Symptoms - Engine Controls
Diagnostic Instructions
Symptoms Description
Symptoms covers conditions that are not covered by DTCs. Certain conditions can cause multiple symptoms. These conditions are listed together under Symptoms Testing. Conditions that may only cause specific symptoms are listed separately under Additional Symptoms Testing. Perform the Symptoms Testing before using the Additional Symptoms Testing.
Symptoms Definition
Backfire: The fuel ignites in the intake manifold or in the exhaust system, making a loud popping noise.
Cuts Out, Misfires: 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.
Detonation/Spark Knock: A mild to severe ping which usually occurs worse while under acceleration. The engine makes sharp metallic knocks that change with throttle opening.
Dieseling, Run-On: The engine continues to run after the key is turned OFF, but runs very rough.
Engine Control Module (ECM) Commanded Reduced Engine Power: The ECM illuminates the Reduced Engine Power lamp and will limit engine power under potential engine/vehicle damaging or emissions related conditions. A DTC may not be set.
Fuel Odor: A noticeable smell of unburned fuel.
Hard Start: The engine cranks OK, but does not start for a long time. The vehicle does eventually run, or may start but immediately stall.
Hesitation, Sag, Stumble: A 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. This condition may cause the engine to stall in severe conditions.
Lack of Power, Sluggishness, or Sponginess: The engine delivers less than expected power. Little or no increase in vehicle speed when the accelerator pedal is pushed down part way.
Poor Fuel Economy: 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.
Poor Fuel Fill Quality: Difficulty when refuelling the vehicle.
Rough, Unstable, or Incorrect Idle and Stalling: The engine runs unevenly at idle. If severe, the engine or the vehicle may shake. Engine idle speed may vary. Either condition may be severe enough to stall the engine.
Surges/Chuggles: An engine power variation under steady throttle or cruise. Feels like the vehicle speeds up and slows down with no change in the accelerator pedal position.
Symptoms Verification
Before using the Symptom tables, perform the following:
| • | Verify that the malfunction indicator lamp (MIL) is operating correctly. Use the scan tool to command the lamp ON and OFF. |
| • | Verify that there are no DTCs that are stored. |
| • | Verify that the scan tool data is within a normal operating range. Refer to Control Module References for scan tool information. |
| • | Verify the customer concern. |
| • | Perform the Visual/Physical Inspection in this section. The visual/physical inspection is extremely important, and can lead to correcting a condition without additional testing. It may also help reveal the cause of an intermittent condition. |
Identifying Intermittent Conditions
Many intermittent conditions occur with harness or connector movement due to engine torque, rough pavement, vibration or physical movements of a component. Refer to the following for a list of issues that may cause an intermittent condition:
| • | Moisture and water intrusion in connectors, terminals, and components |
| • | Incomplete connector mating |
| • | High circuit or component resistance-High resistance can include any resistance, regardless of the amount, which can interrupt the operation of the component. |
| • | Harness that is too short or tight |
| • | Wire insulation that is chaffed or cut |
| • | High or low ambient temperature |
| • | High or low engine coolant temperatures |
| • | High underhood temperatures |
| • | Heat build up in component or circuit due to circuit resistance, poor terminal contact, or high electrical load |
| • | High or low system voltage |
| • | High vehicle load conditions |
| • | Electro-magnetic interference (EMI)/circuit interference from relays, solenoids or other electrical surge |
| • | Incorrect installation of aftermarket, add on accessories |
Visual/Physical Check
| • | Verify that the control module grounds are clean, tight, and correctly located. |
| • | Verify that the vacuum hoses are not split or kinked, and are properly connected, as shown on the Vehicle Emission Control Information label. |
| • | Verify that the air filter is clean and free from restrictions. |
| • | Verify that there is no water intrusion in connectors, terminals and components. |
| • | Inspect the air inlet ducts for the following conditions: |
| • | Inspect for air leaks at the throttle body mounting area, the mass air flow (MAF) sensor and inlet manifold sealing surfaces. |
| • | Inspect the wiring harness for the following conditions: |
| • | Inspect for loose, damaged, unseated, or missing sensors/components. |
| • | Inspect the terminals for corrosion and correct contact. |
Symptoms Testing
Backfire, Cuts Out/Misfires, Detonation/Spark Knock, Dieseling/Run-On, Hard Start, Hesitation/Sag/Stumble, Lack of Power/Sluggishness/Sponginess, Poor Fuel Economy, Rough, Unstable, or Incorrect Idle and Stalling, or Surges/Chuggles
| • | Test the fuel system for the following: |
| • | Test the ignition system for the following: |
| - | For diagnosis of coolant or oil fouled spark plugs--Refer to
Coolant in Combustion Chamber : LE5 or LE9 or Oil Consumption Diagnosis : LE5 or LE9 . |
| - | Wet down the secondary ignition system with water from a spray bottle--Wetting down the secondary ignition system may help locate damaged or deteriorated components. Look/listen for arcing or misfiring as the water is applied. |
| • | Inspect for the following conditions: |
| - | For vehicles equipped with automatic transmission, the proper operation of the transmission torque converter clutch (TCC)--The scan tool should indicate an engine speed drop when the TCC is commanded ON. Refer to Torque Converter Diagnosis . |
| - | Improper operation of the A/C compressor |
| - | An engine that runs lean or rich--Observe the Fuel Trim parameters with a scan tool and refer to DTC P0171 or P0172 . |
| - | Slow responding heated oxygen sensors (HO2S)--The HO2S should respond quickly to different throttle positions. |
Caution: Refer to Heated Oxygen and Oxygen Sensor Caution in the Preface section.
