Part 2
Symptoms - Engine Controls
Symptoms Testing
Backfire, Cuts Out/Misses, Detonation/Spark Knock, Dieseling/Run-On, Engine Control Module (ECM) Commanded Reduced Engine Power, 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:
- Correct operation and pressure-Refer to Fuel System Diagnosis Fuel System Diagnosis.
- Improperly operating fuel injectors-Refer to Fuel Injector Solenoid Coil Test Fuel Injector Solenoid Coil Test.
- Improper fuel quality condition-Refer to Alcohol/Contaminants-in-Fuel Diagnosis Testing and Inspection.
* Test the ignition system for the following:
- Spark plugs with incorrect heat range or an abnormal condition-Refer to Spark Plug Inspection Testing and Inspection and Ignition System Specifications [1][2]Specifications.
- Coolant or oil fouled spark plugs-For diagnosis, refer to Coolant in Combustion Chamber Coolant in Combustion Chamber or Oil Consumption Diagnosis Oil Consumption Diagnosis.
- Secondary ignition system susceptible to moisture. Engine running, wet down the secondary ignition system with water from a spray bottle to help locate damaged or deteriorated components. Look/listen for arcing or misfiring as the water is applied.
- Weak spark using the J 26792 Spark Tester-Refer to Electronic Ignition System Diagnosis Electronic Ignition (EI) System Diagnosis.
* Inspect for the following conditions:
- Improper operation of the transmission torque converter clutch (TCC) - The scan tool should indicate an engine speed drop when the TCC is commanded ON. For Non-Hybrid equipped vehicles, refer to Torque Converter Diagnosis 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. Refer to DTC P0171 or P0172 P0171.
- Slow responding heated oxygen sensors (HO2S). The heated oxygen sensors should respond quickly to different throttle positions. Refer to DTC P0133, P0134, P013A, P013B, P013E, P013F, P0140, P1133, P2270, P2271, or P2A00 P0133 for additional information.
Caution: Refer to Heated Oxygen and Oxygen Sensor Caution Heated Oxygen and Oxygen Sensor Caution.
- Water intrusion in the heated oxygen sensors 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.
- Improper MAF sensor installation. A mass air flow sensor that is improperly installed may cause a hard start. Install the mass air flow in the proper direction. Refer to Mass Airflow Sensor with Intake Air Temperature Sensor Replacement Service and Repair.
- 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.
- Excessive knock sensor system spark retard activity-Observe the Knock Retard parameter on the scan tool for activity more than 0°.
* Electromagnetic interference (EMI) on the reference circuit, which can cause a misfire condition. You can usually detect electromagnetic interference 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 electromagnetic interference is present. Inspect the high voltage components near the ignition control circuit if a condition exists.
* A crankshaft position sensor with an intermittent condition-Observe the scan tool Crankshaft Position Resync Counter parameter. The Resync Counter 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.
* A stuck open evaporative emission (EVAP) canister purge solenoid.
* Improper operation of the crankcase ventilation valve-Refer to Crankcase Ventilation System Inspection/Diagnosis (Without Turbocharger) Testing and Inspection.
* The exhaust system components for the following:
- Physical damage or possible internal failure
- Restricted three-way catalytic converters
For more information, refer to Symptoms - Engine Exhaust Symptoms - Engine Exhaust.
* The engine cooling system for the following conditions:
- A thermostat with incorrect heat range. Refer to Thermostat Diagnosis Thermostat Diagnosis.
- Improper engine coolant level-If the level is low, refer to Loss of Coolant Loss of Coolant.
* Inspect the engine for the following mechanical failures:
Refer to Symptoms - Engine Mechanical Symptoms - Engine Mechanical.
- Excessive oil in the combustion chamber or leaking valve seals
- Oil Consumption
- Incorrect cylinder compression
- Sticking or leaking valves
- Worn camshaft lobes
- Incorrect valve timing
- Worn rocker arms
- Broken valve springs
- Excessive carbon buildup in the combustion chambers-Clean the chambers with top engine cleaner. Follow the instructions on the can.
