Important Preliminary Checks Before Starting
Before using the Symptom tables use the following
- Perform «Diagnostic System Check - Vehicle»(ref-200355-S37572612702005102000000) in Vehicle DTC Information and verify all of the following items: Ensure no DTCs are stored. Check that the scan tool data is within normal operating range. Refer to «Scan Tool Data List»(ref-200441-S32565338242005102000000) .
- Verify the customer complaint.
- Perform the Visual/Physical Check in this section.
Locate the correct symptom in the list at the end of this section. Follow the procedures in the appropriate diagnostic table. If the condition cannot be duplicated or is determined to be intermittent, refer to Intermittent Conditions .
Visual/Physical Check
Several of the symptom procedures call for a careful visual and physical inspection. This can lead to correcting a condition without further tests and can save valuable time. This inspection should include the following areas
- Inspect the PCM grounds for being clean, tight, and in their proper location. Refer to «Power and Grounding Component Views»(ref-200394-S07235233162005102000000) in Wiring Systems.
- Inspect vacuum hoses for splits, kinks, and proper connections, as shown on Vehicle Emission Control Information label. Inspect thoroughly for any type of leak or restriction.
- Inspect the air intake ducts for being collapsed, damaged areas, looseness, improper installation, or leaking, especially between the mass air flow (MAF) sensor and the throttle body.
- Inspect for air leaks at throttle body mounting area, mass air flow (MAF) sensor and intake manifold sealing surfaces.
- Inspect the wiring harness for poor connections, pinches, cuts, or other damage.
- Inspect for loose, damaged, or missing sensors and/or components.
Use the following tables when diagnosing a symptom complaint
- «Intermittent Conditions»(ref-200402-S18543456152005102000000)
- «Hard Start»(ref-200402-S26250410032005102000000)
- «Surges/Chuggles»(ref-200402-S34863956832005102000000)
- «Lack of Power, Sluggishness, or Sponginess»(ref-200402-S42714761152005102000000)
- «Detonation/Spark Knock»(ref-200402-S23245713612005102000000)
- «Hesitation, Sag, Stumble»(ref-200402-S07639209182005102000000)
- «Cuts Out, Misses»(ref-200402-S29910283662005102000000)
- «Poor Fuel Economy»(ref-200402-S14510107502005102000000)
- «Poor Fuel Fill Quality»(ref-200402-S30080474692005102000000)
- «Rough, Unstable, or Incorrect Idle and Stalling»(ref-200402-S06969849672005102000000)
- «Dieseling, Run-On»(ref-200402-S00990386722005102000000)
- «Backfire»(ref-200402-S18076082172005102000000)
- «Malfunction Indicator Lamp (MIL) Inoperative»(ref-200402-S26808560732005102000000)
- «Malfunction Indicator Lamp (MIL) Always On»(ref-200402-S19407298532005102000000)
- «Engine Cranks but Does Not Run»(ref-200402-S14109756132005102000000)
Intermittent Conditions
| Inspection or Test | Action |
|---|---|
| DEFINITION: Whether the symptom is a DTC or a customer complaint, the condition cannot be duplicated. | |
| Preliminary | Perform the Diagnostic System Check-Engine Controls before starting. Refer to Diagnostic System Check - Vehicle in Vehicle DTC Information. |
| Harness or Connector | Many intermittent open or shorted circuits come and go with harness or connector movement caused by the following type conditions: Vibration Engine torque Bumps or rough pavement Test for intermittents by performing the applicable procedure from the following list: Move related connectors and wiring while monitoring the appropriate scan tool data. Move related connectors and wiring with the component commanded ON and OFF, with the scan tool. Observe the component operation. With the engine running, move related connectors and wiring while monitoring engine operation. Verify whether the harness or connector movement affects any of the following systems: Data displayed Component or system operation Engine operation Repair the components as necessary. Refer to Electrical Connections or Wiring in this table. |
