Intermittent Conditions
| Inspections | Action |
|---|---|
| DEFINITION: The condition is not currently present but is indicated in DTC history. OR There is a customer concern, but the symptom cannot currently be duplicated, if the condition is not DTC related. | |
| Preliminary | The fault must be present to locate a condition using the DTC table. If a condition is intermittent, the use of DTC tables may result in the replacement of good parts. Inspect the engine control system grounds for being clean, tight, and in the correct locations. Refer to Engine Controls Schematics . Ensure the resistance between the engine control module (ECM) housing and the battery negative cable is less than 0.5 ohms. |
| Visual/Physical | This step is an important aid for locating a condition without extensive testing. Perform a thorough inspection of the following items: Inspect the wiring harness for damage. Inspect for a mis-routed harness that is too close to high voltage or high current devices such as the following: Secondary ignition components Motors and generators - These components may induce electrical noise on a circuit which can interfere with normal circuit operation. Inspect the vacuum hoses for splits or kinks. Verify that the connections and routing are as shown on the Vehicle Emission Control Information label. Refer to Emission Hose Routing Diagram . Inspect for air leaks at the throttle body mounting and intake manifold sealing surfaces. Inspect for air leaks at the air cleaner outlet resonator and verify the correct installation of the mass air flow (MAF) sensor. Refer to Mass Air Flow (MAF)/Intake Air Temperature (IAT) Sensor Replacement . Verify that the ECM grounds and the body grounds are clean, tight, and in the correct locations. Ensure the resistance between the ECM housing and the battery negative cable is less than 0.5 ohms. Verify that the ECM and ECM bracket fasteners are at the correct torque. Verify the battery connections are clean and tight. Test the charging system for the correct operation. Refer to Symptoms - Engine Electrical in Engine Electrical. |
| Harness/Connector Inspection | Many intermittent conditions occur with harness/connector movement caused by vibration, engine torque, rough pavement, or component operation. Refer to Testing for Electrical Intermittents in Wiring Systems. Excessive circuit resistance can cause a component to be inoperative. If a component does not respond to a scan tool command, test the related circuits for excessive resistance. Refer to Testing for Continuity in Wiring Systems. |
| Intermittent malfunction indicator lamp (MIL) with NO DTCs | The following conditions may cause an intermittent malfunction indicator lamp (MIL) and no DTCs: Electromagnetic interference (EMI) caused by a malfunctioning relay, ECM controlled solenoid, or switch The incorrect installation of non-factory or aftermarket add-on accessories such as cellular phones, alarms, lights, or radio equipment The MIL control circuit is intermittently shorted to ground. The ECM grounds are loose. |
| Temperature Sensitivity | An intermittent condition may occur only when the component is cold or only when the component is hot. The heat that affects the circuit can be engine generated or due to a poor connection in the circuit or a high electrical load. Information from the customer may help to determine if the condition follows a pattern that is temperature related. The Freeze Frame/Failure Records or Snapshot data may help with this type of intermittent condition, where applicable. If the intermittent is related to heat, review the data for a relationship with the following: High ambient temperatures Underhood/engine generated heat Circuit generated heat due to a poor connection or high electrical load Higher than normal load conditions (towing, etc.) If the intermittent is related to cold, review the data for the following: Low ambient temperatures - In extremely low temperatures, ice may form in a connection or component. Inspect for water intrusion. The condition only occurs on a cold start. The condition goes away when the engine warms up. |
| Duplicating Failure Conditions | Attempt to duplicate and/or capture the failure conditions. Freeze Frame/Failure Records data contains the conditions that are present when a DTC sets. Operate the vehicle within the same conditions that you observed in the Freeze Frame/Failure Records. 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. The scan tool can be set up to take a snapshot of parameters. 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 individually or in a combination with other parameters for comparison. The Snapshot can be triggered manually at the time the symptom is noticed, or set up in advance to trigger when the DTC sets. An abnormal value captured in the recorded data may point to a system or component that requires further investigation. Refer to scan tool user instructions for more information on the Snapshot function. An alternate method is to drive the vehicle with a DMM connected to a suspected circuit. An abnormal reading on the DMM when the problem occurs may help you locate the problem. |
| Additional Inspections | Some electrical components and circuits are sensitive to EMI or other types of electrical noise. Inspect for the following conditions: A mis-routed harness that is too close to high voltage and high current devices such as secondary ignition components, motors, generator - These components may induce electrical noise on a circuit that could interfere with normal circuit operation. Electrical system interference caused by a relay, ECM driven solenoid, or switch - The component can cause a sharp electrical surge. Normally, the condition occurs when the component is operating. Incorrect installation of non-factory, aftermarket, add-on accessories such as 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 or resistor. Test the generator for a faulty rectifier bridge that may allow AC noise into the electrical system. Refer to Symptoms - Engine Electrical in Engine Electrical. |
Intermittent Conditions
Hard Start
| Inspections | Action |
|---|---|
| DEFINITION: Engine cranks OK, but does not start for a long time. Does eventually run, or may start but immediately dies. | |
| Preliminary | Refer to Important Preliminary Inspections Before Starting in Symptoms - Engine Controls . Inspect the engine control system grounds for being clean, tight, and in the correct locations. Refer to Engine Controls Schematics . Ensure the resistance between the engine control module (ECM) housing and the battery negative cable is less than 0.5 ohms. Verify that the ECM and ECM bracket fasteners are at the correct torque. Search for service bulletins that may address this condition. |