- Incorrect engine parts
* If the above conditions do not address the symptom, refer to the additional symptoms tests.
Additional Symptoms Tests
Detonation/Spark Knock
* 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 (LUK) Engine Control Module Scan Tool Information (LUK)Engine Control Module Scan Tool Information (LEA) Engine Control Module Scan Tool Information (LEA) list. If the reading is not in the range specified in the list, test the resistance of the engine coolant temperature sensor. Refer to Temperature Versus Resistance Temperature Versus Resistance for resistance specifications. Replace the engine coolant temperature sensor if the resistance is not within specification. Refer to Engine Coolant Temperature Sensor Replacement Service and Repair. If the sensor is within the specification, test the engine coolant temperature sensor circuits for high resistance.
* Test for an engine overheating condition. Refer to Engine Overheating Engine Overheating.
* Inspect for excessive carbon buildup in the combustion chambers. Clean the chambers with Top Engine Cleaner, if necessary. Follow the instructions on the can.
* If there are no engine mechanical faults, fill the fuel tank with a known high quality fuel that meets the vehicle minimum octane requirements.
Engine Control Module (ECM) Commanded Reduced Engine Power (LUK)
Under certain conditions the engine control module may limit engine power by reducing engine torque and, for some vehicles, fuel pressure as well. For most, but not all of the conditions, the engine control module will illuminate the reduced engine power lamp on the instrument panel cluster, however a DTC may not be set. Observe the scan tool Reduced Engine Power History parameter, if applicable, or refer to Engine Control Module Scan Tool Information (LUK) Engine Control Module Scan Tool Information (LUK)Engine Control Module Scan Tool Information (LEA) Engine Control Module Scan Tool Information (LEA) to determine the reason for the reduced engine power event.
Verify or inspect for the following:
* Vehicle being operated at sustained high engine speeds, or, towing heavy loads up an incline for an extended period of time, which may cause the engine oil or coolant to overheat. A repair may not be necessary. Inspect the airflow passageways in front of the engine for obstructions and clear away any debris or foreign material that is found. If no obstructions are found, review approved driving habits with the customer. The customer may need to operate the vehicle at a higher engine speed to improve cooling system performance, or, at a slower engine speed to reduce engine load.
* A cooling fan condition which may cause the engine control module to reduce engine power. Refer to Cooling Fan Description and Operation (LAF , LEA, LUK) Cooling Fan Description and OperationCooling Fan Description and Operation (LDK or LHU) Cooling Fan Description and Operation and Cooling System Description and Operation Cooling System to verify correct operation of the cooling fan.
* Temporarily reduced engine power. Under extremely cold ambient temperatures some SIDI equipped vehicles may experience engine control module commanded reduced engine power for a few minutes during engine warm-up. This would be a normal condition, noticeable only at wide open throttle, and the reduced engine power lamp would not be illuminated.
* If the vehicle is equipped with the OnStar(R) feature, reduced engine power may be due to OnStar(R) remote command. Verify the vehicle is not in the OnStar(R) initiated Stolen Vehicle Slowdown mode. Refer to OnStar Stolen Vehicle Slowdown Active OnStar Stolen Vehicle Slowdown Active and Remote Vehicle Speed Limiting Description and Operation Remote Vehicle Speed Limiting for additional information.
* Excessively high fuel pressure condition. Refer to Fuel System Diagnosis Fuel System Diagnosis and Fuel System Description Fuel System Description to verify fuel system operation.
* Maximum recommended engine oil life exceeded. Refer to the Owners Manual for scheduled maintenance recommendations.
* Intake air temperature out of range too high. Engine running, observe the scan tool IAT Sensor parameter. The readings should be between -40°C and +149°C (-40°F and +300°F). Refer to DTC P0112, P0113, or P0114 (With LUK) Powertrain Management (With LUK)DTC P0112, P0113, or P0114 (With LEA) Powertrain Management (With LEA) for additional information.
* Fuel temperature out of range too high.
