valve timing An incorrect or worn camshaft Check the intake and exhaust manifold passages for casting flash. Refer to the Symptoms - Engine Mechanical in Engine Mechanical-3.5L. |
| Additional Checks | An engine miss condition can be caused by electromagnetic interference (EMI) on the reference circuit. EMI can usually be detected by monitoring the engine speed with a scan tool. A sudden increase in speed with little change in the actual engine speed change indicates EMI is present. Verify the powertrain control module (PCM) grounds are clean, tight, and in the correct locations. Refer to Engine Controls Schematics . |
Cuts Out, Misses Symptom
Poor Fuel Economy
| Checks | Action |
|---|---|
| DEFINITION: Fuel economy, as measured by an actual road test, is noticeably lower than expected. Also, the economy is noticeably lower than it was on this vehicle at one time, as previously shown by an actual road test. | |
| Preliminary Checks | Refer to Diagnostic System Check - Engine Controls . Refer to Symptoms - Engine Controls . Check the air cleaner element for dirt or restrictions. Visually and physically check the vacuum hoses for splits, kinks, and proper connections as shown on the Vehicle Emission Control Information label. Check the owners driving habits for any of the following: The A/C system defroster mode is ON all the time. The tires are improperly inflated. Heavy loads are frequently being carried. Heavy acceleration and high speeds are common. Frequent short trips Prolonged periods of idling Driving on unpaved or rough roads Suggest that the owner refill the fuel tank and recheck the fuel economy. |
| Fuel System Checks | Check the type, quality, and alcohol content of the fuel. Oxygenated fuels have lower energy and may deliver reduced fuel economy. Refer to Alcohol/Contaminants-in-Fuel Diagnosis . Check for the correct fuel pressure. Refer to Fuel System Diagnosis . |
| Ignition System Checks | Inspect the spark plugs for correct operation and good ignition system performance. Refer to Spark Plug Inspection . Check the ignition coil boots for cracking, chafing, and loose connections. Observe the Spark parameter on the scan tool at idle, while operating the rear defogger, the A/C system, or the headlights. Check the knock sensor (KS) and the sensor circuit shielding. A faulty knock sensor or signal interference could cause excessive retard of the ignition timing advance. Observe the Spark parameter on a scan tool and compare with a known good vehicle. |
| Cooling System Checks | Check for the correct engine coolant level. Check the engine thermostat for always being open or for the wrong heat range. Refer to Thermostat Diagnosis in Engine Cooling. |
| Additional Checks | Check the transmission shift pattern and the torque converter clutch (TCC) operation in vehicles equipped with an automatic transmission. Refer to Symptoms - Automatic Transmission in Automatic Transmission. Check for dragging brakes. Refer to Brakes Drag in Hydraulic Brakes. Check for uneven or premature tire wear. A suspension misalignment can cause reduced fuel economy. Refer to Measuring Wheel Alignment in Wheel Alignment. Verify that the tires and wheels are similar to OEM. Wide performance tires create more drag and taller tires can cause odometer discrepancies. Check for the speedometer for proper calibration. Refer to Speedometer and/or Odometer Inaccurate or Inoperative in Instrument Panel, Gages, and Console. Check for a green engine. Fuel economy may not be near expected levels until the engine has had 5 000-8 000 km (3,000-5,000 miles) to break in. Check for add-on equipment like luggage racks and carriers. Wind resistance can lower fuel economy. Check the Service Bulletins for any updates or information. |
Poor Fuel Economy
Poor Fuel Fill Quality
| Concern | Causes |
|---|---|
| DEFINITION: Difficulty when refueling the vehicle. | |
| Difficult to fill | The fuel filler pipe check valve is stuck closed. The fill limiter vent valve (FLVV) is stuck closed. Any restricted vapor lines or hoses The EVAP canister is restricted. A fuel with high reid vapor pressure characteristics. A high fuel temperature The fuel filler hose/pipe is pinched, kinked, or blocked. |
| Over fill | The pressure relief valve in the fill limiter vent valve (FLVV) is stuck open. The pressure relief valve in the FLVV is leaking. The FLVV is stuck open. The FLVV is leaking. |