| Sensor/System | IMPORTANT: Allow the engine to cool before performing this test. Inspect the engine coolant temperature (ECT) sensor for being skewed in value. Compare the ECT sensor value to the intake air temperature (IAT) sensor value on a cold engine. The ECT and IAT sensor values should be within +/- 3°C (5°F). If the ECT sensor is out of range with the IAT sensor, test the resistance of the ECT sensor. Refer to Temperature vs Resistance - Engine Coolant Temperature (ECT) Sensor for resistance specifications. Replace the ECT sensor if the resistance is not within the specification. Refer to Engine Coolant Temperature (ECT) Sensor Replacement . If the sensor is within the specification, repair the high resistance in the ECT signal circuit. Inspect the crankshaft position (CKP) sensor for the correct resistance. The sensor resistance may be out of range after a hot soak. Measure that the resistance remains within 700-1,200 ohms at all temperatures. |
| Fuel System | Test the fuel pump relay operation. The fuel pump should turn ON for 2 seconds when the ignition is turned ON. Refer to Fuel Pump Electrical Circuit Diagnosis . Test for incorrect fuel pressure. Refer to Fuel System Diagnosis . Test for a restricted fuel filter. Refer to Fuel System Diagnosis . Test for leaking fuel injectors. Refer to Fuel System Diagnosis . Test for plugged or restricted injectors. Refer to Fuel Injector Balance Test with Special Tool . Test for a contaminated fuel condition. Refer to Alcohol/Contaminants-in-Fuel Diagnosis (w/o Special Tool) or Alcohol/Contaminants-in-Fuel Diagnosis (w/Special Tool) . |
| Ignition System | Inspect for the correct installation of the ignition coil seals. Incorrect installation may allow water to enter the spark plug area. Inspect for moisture and corrosion. Test the ignition voltage output with J 26792 Spark Tester. See Special Tools . If you suspect an ignition system condition exists, refer to Electronic Ignition (EI) System Diagnosis . Remove the spark plugs and inspect for the following conditions: Correct heat range Wet plugs Cracks Wear Improper gap Burned electrodes Heavy deposits Refer to the following procedures: Spark Plug Replacement Ignition System Specifications Spark Plug Inspection If the spark plugs are gas, coolant, or oil fouled, determine the cause before replacing the spark plugs. Refer to the following procedures: For diagnosis of a rich condition, refer to DTC P2178 or P2180 , DTC P2188 or P2190 , and DTC P2196 or P2198 . For diagnosis of coolant contaminated spark plugs, refer to Loss of Coolant in Engine Cooling. For diagnosis of oil fouled spark plugs, refer to Oil Consumption Diagnosis in Engine Mechanical - 3.6L (LY7). Inspect the spark plug boots and terminals for burning or micro-arcing, corrosion, and damage to the insulation. |
| Engine Mechanical | Inspect for the following engine mechanical conditions: Excessive oil in combustion chamber or leaking valve seals Low cylinder compression Sticking or leaking valves Worn camshaft lobes Camshaft timing Broken valve springs Excessive carbon buildup in the combustion chambers. Clean the chambers with top engine cleaner. Follow the instructions on the can. For more information, refer to the following procedures in Engine Mechanical - 3.6L (LY7): Oil Consumption Diagnosis Engine Compression Test Camshaft Timing Drive Chain Alignment Diagram (With Primary Roller Chain) or Camshaft Timing Drive Chain Alignment Diagram (W/Primary (IT) Inverted Tooth Chain) Setting Camshaft Timing Symptoms - Engine Mechanical Inspect the following components for incorrect basic engine parts: Camshafts Cylinder heads Pistons, connecting rods, or bearings. Refer to the following procedures in Engine Mechanical - 3.6L (LY7): Camshaft Timing Drive Components Cleaning and Inspection Camshaft Cleaning and Inspection Cylinder Head Cleaning and Inspection Piston, Connecting Rod, and Bearings Cleaning and Inspection |
| IMPORTANT |
|---|
| Allow the engine to cool before performing this test. |
Hard Start
Surges/Chuggles
| Inspections | Action |
|---|---|
| DEFINITION: Engine power variation under steady throttle or cruise. Feels like the vehicle speeds up and slows down without a change in the accelerator pedal position. | |
| Preliminary | Refer to Important Preliminary Inspections Before Starting in Symptoms - Engine Controls . Search for bulletins. Inspect the engine control system grounds for being clean, tight, and in the correct locations. Refer to Engine Controls Schematics . Ensure the resistance between the engine control module (ECM) housing and the battery negative cable is less than 0.5 ohms. Verify that the ECM and ECM bracket fasteners are at the correct torque. Ensure that the driver understands the operation of the transmission torque converter clutch (TCC) and A/C compressor operation as explained in the owner's manual. Inform the customer how the TCC and the A/C clutch operates. |
| Fuel System | Test for incorrect fuel pressure. Refer to Fuel System Diagnosis . Test for a restricted fuel filter. Refer to Fuel System Diagnosis . Test for a contaminated fuel condition. Refer to Alcohol/Contaminants-in-Fuel Diagnosis (w/o Special Tool) or Alcohol/Contaminants-in-Fuel Diagnosis (w/Special Tool) . Verify that each injector harness is connected to the correct injector/cylinder according to the firing order. Test the fuel injectors. Refer to Fuel Injector Coil Test . Test the items that cause an engine to run rich. For a rich condition, refer to DTC P2178 or P2180 and DTC P2188 or P2190 Test the items that can cause an engine to run lean. For a lean condition, refer to DTC P2177 or P2179 and DTC P2187 or P2189 |
| Ignition System | Inspect for the correct installation of the ignition coil seals. Incorrect installation may allow water to enter the spark plug area. Inspect for moisture and corrosion. Test for proper ignition voltage output with a J 26792 Spark Tester. See Special Tools . If you suspect an ignition system condition exists, refer to Electronic Ignition (EI) System Diagnosis . Remove the spark plugs and inspect for the following conditions: Correct heat range Wet plugs Cracks Wear Improper gap Burned electrodes Heavy deposits Refer to the following procedures: Spark Plug Replacement Ignition System Specifications Spark Plug Inspection If the spark plugs are gas, coolant or oil fouled, determine the cause before replacing the spark plugs. Refer to the following procedures: Test the items that cause an engine to run rich. For a rich condition, refer to DTC P2178 or P2180 and DTC P2188 or P2190 . For diagnosis of coolant contaminated spark plugs, refer to Loss of Coolant in Engine Cooling. For diagnosis of oil fouled spark plugs, refer to Oil Consumption Diagnosis in Engine Mechanical - 3.6L (LY7). Inspect the crankshaft position (CKP) sensor for the correct resistance. The sensor resistance may be out of range after a hot soak. Measure that the resistance remains within 700-1,200 ohms at all temperatures. Inspect the spark plug boots and terminals for burning or micro-arcing, corrosion, and damage to the insulation. |