Engine Control Module (ECM) Commanded Reduced Engine Power (LAF or LEA)
Under certain conditions the engine control module may limit engine power by reducing engine torque and, for some vehicles, fuel pressure as well. For most, but not all of the conditions, the engine control module will illuminate the reduced engine power lamp on the instrument panel cluster, however a DTC may not be set. Observe the scan tool Reduced Engine Power History parameter, if applicable, or refer to Engine Control Module Scan Tool Information (LUK) Engine Control Module Scan Tool Information (LUK)Engine Control Module Scan Tool Information (LEA) Engine Control Module Scan Tool Information (LEA) to determine the reason for the reduced engine power event.
Verify or inspect for the following:
* Vehicle being operated at sustained high engine speeds, or, towing heavy loads up an incline for an extended period of time, which may cause the engine oil or coolant to overheat. A repair may not be necessary. Inspect the airflow passageways in front of the engine for obstructions and clear away any debris or foreign material that is found. If no obstructions are found, review approved driving habits with the customer. The customer may need to operate the vehicle at a higher engine speed to improve cooling system performance, or, at a slower engine speed to reduce engine load.
* A cooling fan condition which may cause the engine control module to reduce engine power. Refer to Cooling Fan Description and Operation (LAF , LEA, LUK) Cooling Fan Description and OperationCooling Fan Description and Operation (LDK or LHU) Cooling Fan Description and Operation and Cooling System Description and Operation Cooling System to verify correct operation of the cooling fan.
* Temporarily reduced engine power. Under extremely cold ambient temperatures some SIDI equipped vehicles may experience engine control module commanded reduced engine power for a few minutes during engine warm-up. This would be a normal condition, noticeable only at wide open throttle, and the reduced engine power lamp would not be illuminated.
* If the vehicle is equipped with the OnStar(R) feature, reduced engine power may be due to OnStar(R) remote command. Verify the vehicle is not in the OnStar(R) initiated Stolen Vehicle Slowdown mode. Refer to OnStar Stolen Vehicle Slowdown Active OnStar Stolen Vehicle Slowdown Active and Remote Vehicle Speed Limiting Description and Operation Remote Vehicle Speed Limiting for additional information.
* Excessively high fuel pressure condition. Refer to Fuel System Diagnosis Fuel System Diagnosis and Fuel System Description Fuel System Description to verify fuel system operation.
* Maximum recommended engine oil life exceeded. Refer to the Owners Manual for scheduled maintenance recommendations.
* Intake air temperature out of range too high. Observe the scan tool IAT Sensor 1 and IAT Sensor 2 parameters. The readings should be within 30°C (54°F) of a each other. Refer to DTC P2199 P2199 for additional information.
* Fuel temperature out of range too high.
Fuel Odor
* Inspect for leaking, damaged, or deteriorated fuel lines.
* Inspect for a saturated EVAP canister-Refer to Evaporative Emission Control System Description Description and Operation.
* Inspect for a condition with the internal components of the fuel tank assembly-Refer to Fuel System Description Fuel System Description.
Hard Start
* Observe the scan tool Throttle Body Idle Airflow Compensation parameter. A value greater than 80% may indicate an excessive accumulation of deposits in the throttle bore. Inspect the throttle body and bore and clean, if necessary. Refer to Throttle Body Cleaning Procedures.
* Test the engine coolant temperature (ECT) sensor. Compare the scan tool 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 engine coolant temperature sensor is out of range with the intake air temperature sensor, test the resistance of the engine coolant temperature sensor. Refer to Temperature Versus Resistance Temperature Versus Resistance for resistance specifications. Replace the engine coolant temperature sensor if the resistance is not within specification. Refer to Engine Coolant Temperature Sensor Replacement Service and Repair. If the sensor is within the specifications, test the engine coolant temperature sensor circuits for high resistance.
* Verify that the fuel system has adequate pressure for engine start-up. The fuel pump control module should command the fuel pump ON for 2 S when the ignition is turned to ON. Refer to Fuel System Description Fuel System Description and Fuel System Diagnosis Fuel System Diagnosis for correct fuel pressure specifications.