| Electrical Connections or Wiring | Intermittents are usually caused by one or more of the following conditions: Poor electrical connections Terminal tension Wiring problems Carefully inspect the suspected circuit for the following conditions: Poor mating of the connector halves Terminals backed out or not fully seated in the connector body Improperly formed or damaged terminals-Test for poor terminal tension. Poor terminal to wire connections including terminals crimped over insulation-This requires removing the terminal from the connector body. Corrosion or water intrusion- Pierced or damaged insulation can allow 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 circuits. Wires that are broken inside the insulation Pinched, cut, or rubbed through wiring in the harness Wiring that is in contact with hot exhaust components Repair the condition as necessary. Refer to Testing for Intermittent Conditions and Poor Connections and Wiring Repairs in Wiring Systems. |
| Control Module Power and Grounds Component Power and Grounds | Poor power or ground connections can cause widely varying symptoms. Test all control module power circuits. Many vehicles have multiple circuits supplying power to the control module. Other components in the system may have separate power circuits that may also need to be tested. Inspect connections at the module or component connectors, fuses, and any intermediate connections between the power source and the module or component. A test lamp or a DMM may indicate that voltage is present, but neither tests the ability of a circuit to carry sufficient current. Ensure that the circuit can carry the current necessary to operate the component. Refer to Power Distribution Schematics in Wiring Systems. Test all control module ground and system ground circuits. The control module may have multiple ground circuits. Other components in the system may have separate grounds that may also need to be tested. Inspect grounds for clean and tight connections at the grounding point. Inspect the connections at the component and in splice packs, where applicable. Ensure that the circuit can carry the current necessary to operate the component. Refer to Ground Distribution Schematics in Wiring Systems. |
| Temperature Sensitivity | An intermittent condition may occur when a component or connection reaches normal operating temperature. The condition may occur only when the component or connection is cold, or only when the connection is hot. The following data may help to diagnose this type of intermittent condition: Freeze Frame/Failure Records Scan tool snapshot Vehicle data recorder If the intermittent is related to heat, review the following data: High ambient temperatures Underhood or engine generated heat Circuit generated heat due to a poor connection or high electrical load Higher than normal load conditions, such as towing If the intermittent is related to cold, review the following data: Low ambient temperatures-In extremely low temperatures, ice may form in a connection or component. Test for water intrusion. The condition only occurs on a cold start. The condition is not present after the vehicle warms up. Information from the customer may help to determine if the trouble follows a pattern that is temperature related. |
| Electromagnetic Interference (EMI) and Electrical Noise | Some electrical components or circuits are sensitive to electromagnetic interference (EMI) or other types of electrical noise. Perform the following procedures: Inspect for a misrouted harness that is too close to a high voltage or high current device. This condition may induce electrical noise on a circuit that could interfere with normal circuit operation. Inspect for wires that are too close to the following devices: Secondary ignition components Motors The generator Determine whether the electrical system interference is caused by a malfunctioning relay, powertrain control module (PCM) driven solenoid or switch. These components may cause a sharp electrical surge. Normally, the condition will occur when the malfunctioning component is operating. Determine whether non-factory or aftermarket add-on accessories are installed in the vehicle. These accessories may lead to an emission related OBD II failure. Determine if any of the following non-factory or aftermarket add-on accessories is causing the intermittent: Lights 2-way radios Amplifiers Electric motors Remote starters Alarm systems Cell phones Test for an open diode across the A/C compressor clutch and for other open diodes. Some relays may contain a clamping diode. Test for proper performance of the generator. Refer to Diagnostic System Check - Vehicle in Vehicle DTC Information. If a DTC is determined to be intermittent, and the tests in this section do not reveal a condition, refer to Vehicle Data Recorder later in this table. Refer to Checking Aftermarket Accessories in Wiring Systems. |