| Additional | Inspect the vacuum hoses for splits and kinks. Verify that the connections and routing are as shown on the Vehicle Emission Control Information Label, refer to Emission Hose Routing Diagram . Inspect for a condition with the camshaft actuator system. A camshaft actuator that is stuck in the full advance or retard position may cause this symptom. Refer to DTC P0011, P0014, P0021, or P0024 . Test the TCC operation. A TCC applying too soon can cause the engine to spark knock, surge or chuggle. Refer to Torque Converter Diagnosis Procedure in Automatic Transmission - 5L40-E/4L50-E. Test the A/C clutch for the correct operation. Refer to Symptoms - HVAC Systems - Automatic in HVAC Systems - Automatic. |
Surges/Chuggles
Lack of Power, Sluggishness, or Sponginess
| Inspections | Action |
|---|---|
| DEFINITION: The engine delivers less than expected power. Little increase in speed, or a total lack of acceleration when the accelerator pedal is pushed down part way. | |
| Preliminary | Refer to Important Preliminary Inspections Before Starting in Symptoms - Engine Controls . Search for bulletins. Inspect the engine control system grounds for being clean, tight, and in the correct locations. Refer to Engine Controls Schematics . Ensure the resistance between the engine control module (ECM) housing and the battery negative cable is less than 0.5 ohms. Verify that the ECM and ECM bracket fasteners are at the correct torque. Remove the air filter element and inspect for restrictions. Refer to Air Cleaner Element Replacement . Inspect the intake air duct and air cleaner outlet resonator for the following conditions: Restrictions Improperly installed hoses Leaks Collapsed hoses |
| Fuel System | Test for incorrect fuel system pressure. Refer to Fuel System Diagnosis . Test for a restricted fuel filter. Refer to Fuel System Diagnosis . Test for a contaminated fuel condition. Refer to Alcohol/Contaminants-in-Fuel Diagnosis (w/o Special Tool) or Alcohol/Contaminants-in-Fuel Diagnosis (w/Special Tool) . Test the fuel injectors. Refer to Fuel Injector Coil Test . Test the items that cause an engine to run rich. For a rich condition, refer to DTC P2178 or P2180 and DTC P2188 or P2190 . Test the items that can cause an engine to run lean. For a lean condition, refer to DTC P2177 or P2179 and DTC P2187 or P2189 . |
| Sensor/System | Monitor the knock sensor (KS) system for excessive spark retard activity with a scan tool. Refer to Knock Sensor (KS) System Description , DTC P0327 or P0332 , and DTC P0328 or P0333 . |
| Ignition System | Inspect for the correct installation of the ignition coil seals. Incorrect installation may allow water to enter the spark plug area. Inspect for moisture and corrosion. Test for the correct ignition voltage output with a J 26792 Spark Tester. See Special Tools . If you suspect an ignition system condition exists, refer to Electronic Ignition (EI) System Diagnosis . Remove the spark plugs and inspect for the following conditions: Incorrect heat range Wet plugs Cracks Wear Improper gap Burned electrodes Heavy deposits Refer to the following procedures: Spark Plug Replacement Ignition System Specifications Spark Plug Inspection If the spark plugs are gas, coolant, or oil fouled, determine the cause before replacing the spark plugs. Refer to the following procedures: Test the items that cause an engine to run rich. For a rich condition, refer to DTC P2178 or P2180 and DTC P2188 or P2190 . For diagnosis of coolant contaminated spark plugs, refer to Loss of Coolant in Engine Cooling. For diagnosis of oil fouled spark plugs, refer to Oil Consumption Diagnosis in Engine Mechanical - 3.6L (LY7). Inspect the crankshaft position (CKP) sensor for the correct resistance. The sensor resistance may be out of range after a hot soak. Measure that the resistance remains within 700-1,200 ohms at all temperatures. Inspect the spark plug boots and terminals for burning or micro-arcing, corrosion, and damage to the insulation. |
| Engine Mechanical | Inspect for a condition with the camshaft actuator system. A camshaft actuator that is stuck in the full advance or retard position may cause this symptom. Refer to DTC P0011, P0014, P0021, or P0024 . Inspect for the following engine mechanical conditions: Excessive oil in combustion chamber or leaking valve seals Incorrect cylinder compression Sticking or leaking valves Worn camshaft lobes Camshaft timing Broken valve springs Excessive carbon buildup in the combustion chambers - Clean the chambers with top engine cleaner. Follow the instructions on the can. For more information, refer to the following procedures in Engine Mechanical - 3.6L (LY7): Oil Consumption Diagnosis Engine Compression Test Camshaft Timing Drive Chain Alignment Diagram (With Primary Roller Chain) or Camshaft Timing Drive Chain Alignment Diagram (W/Primary (IT) Inverted Tooth Chain) Setting Camshaft Timing Symptoms - Engine Mechanical Inspect the following components for incorrect basic engine parts: Camshafts Cylinder heads Pistons, connecting rods, or bearings Refer to the following procedures in Engine Mechanical - 3.6L (LY7): Camshaft Timing Drive Components Cleaning and Inspection Camshaft Cleaning and Inspection Cylinder Head Cleaning and Inspection Piston, Connecting Rod, and Bearings Cleaning and Inspection |
| Additional | Inspect the following exhaust system components: The exhaust system for damage The mufflers for heat distress or possible internal failure The catalytic converters for restrictions For more information, refer to Symptoms - Engine Exhaust in Engine Exhaust. Test for the correct operation of the intake manifold runner control solenoid. Refer to Intake Manifold Runner Control System Diagnosis . Test the transmission torque converter clutch (TCC) for the correct operation. Refer to Torque Converter Diagnosis Procedure in Automatic Transmission - 5L40-E/5L50-E. Test for other transmission related faults that might cause the transmission to operate in a default mode. |
Lack of Power, Sluggishness, or Sponginess
Detonation/Spark Knock
| Inspection | Action |
|---|---|
| DEFINITION: A mild to severe ping which usually occurs worse while under acceleration. The engine makes sharp metallic knocks that change with throttle opening. | |
| Preliminary | Refer to Important Preliminary Inspections Before Starting in Symptoms - Engine Controls . Inspect the engine control system grounds for being clean, tight, and in the correct locations. Refer to Engine Controls Schematics . Ensure the resistance between the engine control module (ECM) housing and the battery negative cable is less than 0.5 ohms. Verify that the ECM and ECM bracket fasteners are at the correct torque. If the scan tool readings are normal and there are not any engine mechanical faults, fill the fuel tank with a known high quality fuel that meets the vehicle's minimum octane requirements. Road test the vehicle and re-evaluate the vehicle's performance. |