| - | Water intrusion in the HO2S connector |
| | Note: The embossed arrows on the mass air flow (MAF) sensor indicate the direction of the intake air flow. The arrows must point toward the engine. |
| - | Incorrect MAF sensor installation. A MAF sensor that is incorrectly installed may cause a hard start. Install the MAF in the correct direction. Refer to
Mass Airflow Sensor with Inlet Air Temperature Sensor Replacement : LE5 or LE9 . |
| - | Improper mass air flow (MAF) sensor connections. |
| - | Engine oil contaminated by fuel |
| - | Split or kinked vacuum hoses--Verify that the routing and connections are as shown on the Vehicle Emission Control Information label. |
| - | Knock sensor system excessive spark retard activity--Observe the Knock Retard parameter on the scan tool for activity more than 0°. For more information and component testing instructions, refer to
DTC P0325, P0326, P0327, or P0328 : LE5, LE9 . |
| • | Inspect the exhaust system components for the following: |
| - | Physical damage or possible internal failure |
| - | Restricted three-way catalytic converters |
| • | Electromagnetic interference (EMI) on the reference circuit can cause a 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 the high voltage components near the ignition control circuit if a condition exists. |
| • | Inspect the crankcase ventilation valve for proper operation--Refer to
Crankcase Ventilation System Inspection/Diagnosis : LE5 or LE9 . |
| • | Verify that the evaporative emission (EVAP) canister purge solenoid is not stuck open |
| • | Inspect the engine cooling system for the following conditions: |
| - | Improper engine coolant level--If the level is low, refer to Loss of Coolant . |
| • | Inspect the crankshaft position sensor for an intermittent condition--Observe the scan tool Crankshaft Position Resync Counter parameter. The parameter should remain at 0 during all operating conditions, and when moving the related harnesses and connectors between the crankshaft position sensor and the ECM. |
| • | Inspect the engine for the following mechanical failures: |
| | Refer to
Symptoms - Engine Mechanical : LE5 or LE9 . |
| - | Excessive oil in the combustion chamber or leaking valve seals |
| - | Incorrect cylinder compression |
| - | Sticking or leaking valves |
| - | Excessive carbon buildup in the combustion chambers--Clean the chambers with top engine cleaner. Follow the instructions on the can. |
| • | If the above conditions do not address the symptom, refer to the additional symptoms tests. |
Additional Symptoms Tests
Hard Start
| • | Observe the TB Idle Airflow Compensation parameter with a scan tool. A value greater than 80 % may indicate an excessive accumulation of deposits in the throttle bore. Inspect the throttle body and clean, if necessary. |
| • | Test the engine coolant temperature (ECT) sensor. Compare the ECT sensor value to the inlet 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 Versus Resistance for resistance specifications. Replace the ECT sensor if the resistance is not within specification. Refer to Engine Coolant Temperature Sensor Replacement : LE5 , LE9 or LAF . If the sensor is within the specification, test the ECT sensor circuits for high resistance. |
| • | Inspect for excessive crankshaft endplay that will cause the crankshaft position sensor reluctor wheel to move out of alignment with the crankshaft position sensor. Refer to
Crankshaft and Bearing Cleaning and Inspection : LE5 or LE9 . |
Hesitation, Sag, Stumble
| • | Inspect the mass air flow (MAF) sensor for obstruction, contamination, and damage. Refer to
Mass Airflow Sensor with Inlet Air Temperature Sensor Replacement : LE5 or LE9 . |
| • | Test the generator. Refer to Symptoms - Engine Electrical . Repair the charging system if the generator output voltage is less than 9 V or more than 16 V. |
| • | Inspect for excessive crankshaft endplay that will cause the crankshaft position sensor reluctor wheel to move out of alignment with the crankshaft position sensor. Refer to
Crankshaft and Bearing Cleaning and Inspection : LE5 or LE9 . |
| • | Test the manifold absolute pressure (MAP) sensor. Refer to DTC P0106 . |
| | Note: The following actions may need to be repeated in order to verify an intermittent intake or exhaust camshaft actuator condition. |
| • | Engine warm and idling, verify the correct operation of the camshaft actuator system. Command the intake and exhaust camshaft actuators from 0 degrees to 25 degrees and back to zero while observing the scan tool Int. CMP Variance and Exh. CMP Variance parameters. Each parameter should be less than 2 degrees in each of the commanded states. |
| ⇒ | If any of the parameters is greater than 2 degrees, inspect the suspect camshaft actuator and camshaft actuator solenoid valve and valve bore for contamination, obstruction, and damage. Refer to
Camshaft Position Actuator Solenoid Valve Replacement : LE5 or LE9 and Camshaft Actuator System Description . |
Poor Fuel Economy
| • | Heavy loads being carried or towed |
| • | Acceleration rate too much or too often |
| • | Inspect the brake system for brake drag. |
| • | Inspect for incorrect operation of the speedometer. |