| Pre-mature shut-off of the fuel dispensing nozzle | The fill limiter vent valve (FLVV) is stuck closed. Any restricted vapor lines or hoses The EVAP canister is restricted. A fuel with high reid vapor pressure characteristics A high fuel temperature |
| Fuel spitback | The fuel filler pipe check valve is stuck open. The filler pipe check valve is stuck closed. The filler pipe check valve is leaking. A fuel with high reid vapor pressure characteristics. A high fuel temperature |
| Liquid fuel in the EVAP canister | The fill limiter vent valve is stuck open. The fill limiter vent valve is leaking. |
| Liquid fuel leak | The pressure relief valve in the fill limiter vent valve (FLVV) is stuck open. The pressure relief valve in the FLVV is leaking. The fuel filler hose is loose or torn. The FLVV is stuck open. |
| Fuel odor | The pressure relief valve in the fuel limiter vent valve (FLVV) is stuck open. The pressure relief valve in the FLVV is leaking. The EVAP canister is saturated with fuel. |
Poor Fuel Fill Quality
Rough, Unstable, or Incorrect Idle and Stalling
| Checks | Action |
|---|---|
| DEFINITION: The engine runs unevenly at idle. If severe enough, the engine or vehicle may shake. The engine idle speed may vary in RPM. Either condition may be severe enough to stall the engine. The engine idles at an incorrect speed. | |
| Preliminary Check | Refer to Diagnostic System Check - Engine Controls . Refer to Symptoms - Engine Controls . |
| Sensor Checks | Inspect the engine coolant temperature (ECT) sensor. A fixed or inaccurate ECT sensor reading can cause the engine idle to surge or race. Using the scan tool, compare the ECT with the ambient air temperature on a cold engine. If the engine coolant is 5°C (9°F) more than or 5°C (9°F) less than the ambient air temperature, inspect the resistance of the coolant sensor. Refer to Temperature vs Resistance - Engine Coolant Temperature (ECT) Sensor . If the ECT is significantly less than the ambient air temperature, inspect the coolant sensor electrical circuit for high resistance. Inspect the throttle actuator control (TAC) system for correct operation. |
| Fuel System Checks | Inspect the operation of the fuel system for rich or lean condition. Operate the vehicle under the conditions that caused the concern. Monitor the Fuel Trim parameter on a scan tool in order to identify the problem. Lean-The Long Term Fuel Trim will be more than 17 percent. Refer to Diagnostic Aids in DTC P0171 or P0174 . Rich-The Long Term Fuel Trim will be more than -15 percent. Refer to Diagnostic Aids in DTC P0172 or P0175 Test the fuel pressure while the condition exists. Refer to Fuel System Diagnosis . Inspect the evaporative emission (EVAP) control system for a saturated EVAP canister. Test the fuel injectors for leaking. Refer to Fuel Injector Balance Test with Tech 2 . |
| Ignition System Checks | Test for the proper secondary voltage output with a J 26792 Spark Tester. Inspect the spark plugs for correct operation and good ignition system performance. Refer to Spark Plug Inspection . Inspect the ignition coil boots for damage. |
| Engine Mechanical Check | Inspect for the following engine mechanical conditions: Any faulty hydraulic lifter assemblies Any broken or weak valve springs A low compression An incorrect valve timing Any sticking or leaking valves An incorrect or worn camshaft Refer to the Symptoms - Engine Mechanical in Engine Mechanical - 3.5L. |
| Additional Checks | Inspect for vacuum leaks. Vacuum leaks can cause a higher than normal idle speed. Verify the PCM grounds are clean, tight, and in the proper locations. Refer to Engine Controls Schematics . An incorrect TP learned value can cause a rough or incorrect idle speed concern and needs to be reset. Before resetting the TP learned value, inspect for excess deposits in the throttle body and clean as necessary. Refer to Throttle Body Service and Scan Tool Output Controls . Check the scan tool to determine if the PCM is receiving an A/C signal. The idle speed should be increased with the A/C ON. Inspect the battery cables and the ground straps. They should be clean and secure. Inspect the A/C refrigerant pressure for being too high or for a faulty high pressure switch. Refer to Air Conditioning (A/C) System Performance Test (L61) Air Conditioning (A/C) System Performance Test (L66) in Heating, Ventilation, and Air Conditioning. The engine will run rough and the engine can stall if the rocker arm oil control solenoid. stuck ON. Refer to DTC P2647 . Inspect the positive crankcase ventilation (PCV) valve for correct operation and the correct part. Refer to Crankcase Ventilation System Inspection/Diagnosis in Engine Mechanical - 3.5L. Inspect for the correct operation of the exhaust gas recirculation (EGR) valve. An EGR valve that leaks can cause a rough idle condition. Verify that the PCM is increasing the idle speed when the P/S system pressure is increased on turns. Inspect for broken or worn motor and transmission mounts. |