| Fuel System | Test for incorrect fuel pressure. Refer to Fuel System Diagnosis . Test for a restricted fuel filter. Refer to Fuel System Diagnosis . Test for a contaminated fuel condition. Refer to Alcohol/Contaminants-in-Fuel Diagnosis (w/o Special Tool) or Alcohol/Contaminants-in-Fuel Diagnosis (w/Special Tool) . Test the fuel injectors. Refer to Fuel Injector Coil Test . Test the items that can cause an engine to run lean. For a lean condition, refer to DTC P2177 or P2179 and DTC P2187 or P2189 |
| Sensor/System | Use a scan tool to monitor the knock sensor (KS) system. Refer to Knock Sensor (KS) System Description . |
| Ignition System | Ensure that the spark plugs are the correct heat range. Refer to Ignition System Specifications . |
| Engine Cooling System | Test for obvious overheating conditions. Test or inspect for the following conditions: Low engine coolant level Incorrect engine coolant Restricted air flow to the radiator or restricted coolant flow through the radiator Engine coolant leaks Refer to the following procedures in Engine Cooling: Draining and Filling Cooling System Engine Overheating |
| Engine Mechanical | Inspect for the following engine mechanical conditions: Excessive oil in combustion chambers and for leaking valve seals High cylinder compression Incorrect camshaft timing Excessive carbon buildup in the combustion chambers - Clean the chambers using top engine cleaner. Follow the instructions on the can. For more information, refer to the following procedures in Engine Mechanical - 3.6L (LY7): Oil Consumption Diagnosis Engine Compression Test Camshaft Timing Drive Chain Alignment Diagram (With Primary Roller Chain) or Camshaft Timing Drive Chain Alignment Diagram (W/Primary (IT) Inverted Tooth Chain) Setting Camshaft Timing Symptoms - Engine Mechanical Inspect the following components for incorrect basic engine parts: Camshafts Cylinder heads Pistons, connecting rods, or bearings Refer to the following procedures in Engine Mechanical - 3.6L (LY7): Camshaft Timing Drive Components Cleaning and Inspection Camshaft Cleaning and Inspection Cylinder Head Cleaning and Inspection Piston, Connecting Rod, and Bearings Cleaning and Inspection |
| Additional | Test the transmission torque converter clutch (TCC) for the correct operation. Applying the TCC too soon can cause the engine to spark knock. Refer to Torque Converter Diagnosis Procedure in Automatic Transmission - 5L40-E/5L50-E. |
Detonation/Spark Knock
Hesitation, Sag, Stumble
| Inspections | Action |
|---|---|
| DEFINITION: Momentary lack of response as the accelerator is pushed down. This condition can occur at any vehicle speed. This condition is usually more pronounced when first trying to make the vehicle move, as from a stop sign. This condition may cause the engine to stall if severe enough. | |
| Preliminary | Refer to Important Preliminary Inspections Before Starting in Symptoms - Engine Controls . Search for bulletins. Inspect the engine control system grounds for being clean, tight, and in the correct locations. Refer to Engine Controls Schematics . Ensure the resistance between the engine control module (ECM) housing and the battery negative cable is less than 0.5 ohms. Verify that the ECM and ECM bracket fasteners are at the correct torque. Remove the air filter element and inspect for restrictions. Refer to Air Cleaner Element Replacement . Inspect the intake air duct and air cleaner outlet resonator for the following conditions: Restrictions Improperly installed hoses Leaks Collapsed hoses |
| Sensor/System | Test the heated oxygen sensors (HO2S). The HO2S should respond quickly to a change in throttle position. If the HO2S does not respond to different throttle positions, inspect for contamination from fuel, silicon, or incorrect use of RTV sealant. The sensors may have a white powdery coating. The coating causes a low, but false, signal voltage, which gives a rich exhaust indication. The ECM reduces the amount of fuel delivered to the engine, causing a driveability condition. Inspect the mass air flow (MAF) sensor for the correct operation. Refer to DTC P0101 . |
| Fuel System | Test for incorrect fuel pressure. Refer to Fuel System Diagnosis . Test for a restricted fuel filter. Refer to Fuel System Diagnosis . Test for a contaminated fuel condition. Refer to Alcohol/Contaminants-in-Fuel Diagnosis (w/o Special Tool) or Alcohol/Contaminants-in-Fuel Diagnosis (w/Special Tool) . Test the fuel injectors. Refer to Fuel Injector Coil Test . Test the items that cause an engine to run rich. For a rich condition, refer to DTC P2178 or P2180 and DTC P2188 or P2190 . Test the items that can cause an engine to run lean. For a lean condition, refer to DTC P2177 or P2179 and DTC P2187 or P2189 . |
| Ignition System | Inspect for the correct installation of the ignition coil seals. Incorrect installation may allow water to enter the spark plug area. Inspect for moisture and corrosion. Test for the correct ignition voltage output with a J 26792 Spark Tester. See Special Tools . If you suspect an ignition system condition exists, refer to Electronic Ignition (EI) System Diagnosis . Remove the spark plugs and inspect for the following conditions: Incorrect heat range Wet plugs Cracks Wear Improper gap Burned electrodes Heavy deposits Refer to the following procedures: Spark Plug Replacement Ignition System Specifications Spark Plug Inspection If the spark plugs are gas, coolant, or oil fouled, determine the cause before replacing the spark plugs. Refer to the following procedures: Test the items that cause an engine to run rich. For a rich condition, refer to DTC P2178 or P2180 and DTC P2188 or P2190 . For diagnosis of coolant contaminated spark plugs, refer to Loss of Coolant in Engine Cooling. For diagnosis of oil fouled spark plugs, refer to Oil Consumption Diagnosis in Engine Mechanical - 3.6L (LY7). Inspect the crankshaft position (CKP) sensor for the correct resistance. The sensor resistance may be out of range after a hot soak. Measure that the resistance remains within 700-1,200 ohms at all temperatures. Inspect the spark plug boots and terminals for burning or micro-arcing, corrosion, and damage to the insulation. |
| Engine Cooling System | Test the engine thermostat for the correct operation and heat range. Refer to Thermostat Diagnosis in Engine Cooling. |
| Additional | Inspect for a condition with the camshaft actuator system. A camshaft actuator that is stuck in the full advance or retard position may cause this symptom. Refer to DTC P0011, P0014, P0021, or P0024 . Test for the correct operation of the intake manifold runner control solenoid. Refer to Intake Manifold Runner Control System Diagnosis . Test the generator output voltage. Refer to Symptoms - Engine Electrical in Engine Electrical. Repair the charging system if the generator output voltage is less than 9 volts or more than 16 volts. |