| Incorrect PCM Programming | There are only a few situations when reprogramming a PCM is appropriate, such as the following: A new service PCM is installed. A PCM from another vehicle is installed. Revised software or calibration files have been released for this vehicle. IMPORTANT: DO NOT re-program the PCM with the same software or calibration files that are already present in the PCM. This is not an effective repair for any type of driveability problem. Verify that the PCM contains the correct software or calibration. If incorrect programming is found, reprogram the PCM with the most current software or calibration. Refer to Service Programming System (SPS) in Programming and Setup. |
| Duplicating Failure Conditions | If none of the previous tests are successful, attempt to duplicate or capture the failure conditions. Freeze Frame/Failure Records, where applicable, contains the conditions that were present when the DTC set. Perform the following procedure: Review and record Freeze Frame/Failure Records. Clear the DTCs using the scan tool. Turn the key to OFF and wait 15 seconds. Operate the vehicle under the same conditions that were noted in Freeze Frame/Failure Records, as closely as possible. The vehicle must also be operating within the Conditions for Running the DTC. Refer to Conditions for Running the DTC in the supporting text of the DTC being diagnosed. Monitor DTC Status for the DTC being tested. The scan tool will indicate Ran, when the enabling conditions have been satisfied long enough for the DTC to run. The scan tool will also indicate whether the DTC passed or failed. An alternate method is to drive the vehicle with the DMM connected to a suspected circuit. An abnormal reading on the DMM when the condition occurs, may help you locate the condition. |
| Scan Tool Snapshot | The scan tool can be set up to take a snapshot of the parameters available via serial data. The snapshot function records live data over a period of time. The recorded data can be played back and analyzed. The scan tool can also graph parameters singly or in combinations of parameters for comparison. The snapshot can be triggered manually at the time the symptom is noticed, or set up in advance to trigger when a DTC sets. An abnormal value captured in the recorded data may point to a system or component that needs to be investigated further. Refer to the scan tool user instructions for more information on the Snapshot function. |
| Vehicle Data Recorder | The J 42598 Vehicle Data Recorder is connected to the data link connector (DLC) and sent with the customer. See Special Tools . The J 42598 captures data for later retrieval and analysis by the technician. See Special Tools . Refer to the vehicle data recorder user instructions for more information. |
| IMPORTANT |
|---|
| DO NOT re-program the PCM with the same software or calibration files that are already present in the PCM. This is not an effective repair for any type of driveability problem. |
Intermittent Conditions
Hard Start
| Inspections | Action |
|---|---|
| DEFINITION: The engine cranks normally, but does not start in a normal amount of time. The engine does eventually run, or may start but immediately dies. | |
| Preliminary | Refer to Important Preliminary Check Before Starting in Symptoms - Engine Controls . Search for bulletins. Make sure the vehicle operator is using the correct starting procedure. |
| Sensor/System | Monitor the engine coolant temperature (ECT) sensor with the scan tool. Compare the engine coolant temperature with the ambient air temperature on a cold engine. If the coolant temperature reading is more than 5 degrees more or less than the ambient air temperature on a cold engine, check for high resistance in the coolant sensor circuit. |
| Fuel System | Inspect for a restricted exhaust. Refer to Restricted Exhaust in Engine Exhaust. Inspect the fuel pump relay for proper operation. The fuel pump should operate for the first 2 seconds when turning ON the ignition. Refer to Fuel Pump Electrical Circuit Diagnosis . Test the fuel pressure. Refer to Fuel System Diagnosis . Inspect for water contamination in the fuel. Refer to Alcohol/Contaminants-in-Fuel Diagnosis (with Special Tool) or Alcohol/Contaminants-in-Fuel Diagnosis (without Special Tool) . Perform the fuel injector coil test. Refer to Fuel Injector Coil Test . Perform the fuel injector balance test. Refer to Fuel Injector Balance Test with Tech 2 . Inspect the fuel pump check valve. Refer to Fuel System Diagnosis . |