Rough, Unstable, or Incorrect Idle, Stalling
Dieseling, Run-On
| Checks | Action |
|---|---|
| DEFINITION: Engine continues to run when turning the ignition OFF, but runs very roughly. If the engine runs smoothly, check the ignition switch and adjustment. | |
| Preliminary Check | Refer to Diagnostic System Check - Engine Controls . Refer to Symptoms - Engine Controls . |
| Fuel System Checks | Check the evaporative emission (EVAP) control system for proper operation or a saturated EVAP canister. Check the fuel injectors for leaking. Refer to Fuel Injector Balance Test with Tech 2 . |
Dieseling, Run-On
Backfire
| Checks | Action |
|---|---|
| DEFINITION: The fuel ignites in the intake manifold, or in the exhaust system, making a loud popping noise. | |
| Preliminary Check | Refer to Diagnostic System Check - Engine Controls . Refer to Symptoms - Engine Controls . |
| Ignition System Checks | Check for the proper ignition coil output voltage with a J 26792 Spark Tester or equivalent. Inspect the spark plugs for correct operation and good ignition system performance. Refer to Spark Plug Inspection . Inspect the ignition coil boots for damage. |
| Engine Mechanical Checks | Check for any of the following engine mechanical problems: Any broken or weak valve springs A low compression Any sticking or leaking valves An incorrect valve timing An incorrect or worn camshaft Refer to Symptoms - Engine Mechanical in Engine Mechanical-3.5L. Check the intake and the exhaust system for casting flash or other restrictions. |
Backfire
Conditions for Updating the I/M System Status
Each system requires at least one, and sometimes several, diagnostic tests. The results of these tests are reported by a diagnostic trouble code (DTC). A system monitor is complete when either all of the DTCs comprising the monitor have Run and Passed, or any one of the DTCs comprising the monitor have illuminated the malfunction indicator lamp (MIL). Once all of the tests are completed, the I/M System Status display will indicate YES in the Completed column. For example, when the HO2S Heater Test indicates YES, all of the oxygen sensor heaters have been diagnosed. If the vehicle has four heated oxygen sensors, all four heater circuits have been diagnosed. The I/M System Status will indicate NO under the Completed column when any of the required tests for that system have not run. The following is a list of conditions that would set the I/M System Status indicator to NO
- The vehicle is new from the factory and has not yet been driven through the necessary drive conditions to complete the tests.
- The battery has been disconnected or discharged below operating voltage.
- The control module power or ground has been interrupted.
- The control module has been reprogrammed.
- The control module DTCs have been cleared as part of a service procedure.
Monitored Emission Control Systems
The OBD II system monitors all emission control systems that are on-board. Not all vehicles have a full complement of emission control systems. For example, a vehicle may not be equipped with secondary air injection (AIR) or exhaust gas recirculation (EGR). The OBD II regulations require monitoring of the following
- Air conditioning system
- Catalytic converter efficiency
- Comprehensive component monitoring - Emission related inputs and outputs
- Evaporative emissions (EVAP) system
- Exhaust gas recirculation (EGR) system
- Fuel delivery system
- Heated catalyst monitoring
- Misfire monitoring
- Oxygen sensor system (O2S or HO2S)
- Oxygen sensor heater system (HO2S heater)
- Secondary air injection (AIR) system
For the specific DTCs required for each system, refer to Inspection/Maintenance (I/M) System DTC Table . Systems such as fuel delivery, misfire, and comprehensive components may not be listed in a system status list. These tests run continuously on some vehicles and may not require an indicator.