| • | Verify that the engine coolant temperature (ECT) has not shifted in value. Allow the engine to run and reach operating temperature. Observe the ECT Sensor parameter with a scan tool and compare the reading to that parameter listed on the
Engine Control Module Scan Tool Information : LNQ → LE5 w/GDS → LF1 w/GDS list. If the reading is not in the range specified in the list, test the resistance of the ECT sensor. Refer to Temperature Versus Resistance for resistance specifications. Replace the ECT sensor if the resistance is not within specification. Refer to Engine Coolant Temperature Sensor Replacement : LE5 , LE9 or LAF . If the sensor is within the specification, test the ECT sensor circuits for high resistance. |
| • | Inspect the mass air flow (MAF) sensor for obstruction, contamination, and damage. Refer to
Mass Airflow Sensor with Inlet Air Temperature Sensor Replacement : LE5 or LE9 . |
| • | Observe the TB Idle Airflow Compensation parameter with a scan tool. A value greater than 80 % may indicate an excessive accumulation of deposits in the throttle bore. Inspect the throttle body and clean, if necessary. |
Detonation/Spark Knock
| • | Inspect for excessive carbon buildup in the combustion chambers. Clean the chambers with Top Engine Cleaner. Follow the instructions on the can. |
| • | Verify that the engine coolant temperature (ECT) has not shifted in value. Allow the engine to run and reach operating temperature. Observe the ECT Sensor parameter with a scan tool and compare the reading to that parameter listed on the
Engine Control Module Scan Tool Information : LNQ → LE5 w/GDS → LF1 w/GDS list. If the reading is not in the range specified in the list, test the resistance of the ECT sensor. Refer to Temperature Versus Resistance for resistance specifications. Replace the ECT sensor if the resistance is not within specification. Refer to Engine Coolant Temperature Sensor Replacement : LE5 , LE9 or LAF . If the sensor is within the specification, test the ECT sensor circuits for high resistance. |
| • | If there are no engine mechanical faults, fill the fuel tank with a known high quality fuel that meets the vehicle minimum octane requirements. |
Lack of Power, Hesitation, or Cut Out
| • | Verify that each injector harness is connected to the correct injector. |
| • | Inspect the mass air flow (MAF) sensor for obstruction, contamination, and damage. Refer to
Mass Airflow Sensor with Inlet Air Temperature Sensor Replacement : LE5 or LE9 . |
| | Note: The following actions may need to be repeated in order to verify an intermittent intake or exhaust camshaft actuator condition. |
| • | Engine warm and idling, verify the correct operation of the camshaft actuator system. Command the intake and exhaust camshaft actuators from 0 degrees to 25 degrees and back to zero while observing the scan tool Int. CMP Variance and Exh. CMP Variance parameters. Each parameter should be less than 2 degrees in each of the commanded states. |
| ⇒ | If any of the parameters is greater than 2 degrees, inspect the suspect camshaft actuator and camshaft actuator solenoid valve and valve bore for contamination, obstruction, and damage. Refer to
Camshaft Position Actuator Solenoid Valve Replacement : LE5 or LE9 and Camshaft Actuator System Description . |
Poor Fuel Fill Quality
Inspect for the following:
| • | The EVAP vent valve is stuck closed |
| • | A condition with the internal components of the fuel tank assembly--For more information, refer to Fuel System Description |
Rough, Unstable, or Incorrect Idle and Stalling
| • | Observe the TB Idle Airflow Compensation parameter with a scan tool. A value greater than 80 % may indicate an excessive accumulation of deposits in the throttle bore. Inspect the throttle body and clean, if necessary. |
| • | Inspect the mass air flow (MAF) sensor for obstruction, contamination, and damage. Refer to
Mass Airflow Sensor with Inlet Air Temperature Sensor Replacement : LE5 or LE9 . |
| • | Inspect the engine mounts. Refer to
Engine Mount Inspection : LE5 or LE9 . |
| • | Inspect the inlet and exhaust manifolds for casting flash. |
Surges/Chuggles
| • | Inspect the mass air flow (MAF) sensor for obstruction, contamination, and damage. Refer to
Mass Airflow Sensor with Inlet Air Temperature Sensor Replacement : LE5 or LE9 . |
| • | Test the heated oxygen sensors (HO2S). The HO2S should respond quickly to a change in throttle position. If the HO2S do not respond to different throttle positions, inspect for contamination from fuel, silicon, or the incorrect use of RTV sealant. The sensors may have a white powdery coating and result in a high, but false, signal voltage, which gives a rich exhaust indication. The PCM reduces the amount of fuel delivered to the engine, causing a driveability condition. |
| • | Verify that each injector harness is connected to the correct injector. |
Fuel Odour
| • | Inspect for damaged or deteriorated fuel lines. |
ECM Commanded Reduced Engine Power
Review the Reduced Engine Power History parameter with a scan tool to determine the reason for the last reduced engine power event.
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