| Ignition System | Inspect the spark plugs for the following conditions: Wet plugs Cracks Wear Improper gap Burned electrodes Heavy deposits Refer to Spark Plug Inspection . Inspect for loose ignition coil connections. Inspect for loose ignition control module connections. Inspect for a faulty control module or ignition system grounds. |
| Engine Mechanical | Inspect for the following conditions: Improper valve timing Low compression-Refer to Engine Compression Test in Engine Mechanical. Worn rocker arms-Refer to Valve Rocker Arm and Valve Lash Adjuster Cleaning and Inspection in Engine Mechanical. Broken or weak valve springs Worn camshaft lobes-Refer to Camshafts Cleaning and Inspection in Engine Mechanical. Proper Cam Phaser operation-Refer to Exhaust Camshaft Position Actuator Description in Engine Mechanical. |
| Additional | Inspect for a restricted exhaust. Refer to Restricted Exhaust in Engine Exhaust. |
Hard Start
Surges/Chuggles
| Inspections | Action |
|---|---|
| DEFINITION: The engine has a power variation under a steady throttle or cruise. The vehicle feels as if it speeds up and slows down with no change in the accelerator pedal position. | |
| Preliminary Inspections | Refer to Symptoms - Engine Controls . Be sure that the driver understands the torque converter clutch operation. Be sure that the driver understands the A/C compressor operation. Ensure that the transmission fluid is at the proper level. |
| Sensor/System | Display the scan tool parameters for the various engine controls sensors. Inspect for any abnormal readings. |
| Fuel System | Inspect for a rich or lean symptom that causes the condition. Drive the vehicle at the speed of the complaint. Monitoring the fuel trim will help identify the condition. Lean-The long term fuel trim will be more than 150. Rich-The long term fuel trim will be less than 115. Test the fuel pressure while the condition exists. Refer to Fuel System Diagnosis . Inspect the in-line fuel filter for a restrictions. |
| Ignition System | Inspect the spark plugs. Remove the plugs and inspect for the following conditions: Wetness Cracks Wear Improper gap Burned electrodes Heavy deposits Refer to Spark Plug Inspection . |
| Additional | Inspect the control module grounds for being clean, tight, and in their proper locations. Refer to Power and Grounding Component Views in Wiring Systems. Test the generator output voltage. Refer to Diagnostic System Check - Vehicle in Vehicle DTC Information. Inspect the vacuum hoses for kinks or leaks. Inspect the torque converter clutch (TCC) operation. Refer to Torque Converter Diagnosis Procedure in Automatic Transmission. Inspect the exhaust system for a possible restriction. Refer to Restricted Exhaust in Engine Exhaust. |
Surges/Chuggles
Lack of Power, Sluggishness, or Sponginess
| Inspections | Action |
|---|---|
| DEFINITION: The engine delivers less than expected power. There is little or no increase in speed when partially applying the accelerator pedal. | |
| Preliminary | Refer to Symptoms - Engine Controls . Compare the customer vehicle with a similar unit. Verify the customer concern. Remove the air filter and check for dirt or a restriction. Inspect the transmission shift pattern and the downshift operation. Refer to Symptoms - Automatic Transmission in Automatic Transmission. |
| Fuel System | Inspect for a restricted fuel filter, contaminated fuel, or improper fuel pressure. Refer to Fuel System Diagnosis . Perform the fuel injector balance test. Refer to Fuel Injector Balance Test with Tech 2 and Fuel Injector Balance Test with Special Tool . |
| Exhaust System | Inspect 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. |
| Additional | Inspect the control module grounds for being clean, tight, and in their proper location. Refer to Power and Grounding Component Views in Wiring Systems. Inspect the torque converter clutch (TCC) operation. Refer to Torque Converter Diagnosis Procedure in Automatic Transmission. Inspect the A/C operation. Refer to HVAC Compressor Clutch Does Not Engage or HVAC Compressor Clutch Does Not Disengage in HVAC Systems- Manual. Monitor the knock sensor (KS) system for retarded timing. |