* 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 24. Crankshaft and Bearing Cleaning and Inspection.
Hesitation, Sag, Stumble
* Test the fuel pressure. Refer to Fuel System Diagnosis Fuel System Diagnosis.
* Inspect the mass air flow (MAF) sensor for obstruction, contamination, and damage. Refer to Mass Airflow Sensor with Intake Air Temperature Sensor Replacement Service and Repair.
* Test the generator. Refer to Symptoms - Engine Electrical Symptoms - Engine Electrical. Repair the charging system if the generator output voltage is less than 9 V or more than 16 V.
* Test the manifold absolute pressure (MAP) sensor. Refer to DTC P0106 P0106.
* 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 24. Crankshaft and Bearing Cleaning and Inspection.
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 Intake Camshaft Position Variance and Exhaust Camshaft Position 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 Actuator System Description Description and Operation , Camshaft Position Exhaust Actuator Replacement Camshaft Position Exhaust Actuator Replacement , and Camshaft Position Intake Actuator Replacement Camshaft Position Intake Actuator Replacement.
Lack of Power, Sluggishness, or Sponginess
* Inspect the engine electrical system for correct operation. Refer to Symptoms - Engine Electrical Symptoms - Engine Electrical.
* 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 Intake Air Temperature Sensor Replacement Service and Repair.
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 Intake Camshaft Position Variance and Exhaust Camshaft Position 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 Actuator System Description Description and Operation , Camshaft Position Exhaust Actuator Replacement Camshaft Position Exhaust Actuator Replacement , and Camshaft Position Intake Actuator Replacement Camshaft Position Intake Actuator Replacement.
Poor Fuel Economy
* Inspect for heavy loads being carried or towed
* Inspect for acceleration rate too much or too often
* Inspect for incorrect operation of the speedometer.
* Observe the scan tool Throttle Body Idle Airflow Compensation parameter. A value greater than 80% may indicate an excessive accumulation of deposits in the throttle bore. Inspect the throttle body and bore and clean, if necessary. Refer to Throttle Body Cleaning Procedures.
* 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 (LUK) Engine Control Module Scan Tool Information (LUK)Engine Control Module Scan Tool Information (LEA) Engine Control Module Scan Tool Information (LEA) list. If the reading is not in the range specified in the list, test the resistance of the engine coolant temperature sensor. Refer to Temperature Versus Resistance Temperature Versus Resistance for resistance specifications. Replace the engine coolant temperature sensor if the resistance is not within specification. Refer to Engine Coolant Temperature Sensor Replacement Service and Repair. If the sensor is within the specification, test the engine coolant temperature sensor circuits for high resistance.
* Inspect the mass air flow (MAF) sensor for obstruction, contamination, and damage. Refer to Mass Airflow Sensor with Intake Air Temperature Sensor Replacement Service and Repair.
* Inspect the brake system for brake drag.
Rough, Unstable, or Incorrect Idle and Stalling
* Observe the scan tool Throttle Body Idle Airflow Compensation parameter. A value greater than 80% may indicate an excessive accumulation of deposits in the throttle bore. Inspect the throttle body and bore and clean, if necessary. Refer to Throttle Body Cleaning Procedures.
* Inspect the mass air flow (MAF) sensor for obstruction, contamination, and damage. Refer to Mass Airflow Sensor with Intake Air Temperature Sensor Replacement Service and Repair.
* Inspect the engine mounts. Refer to Engine Mount Inspection Testing and Inspection.
* Inspect the intake and exhaust manifolds for casting flash.
Surges/Chuggles
* 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 Intake Air Temperature Sensor Replacement Service and Repair.
* Inspect for slow responding heated oxygen sensors (HO2S). The heated oxygen sensors should respond quickly to a change in throttle position. If the heated oxygen sensors 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 engine control module reduces the amount of fuel delivered to the engine, causing a driveability condition. Refer to DTC P0133, P0134, P013A, P013B, P013E, P013F, P0140, P1133, P2270, P2271, or P2A00 P0133 for additional information.