Hesitation, Sag, Stumble
Cuts Out, Misses
| Inspections | Action |
|---|---|
| DEFINITION: A steady pulsation or jerking that follows engine speed, which is usually more pronounced as the engine load increases. This condition is not normally felt above 1,500 RPM or 48 km/h (30 mph). The exhaust has a steady spitting sound at idle or at low speed. | |
| Preliminary | Refer to Important Preliminary Inspections Before Starting in Symptoms - Engine Controls . Search for bulletins. Inspect the engine control system grounds for being clean, tight, and in the correct locations. Refer to Engine Controls Schematics . Ensure the resistance between the engine control module (ECM) housing and the battery negative cable is less than 0.5 ohms. Verify that the ECM and ECM bracket fasteners are at the correct torque. Remove the air filter element and inspect for restrictions. Refer to Air Cleaner Element Replacement . Inspect the intake air duct and air cleaner outlet resonator for the following conditions: Restrictions Improperly installed hoses Leaks Collapsed hoses |
| Fuel System | Test for incorrect fuel pressure. Refer to Fuel System Diagnosis . Test for a restricted fuel filter. Refer to Fuel System Diagnosis . Inspect the fuel system. Refer to Fuel System Diagnosis . Test for a contaminated fuel condition. Refer to Alcohol/Contaminants-in-Fuel Diagnosis (w/o Special Tool) or Alcohol/Contaminants-in-Fuel Diagnosis (w/Special Tool) . Test the fuel injectors. Refer to Fuel Injector Coil Test . Test the items that cause an engine to run rich. For a rich condition, refer to DTC P2178 or P2180 and DTC P2188 or P2190 . Test the items that can cause an engine to run lean. For a lean condition, refer to DTC P2177 or P2179 and DTC P2187 or P2189 . |
| Sensor/System | Monitor the knock sensor (KS) system for excessive spark retard activity with a scan tool. Refer to Knock Sensor (KS) System Description , DTC P0327 or P0332 , and DTC P0328 or P0333 . |
| Ignition System | Inspect for the correct installation of the ignition coil seals. Incorrect installation may allow water to enter the spark plug area. Inspect for moisture and corrosion. Test for proper ignition voltage output with a J 26792 Spark Tester. See Special Tools . If you suspect an ignition system condition, refer to Electronic Ignition (EI) System Diagnosis . Remove the spark plugs and inspect for the following conditions: Incorrect heat range Wet plugs Cracks Wear Improper gap Burned electrodes Heavy deposits Refer to the following procedures: Spark Plug Replacement Ignition System Specifications Spark Plug Inspection If the spark plugs are gas, coolant, or oil fouled, determine the cause before replacing the spark plugs. Refer to the following procedures: Test the items that cause an engine to run rich. For a rich condition, refer to DTC P2178 or P2180 and DTC P2188 or P2190 . For diagnosis of coolant contaminated spark plugs, refer to Loss of Coolant in Engine Cooling. For diagnosis of oil fouled spark plugs, refer to Oil Consumption Diagnosis in Engine Mechanical - 3.6L (LY7). Inspect the spark plug boots and terminals for burning or micro-arcing, corrosion, and damage to the insulation. Inspect the crankshaft position (CKP) sensor for the correct resistance. The sensor resistance may be out of range after a hot soak. Measure that the resistance remains within 700-1,200 ohms at all temperatures. |
| Engine Mechanical | Inspect for a condition with the camshaft actuator system. A camshaft actuator that is stuck in the full advance or retard position may cause this symptom. Refer to DTC P0011, P0014, P0021, or P0024 . Inspect for the following engine mechanical conditions: Excessive oil in combustion chamber or leaking valve seals Incorrect cylinder compression Sticking or leaking valves Worn camshaft lobes Camshaft timing Broken valve springs Excessive carbon buildup in the combustion chambers - Clean the chambers with top engine cleaner. Follow the instructions on the can. For more information, refer to the following procedures in Engine Mechanical - 3.6L (LY7): Oil Consumption Diagnosis Engine Compression Test Camshaft Timing Drive Chain Alignment Diagram (With Primary Roller Chain) or Camshaft Timing Drive Chain Alignment Diagram (W/Primary (IT) Inverted Tooth Chain) Setting Camshaft Timing Symptoms - Engine Mechanical Inspect the following components for incorrect basic engine parts: Camshafts Cylinder heads Pistons, connecting rods, or bearings. Refer to the following procedures in Engine Mechanical - 3.6L (LY7): Camshaft Timing Drive Components Cleaning and Inspection Camshaft Cleaning and Inspection Cylinder Head Cleaning and Inspection Piston, Connecting Rod, and Bearings Cleaning and Inspection |
| Additional | Inspect the following exhaust system components: The exhaust system for damage The mufflers for heat distress or possible internal failure The three-way catalytic converters for restrictions For more information, refer to Symptoms - Engine Exhaust . Electromagnetic interference (EMI) on the CKP sensor signal circuits can cause an engine misfire condition. You can usually detect EMI with a scan tool by monitoring the engine speed parameter. A sudden increase in the engine speed parameter, with little change in actual engine speed indicates that EMI is present. Inspect for high voltage components near the ignition control circuits if a condition exists. Also, inspect the engine ground shield of the CKP sensor circuits. |
Cuts Out, Misses
Poor Fuel Economy
| Inspections | Action |
|---|---|
| DEFINITION: Fuel economy, as measured by an actual road test, is noticeably lower than expected. Also, the fuel economy is noticeably lower than it was on this vehicle at one time, as previously shown by an actual road test. | |
| Preliminary | Refer to Important Preliminary Inspections Before Starting in Symptoms - Engine Controls . Search for bulletins. Inspect the engine control module (ECM) grounds for being clean, tight, and in the correct locations. Refer to Engine Controls Schematics . Verify that the ECM and ECM bracket fasteners are at the correct torque. Verify the owner's driving habits, by asking the following questions: Is the A/C or the Defroster mode ON full time? Are the tires at the correct pressure? Is there excessively heavy loads being carried? Is the acceleration rate too much, too often? Is the vehicle used for towing? Remove the air filter element and inspect for restrictions. Refer to Air Cleaner Element Replacement . Inspect the intake air duct and air cleaner outlet resonator for the following conditions: Restrictions Improperly installed hoses Leaks Collapsed hoses |