| Engine Mechanical | Inspect the engine for the proper operation of the following items: Engine compression-Refer to Engine Compression Test in Engine Mechanical. Valve timing Improper or worn camshaft-Refer to Camshafts Cleaning and Inspection in Engine Mechanical. |
Lack of Power, Sluggishness, or Sponginess
Detonation/Spark Knock
| Inspections | Action |
|---|---|
| DEFINITION: A mild to severe ping, usually worse under acceleration. The engine makes sharp metallic knocks that change with the throttle opening. | |
| Preliminary | Refer to Symptoms - Engine Controls . Verify the customer's concern. |
| Cooling System | Inspect for a low engine coolant level. Inspect for a correct coolant mixture. Inspect for the proper tension on the drive belts. Refer to Drive Belt Tensioner Diagnosis in Engine Mechanical. Inspect for restricted air flow through the radiator, or restricted coolant flow. Inspect for a faulty thermostat. Refer to Thermostat Diagnosis in Engine Cooling. |
| Sensor/System | Inspect for an engine coolant temperature (ECT) sensor that has a shift in value. Refer to Temperature vs Resistance . |
| Fuel System | 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 150. Test the fuel pressure. Refer to Fuel System Diagnosis . Inspect for a poor fuel quality and a proper octane rating. If the fuel trim readings are normal and there are no engine mechanical concerns, then fill the fuel tank with a known good fuel and re-evaluate the vehicle performance. |
| Ignition System | Inspect the spark plugs for their proper heat range and gap. Inspect the knock sensor (KS) system operation. Inspect the ignition timing. |
| Engine Mechanical | Inspect for carbon build up. Remove the carbon with a top engine cleaner. Follow the instructions on the can. Test the combustion chamber pressure by performing a compression test. Refer to Engine Compression Test in Engine Mechanical. |
| Additional | Inspect the torque converter clutch (TCC) operation. Refer to Torque Converter Diagnosis Procedure in Automatic Transmission. Search for Service Bulletins for calibration updates. |
Detonation/Spark Knock
Hesitation, Sag, Stumble
| Inspections | Action |
|---|---|
| DEFINITION: The vehicle has a momentary lack of response when depressing 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 the condition is severe enough. | |
| Preliminary | Refer to Symptoms - Engine Controls . |
| Fuel System | Test the fuel pressure. Refer to Fuel System Diagnosis . Inspect the throttle position (TP) sensor for binding or sticking. Voltage should increase at a steady rate as the throttle moves toward wide open throttle (WOT). Test for water contamination in the fuel. Refer to Alcohol/Contaminants-in-Fuel Diagnosis (with Special Tool) or Alcohol/Contaminants-in-Fuel Diagnosis (without Special Tool) . Test the canister purge system for proper operation. Perform the fuel injector coil test. Refer to Fuel Injector Coil Test . Test for low fuel pressure after a cold start or during a moderate or full throttle acceleration. |
| Ignition System | Inspect for fouled spark plugs. Inspect for proper ignition system performance. |
| Additional | Search for Service Bulletins for calibration updates. Inspect for a restricted exhaust. Refer to Restricted Exhaust in Engine Exhaust. |
Hesitation, Sag, Stumble
Cuts Out, Misses
| Inspections | Action |
|---|---|
| DEFINITION: A jerking that follows engine speed, usually more pronounced as the engine load increases which is not normally felt above 1,500 RPM or 48 km/h (30 mph). | |
| Preliminary | Refer to Symptoms - Engine Controls . |
| Ignition System | Inspect the spark plugs for the following conditions: Insulation cracks Wear Improper gap Burned electrodes Heavy deposits The ignition system for moisture, dust, cracks, burns, etc. |
| Engine Mechanical | Perform a cylinder compression check. Refer to Engine Compression Test in Engine Mechanical. Inspect the engine for the following: Improper valve timing Worn rocker arms-Refer to Valve Rocker Arm and Valve Lash Adjuster Cleaning and Inspection in Engine Mechanical. Worn camshaft lobes-Refer to Camshafts Cleaning and Inspection in Engine Mechanical. Broken or weak valve springs-Refer to Upper Engine Noise, Regardless of Engine Speed in Engine Mechanical. Inspect the intake and exhaust manifold passages for casting flash. |
| Fuel System | Test the fuel pressure. Refer to Fuel System Diagnosis . Inspect for water contamination in the fuel. Refer to Alcohol/Contaminants-in-Fuel Diagnosis (with Special Tool) or Alcohol/Contaminants-in-Fuel Diagnosis (without Special Tool) . Perform the fuel injector coil test. Refer to Fuel Injector Coil Test . |
Cuts Out, Misses
Poor Fuel Economy
| Inspections | Action |
|---|---|
| DEFINITION: Fuel economy, as measured by an actual road test, is noticeably lower than expected. | |
| Preliminary | Refer to Symptoms - Engine Controls . Inspect the air cleaner element, or the filter, for dirt or being plugged. Visually and physically inspect the vacuum hoses for splits, kinks, and proper connections as shown on the Vehicle Emission Control Information label. Discuss the driving habits with the owner for the following items: The A/C is ON full time, or the defroster mode is ON The tires for being at the correct air pressure The wheel and tires are the correct size Excessively heavy loads being carried Aggressive driving habits Suggest to the owner to fill the fuel tank and to inspect the fuel economy. Suggest to the driver to refer to Important Facts on Fuel Economy in the owner manual. |
| Fuel System | Inspect the fuel type, quality, and alcohol content. Refer to Alcohol/Contaminants-in-Fuel Diagnosis (with Special Tool) or Alcohol/Contaminants-in-Fuel Diagnosis (without Special Tool) . Test the fuel pressure. Refer to Fuel System Diagnosis . |
| Ignition System | Inspect the spark plugs. Remove the spark plugs and check for the following: Wet plugs Cracks Wear Improper gap Burned electrodes Heavy deposits Refer to Spark Plug Inspection . Inspect for an open ignition control (IC) circuit. Inspect the knock sensor (KS) system operation. |
| Cooling System | Inspect the engine coolant level. Inspect the engine thermostat for always being open or for the wrong heat range. |
| Additional | Inspect the transmission shift pattern. Refer to Symptoms - Automatic Transmission in Automatic Transmission - 4L60-E. Inspect the torque converter clutch (TCC) operation. Refer to Torque Converter Diagnosis Procedure in Automatic Transmission - 4L60-E. Inspect for proper calibration of the speedometer. Inspect for dragging brakes. Refer to Diagnostic Starting Point - Hydraulic Brakes in Hydraulic Brakes. |
Poor Fuel Economy
Poor Fuel Fill Quality
| Conditions | Causes |
|---|---|
| Difficult to fill | Check valve stuck closed Fill limiter vent valve stuck closed Evaporative emission (EVAP) canister restricted EVAP vent valve stuck closed Restricted vapor lines High reid vapor pressure or high fuel temperature Fuel filler hose is pinched or kinked Ignition ON |
| Over fill | Pressure relief valve in fill limiter vent valve stuck open Pressure relief valve in fill limiter vent valve is leaking Fill limiter vent valve stuck open Fill limiter vent valve is leaking |
| Premature shut-off of the fuel dispensing nozzle | Fill limiter vent valve stuck closed EVAP canister restricted EVAP vent valve stuck closed Restricted vapor lines High reid vapor pressure or high fuel temperature Ignition ON |
| Fuel Spitback | Check valve stuck open Check valve stuck closed Check valve leaking High reid vapor pressure or high fuel temperature |
| Liquid to EVAP canister | Fill limiter vent valve stuck open Fill limiter vent valve leaking |
| Liquid leak to ground | Pressure relief valve in fill limiter vent valve stuck open, or leaking Fuel filler hose loose or torn Fill limiter vent valve stuck open |
| Fuel Odor | Pressure relief in fuel limiter vent valve stuck open, or leaking Saturated EVAP canister |
Poor Fuel Fill Quality
Rough, Unstable, or Incorrect Idle and Stalling
| Inspections | 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. | |
| Preliminary | Refer to Symptoms - Engine Controls . |
| Sensor | Inspect the heated oxygen sensor (HO2S). Check for silicon contamination from fuel or improperly used sealant. The sensor will have a white powdery coating. The sensor will result in a high but false signal voltage, or rich exhaust indication. The control module will reduce the amount of fuel delivered to the engine causing a severe driveability condition. Inspect the engine coolant temperature (ECT) sensor using the 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 degrees more than or less than the ambient air temperature on a cold engine, test for a high resistance in the coolant sensor circuit or the sensor itself. Inspect the manifold absolute pressure (MAP) sensor response and accuracy. |