| Fuel System | Determine 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 (w/o Special Tool) or Alcohol/Contaminants-in-Fuel Diagnosis (w/Special Tool) . Test for incorrect fuel pressure. Refer to Fuel System Diagnosis . Test for a restricted fuel filter. Refer to Fuel System Diagnosis . Verify that each injector harness is connected to the correct injector/cylinder according to the firing order. Test the fuel injectors. Refer to Fuel Injector Coil Test . Inspect for foreign material accumulation in the throttle bore, coking on the throttle valve, or on the throttle shaft. Refer to Throttle Body Service . Also inspect for throttle body tampering. Test the items that cause an engine to run rich. For a rich condition, refer to DTC P2178 or P2180 and DTC P2188 or P2190 . |
| Sensor/System | Inspect the air intake system and the crankcase for air leaks. Test the crankcase ventilation system for proper operation. Refer to Crankcase Ventilation System Inspection/Diagnosis in Engine Mechanical - 3.6L (LY7). Test for correct calibration of the speedometer. Incorrect tire size or axle ratios can affect speedometer calibration and vehicle mileage. Refer to MPH (Km/h) Indicator Inoperative or Symptoms - Instrument Panel, Gages and Console in Instrument Panel, Gages, and Console. Monitor the knock sensor (KS) system for excessive spark retard activity with a scan tool. Refer to Knock Sensor (KS) System Description , DTC P0327 or P0332 , and DTC P0328 or P0333 . |
| Ignition System | Inspect for the correct installation of the ignition coil seals. Incorrect installation may allow water to enter the spark plug area. Inspect for moisture and corrosion. Test for the correct ignition voltage output with a J 26792 Spark Tester. See Special Tools . If you suspect an ignition system condition, refer to Electronic Ignition (EI) System Diagnosis . Remove the spark plugs and inspect for the following conditions: Incorrect heat range Wet plugs Cracks Wear Improper gap Burned electrodes Heavy deposits Refer to the following procedures: Spark Plug Replacement Ignition System Specifications Spark Plug Inspection If the spark plugs are gas, coolant, or oil fouled, determine the cause before replacing the spark plugs. Refer to the following procedures: Test the items that cause an engine to run rich. For a rich condition, refer to DTC P2178 or P2180 and DTC P2188 or P2190 . For diagnosis of coolant contaminated spark plugs, refer to Loss of Coolant in Engine Cooling. For diagnosis of oil fouled spark plugs, refer to Oil Consumption Diagnosis in Engine Mechanical - 3.6L (LY7). Inspect the spark plug boots and terminals for burning or micro-arcing, corrosion, and damage to the insulation. |
| Engine Cooling System | Inspect the engine coolant level for being low. Refer to Draining and Filling Cooling System in Engine Cooling. Test the engine thermostat. Verify the correct operation and heat range. Refer to Thermostat Diagnosis in Engine Cooling. |
| Engine Mechanical | Inspect for the following engine mechanical conditions: Excessive oil in the combustion chamber or leaking valve seals Incorrect cylinder compression Sticking or leaking valves Worn camshaft lobes Camshaft timing Broken valve springs Excessive carbon buildup in the combustion chambers - Clean the chambers with top engine cleaner. Follow the instructions on the can. For more information, refer to the following procedures in Engine Mechanical - 3.6L (LY7): Oil Consumption Diagnosis Engine Compression Test Camshaft Timing Drive Chain Alignment Diagram (With Primary Roller Chain) or Camshaft Timing Drive Chain Alignment Diagram (W/Primary (IT) Inverted Tooth Chain) Setting Camshaft Timing Symptoms - Engine Mechanical Inspect the following components for incorrect basic engine parts: Camshafts Cylinder heads Pistons, connecting rods, or bearings Refer to the following procedures in Engine Mechanical - 3.6L (LY7): Camshaft Timing Drive Components Cleaning and Inspection Camshaft Cleaning and Inspection Cylinder Head Cleaning and Inspection Piston, Connecting Rod, and Bearings Cleaning and Inspection |
| Additional | Inspect the vacuum hoses for splits and kinks. Verify that the connections and routing are as shown on the Vehicle Emission Control Information Label. Refer to Emission Hose Routing Diagram . Test the transmission torque converter clutch (TCC). The scan tool should indicate a drop in engine speed, when the system commands the TCC ON. Refer to Torque Converter Diagnosis Procedure in Automatic Transmission - 5L40-E/5L50-E. Inspect the following exhaust system components: The exhaust system for damage The mufflers for heat distress or possible internal failure The three-way catalytic converters for restrictions For more information, refer to Symptoms - Engine Exhaust in Engine Exhaust. Electromagnetic interference (EMI) on the crankshaft position (CKP) sensor signal circuits can cause an engine misfire condition. You can usually detect EMI with a scan tool by monitoring the engine speed parameter. A sudden increase in the engine speed parameter, with little change in actual engine speed, indicates that EMI is present. Inspect for high voltage components near the ignition control circuits if a condition exists. Also, inspect the engine ground shield of the CKP sensor circuits. Inspect the brake system, including the parking brake, for dragging or incorrect operation. Refer to Symptoms - Hydraulic Brakes in Hydraulic Brakes. Ensure that the vehicle operator does not drive with a foot on the brake pedal. |
Poor Fuel Economy
Poor Fuel Fill Quality
| Condition | Causes |
|---|---|
| DEFINITION: Difficulty when refueling the vehicle. | |
| Difficult to fill | Inspect for the following conditions: Restricted vent lines The evaporative emission (EVAP) vent valve is stuck closed High fuel temperature A condition with the internal components of the fuel tank assembly. For more information, refer to: Fuel Hose/Pipes Routing Diagram Evaporative Emissions (EVAP) Hose Routing Diagram Fuel System Description Evaporative Emission (EVAP) Control System Description |
| Over fill | A condition with the internal components of the fuel tank assembly. Refer to Fuel System Description . |
| Pre-mature shut-off of the fuel dispensing nozzle | Inspect for the following conditions: The EVAP vent valve is stuck closed Restricted vent lines High Reid vapor pressure or high fuel temperature A condition with the internal components of the fuel tank assembly For more information, refer to Fuel System Description and Evaporative Emission (EVAP) Control System Description . |
| Fuel Spitback | Inspect the fuel system for the following conditions: High Reid vapor pressure or high fuel temperature A condition with the internal components of the fuel tank assembly. For more information, refer to Fuel System Description . |
| Fuel Odor | Inspect for the following conditions: Saturated EVAP canister - Refer to Evaporative Emission (EVAP) Control System Description . A condition with the internal components of the fuel tank assembly - Refer to Fuel System Description . |
Poor Fuel Fill Quality
Rough, Unstable, or Incorrect Idle and Stalling
| Inspections | Action |
|---|---|
| DEFINITION: The engine runs unevenly at idle. If severe, the engine or the vehicle may shake. Engine idle may vary in speed. Either condition may be severe enough to stall the engine. | |
| Preliminary | Refer to Important Preliminary Inspections Before Starting in Symptoms - Engine Controls . Search for bulletins. Inspect the engine control system grounds for being clean, tight, and in the correct locations. Refer to Engine Controls Schematics . Ensure the resistance between the engine control module (ECM) housing and the battery negative cable is less than 0.5 ohms. Verify that the ECM and ECM bracket fasteners are at the correct torque. Remove the air filter element and inspect for restrictions. Refer to Air Cleaner Element Replacement . Inspect the intake air duct and air cleaner outlet resonator for the following conditions: Restrictions Improperly installed hoses Leaks Collapsed hoses |
| Fuel System | Test for incorrect fuel pressure. Refer to Fuel System Diagnosis . Test for a restricted fuel filter. Refer to Fuel System Diagnosis . Test for a contaminated fuel condition. Refer to Alcohol/Contaminants-in-Fuel Diagnosis (w/o Special Tool) or Alcohol/Contaminants-in-Fuel Diagnosis (w/Special Tool) . Verify that each injector harness is connected to the correct injector/cylinder according to the firing order. Test the fuel injectors. Refer to Fuel Injector Coil Test . Test the items that cause an engine to run rich. For a rich condition, refer to DTC P2178 or P2180 and DTC P2188 or P2190 . Test the items that can cause an engine to run lean. For a lean condition, refer to DTC P2177 or P2179 and DTC P2187 or P2189 . |
| Sensor/System | Test the throttle actuator control (TAC) system. Refer to DTC P0506 or P0507 . Test the crankcase ventilation system. Refer to Crankcase Ventilation System Inspection/Diagnosis in Engine Mechanical - 3.6L (LY7). Monitor the knock sensor (KS) system for excessive spark retard activity with a scan tool. Refer to Knock Sensor (KS) System Description , DTC P0327 or P0332 , and DTC P0328 or P0333 . |
| Ignition System | Inspect for the correct installation of the ignition coil seals. Incorrect installation may allow water to enter the spark plug area. Inspect for moisture and corrosion. Test for the correct ignition voltage output with a J 26792 Spark Tester. See Special Tools . If you suspect an ignition system condition, refer to Electronic Ignition (EI) System Diagnosis . Remove the spark plugs and inspect for the following conditions: Incorrect heat range Wet plugs Cracks Wear Improper gap Burned electrodes Heavy deposits Refer to the following procedures: Spark Plug Replacement Ignition System Specifications Spark Plug Inspection If the spark plugs are gas, coolant, or oil fouled, determine the cause before replacing the spark plugs. Refer to the following procedures: Test the items that cause an engine to run rich. For a rich condition, refer to DTC P2178 or P2180 and DTC P2188 or P2190 . For diagnosis of coolant contaminated spark plugs, refer to Loss of Coolant in Engine Cooling. For diagnosis of oil fouled spark plugs, refer to Oil Consumption Diagnosis in Engine Mechanical - 3.6L (LY7). Inspect the spark plug boots and terminals for burning or micro-arcing, corrosion, and damage to the insulation. Inspect the crankshaft position (CKP) sensor for the correct resistance. The sensor resistance may be out of range after a hot soak. Measure that the resistance remains within 700-1,200 ohms at all temperatures. |
| Engine Mechanical | Inspect for a condition with the camshaft actuator system. A camshaft actuator that is stuck in the full advance or retard position may cause this symptom. Refer to DTC P0011, P0014, P0021, or P0024 . Inspect for the following engine mechanical conditions: Excessive oil in combustion chamber or leaking valve seals Incorrect cylinder compression Sticking or leaking valves Worn camshaft lobes Camshaft timing Broken valve springs Excessive carbon buildup in the combustion chambers - Clean the chambers with top engine cleaner. Follow the instructions on the can. For more information, refer to the following procedures in Engine Mechanical - 3.6L (LY7): Oil Consumption Diagnosis Engine Compression Test Camshaft Timing Drive Chain Alignment Diagram (With Primary Roller Chain) or Camshaft Timing Drive Chain Alignment Diagram (W/Primary (IT) Inverted Tooth Chain) Setting Camshaft Timing Symptoms - Engine Mechanical Inspect the following components for incorrect basic engine parts: Camshafts Cylinder heads Pistons, connecting rods, or bearings. Refer to the following procedures in Engine Mechanical - 3.6L (LY7): Camshaft Timing Drive Components Cleaning and Inspection Camshaft Cleaning and Inspection Cylinder Head Cleaning and Inspection Piston, Connecting Rod, and Bearings Cleaning and Inspection |
| Additional | Inspect the vacuum hoses for splits and kinks. Verify that the connections and routing are as shown on the Vehicle Emission Control Information Label. Refer to Emission Hose Routing Diagram . Inspect for vacuum leaks in the following areas: The upper and lower intake manifolds The throttle body The positive crankcase ventilation (PCV) system The vacuum brake booster Inspect the evaporative emission (EVAP) canister purge solenoid for the following: A stuck open condition Charcoal contamination due to a defective EVAP canister For more information, refer to Evaporative Emission (EVAP) Control System Description . Inspect the following exhaust system components: The exhaust system components for damage The mufflers for heat distress or possible internal failure The three-way catalytic converters for restrictions For more information, refer to Symptoms - Engine Exhaust . Electromagnetic interference (EMI) on the CKP sensor signal circuits can cause an engine misfire condition. You can usually detect EMI with a scan tool by monitoring the engine speed parameter. A sudden increase in the engine speed parameter, with little change in actual engine speed indicates that EMI is present. Inspect for high voltage components near the ignition control circuits if a condition exists. Also, inspect the engine ground shield of the CKP sensor circuits. Inspect for a condition with the engine mounts. Refer to Engine Mount Replacement - Left or Engine Mount Replacement - Right (W/RWD) or Engine Mount Replacement - Right (W/AWD) in Engine Mechanical - 3.6L (LY7). |
Rough, Unstable, or Incorrect Idle and Stalling
Dieseling, Run-On
| Inspections | Action |
|---|---|
| DEFINITION: The engine continues to run after the key is turned OFF, but runs very rough. If the engine runs smooth, inspect the ignition switch and the ignition switch adjustment. | |
| Preliminary | Refer to Important Preliminary Checks Before Starting in Symptoms - Engine Controls . Search for bulletins. Verify that the engine control module (ECM) and ECM bracket fasteners are at the correct torque. Inspect the engine control system grounds for being clean, tight, and in the correct locations. Refer to Engine Controls Schematics . Ensure the resistance between the ECM housing and the battery negative cable is less than 0.5 ohms. |