| Fuel System | Test the fuel pressure. Refer to Fuel System Diagnosis . Inspect to determine if a rich or lean system causes the condition. Drive the vehicle at the speed of the complaint. Monitoring the fuel trim will help identify the condition. Lean-The long term fuel trim is more than 150. Rich-The long term fuel trim is less than 115. Perform the fuel injector balance test. Refer to Fuel Injector Balance Test with Tech 2 . Test the fuel injector driver circuit. Disconnect the injector harness connector at the injectors. Connect an injector test lamp between the terminals of each injector connector and note the lamp while cranking. If the test lamp fails to blink at any connector, it is a faulty injector drive circuit harness, connector, or terminal. Perform the fuel injector coil test. Refer to Fuel Injector Coil Test . Inspect the evaporative emission (EVAP) control system. Refer to Evaporative Emission (EVAP) Control System Description . |
| Ignition System | Inspect the overall ignition system Inspect for the following conditions: Wet plugs Cracks Wear Improper gap Burned electrodes Blistered insulators Heavy deposits Refer to Spark Plug Inspection . |
| Additional | Inspect for vacuum leaks. Vacuum leaks can cause a higher than normal idle and low idle air control (IAC) counts. Inspect the control module grounds for being clean, tight, and in their proper locations. Observe the scan tool to determine if the control module is receiving an A/C signal. Refer to HVAC Compressor Clutch Does Not Engage or HVAC Compressor Clutch Does Not Disengage in HVAC Systems-Manual. If a condition exists with the A/C ON, inspect the A/C system operation. Inspect the battery cables and ground straps for being clean and secure. Inspect the crankcase ventilation valve for proper operation by placing a finger over the inlet hole in the valve end several times. The valve should snap back. If not, replace the valve. Refer to Crankcase Ventilation System Inspection/Description in Engine Mechanical. |
| Engine Mechanical | Inspect for the following: Broken motor mounts-Refer to Engine Mount Inspection in Engine Mechanical. Improper valve timing Low compression-Refer to Engine Compression Test in Engine Mechanical. Worn rocker arms-Refer to Valve Rocker Arm and Valve Lash Adjuster Cleaning and Inspection in Engine Mechanical. Broken or weak valve springs Worn camshaft lobes-Refer to Camshafts Cleaning and Inspection in Engine Mechanical. |
Rough, Unstable, or Incorrect Idle and Stalling
Dieseling, Run-On
| Inspections | Action |
|---|---|
| DEFINITION: The engine continues to run when you turn the key OFF, but runs very roughly. If the engine runs smoothly, test the ignition switch and adjustment. | |
| Preliminary | Refer to Symptoms - Engine Controls . |
| Fuel System | Inspect the evaporative emission (EVAP) system and fuel tank venting. Inspect the fuel injectors for leakage. Refer to Fuel System Diagnosis Perform a fuel system diagnosis. Refer to Fuel System Diagnosis . |
Dieseling, Run-On
Backfire
| Inspections | Action |
|---|---|
| Definition: The fuel ignites in the intake manifold, or in the exhaust system, making a loud popping noise. | |
| Preliminary | Refer to Symptoms - Engine Controls . |
| Ignition System | Inspect the ignition system. |
| Engine Mechanical | Inspect the engine for the following the items: Engine compression-Refer to Engine Compression Test in Engine Mechanical. Improper valve timing Manifold gaskets Sticking or leaking valves Inspect the intake and exhaust system for fresh air entering the exhaust upstream of the catalytic converter or restrictions. Refer to Symptoms - Engine Exhaust in Engine Exhaust. |
| Fuel System | Inspect the fuel system. Refer to Fuel System Diagnosis . Perform the fuel injector balance test. Refer to Fuel Injector Balance Test with Tech 2 . |
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 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 heated oxygen sensor (HO2S) Heater Test indicates YES, all of the oxygen sensor heaters have been diagnosed. If the vehicle has 4 heated oxygen sensors, all 4 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
- EGR system
- Fuel delivery system
- Heated catalyst monitoring
- Misfire monitoring
- Oxygen sensor system (O2S or HO2S)
- Oxygen sensor heater system (HO2S heater)
- 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.