| Fuel System | Test the fuel system for the following conditions: High fuel system pressure Leaking fuel injectors For more information, refer to Fuel System Diagnosis . |
Dieseling, Run-On
Backfire
| Inspections | Actions |
|---|---|
| DEFINITION: Fuel ignites in the intake manifold or in the exhaust system, making a loud popping noise. | |
| Preliminary | Refer to Important Preliminary Inspections Before Starting in Symptoms - Engine Controls . Search for bulletins. Inspect the engine control system grounds for being clean, tight, and in the correct locations. Refer to Engine Controls Schematics . Ensure the resistance between the engine control module (ECM) housing and the battery negative cable is less than 0.5 ohms. Verify that the ECM and ECM bracket fasteners are at the correct torque. |
| Fuel System | Test for incorrect fuel pressure. Refer to Fuel System Diagnosis . Test for a restricted fuel filter. Refer to Fuel System Diagnosis . Test for a contaminated fuel condition. Refer to Alcohol/Contaminants-in-Fuel Diagnosis (w/o Special Tool) or Alcohol/Contaminants-in-Fuel Diagnosis (w/Special Tool) . Inspect that each injector harness is connected to the correct injector/cylinder according to the firing order. Test the fuel injectors. Refer to Fuel Injector Coil Test . Test the items that can cause an engine to run lean. For a lean condition, refer to DTC P2177 or P2179 and DTC P2187 or P2189 . |
| Sensor/System | Inspect the air intake system and the crankcase for air leaks. Test the crankcase ventilation system for the correct operation. Refer to Crankcase Ventilation System Inspection/Diagnosis in Engine Mechanical - 3.6L (LY7). Monitor the knock sensor (KS) system for excessive spark retard activity with a scan tool. Refer to Knock Sensor (KS) System Description , DTC P0327 or P0332 , and DTC P0328 or P0333 . |
| Ignition System | Inspect for the correct installation of the ignition coil seals. Incorrect installation may allow water to enter the spark plug area. Inspect for moisture and corrosion. Test for the correct ignition voltage output with a J 26792 Spark Tester. See Special Tools . If you suspect an ignition system condition, refer to Electronic Ignition (EI) System Diagnosis . Remove the spark plugs and inspect for the following conditions: Incorrect heat range Wet plugs Cracks Wear Improper gap Burned electrodes Heavy deposits Refer to the following procedures: Spark Plug Replacement Ignition System Specifications Spark Plug Inspection If the spark plugs are gas, coolant, or oil fouled, determine the cause before replacing the spark plugs. Refer to the following procedures: Test the items that cause an engine to run rich. For a rich condition, refer to DTC P2178 or P2180 and DTC P2188 or P2190 . For diagnosis of coolant contaminated spark plugs, refer to Loss of Coolant in Engine Cooling. For diagnosis of oil fouled spark plugs, refer to Oil Consumption Diagnosis in Engine Mechanical - 3.6L (LY7). Inspect the spark plug boots and terminals for burning or micro-arcing, corrosion, and damage to the insulation. Inspect the crankshaft position (CKP) sensor for the correct resistance. The sensor resistance may be out of range after a hot soak. Measure that the resistance remains within 700-1,200 ohms at all temperatures. |
| Engine Cooling System | Inspect the engine coolant level for being low. Refer to Draining and Filling Cooling System in Engine Cooling. Inspect the engine thermostat for the correct operation and heat range. Refer to Thermostat Diagnosis in Engine Cooling. |
| Engine Mechanical | Inspect for the following engine mechanical conditions: Excessive oil in combustion chamber or leaking valve seals Incorrect cylinder compression Sticking or leaking valves Worn camshaft lobes Camshaft timing Broken valve springs Excessive carbon buildup in the combustion chambers - Clean the chambers with top engine cleaner. Follow the instructions on the can. For more information, refer to the following procedures in Engine Mechanical - 3.6L (LY7): Oil Consumption Diagnosis Engine Compression Test Camshaft Timing Drive Chain Alignment Diagram (With Primary Roller Chain) or Camshaft Timing Drive Chain Alignment Diagram (W/Primary (IT) Inverted Tooth Chain) Setting Camshaft Timing Symptoms - Engine Mechanical Inspect the following components for incorrect basic engine parts: Camshafts Cylinder heads Pistons, connecting rods, or bearings Refer to the following procedures in Engine Mechanical - 3.6L (LY7): Camshaft Timing Drive Components Cleaning and Inspection Camshaft Cleaning and Inspection Cylinder Head Cleaning and Inspection Piston, Connecting Rod, and Bearings Cleaning and Inspection |
| Additional | Inspect the vacuum hoses for splits and kinks. Verify that the connections and routing are as shown on Vehicle Emission Control Information. Refer to Emission Hose Routing Diagram . Inspect the intake manifold and the exhaust manifold passages for casting flash. Test the transmission torque converter clutch (TCC). The scan tool should indicate a drop in engine speed when the TCC is commanded ON. Refer to Torque Converter Diagnosis Procedure in Automatic Transmission - 5L40-E/5L50-E. Inspect the following exhaust system components: The exhaust system for damage The exhaust manifold for a collapsed inner wall The mufflers for heat distress or possible internal failure The three-way catalytic converters for restrictions For more information, refer to Symptoms - Engine Exhaust in Engine Exhaust. Electromagnetic interference (EMI) on the CKP sensor signal circuits can cause an engine misfire condition. You can usually detect EMI with a scan tool by monitoring the engine speed parameter. A sudden increase in the engine speed parameter, with little change in actual engine speed indicates that EMI is present. Inspect for high voltage components near the ignition control circuits if a condition exists. Also, inspect the engine ground shield of the CKP sensor circuits. Test the park neutral position (PNP) switch circuit. Refer to DTC P0850 in Automatic Transmission - 5L40-E/5L50-E. |
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 heated oxygen sensor (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 need every possible emission control system. 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; if equipped
- Air conditioning system refrigerant
- Catalytic converter efficiency
- Comprehensive component monitoring - Emission related inputs and outputs
- Evaporative emissions (EVAP) system
- Fuel delivery system
- Heated catalyst monitoring
- Misfire monitoring
- Oxygen sensor system (O2S or HO2S)
- Oxygen sensor heater system (HO2S Heater)
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.