Part 2
Symptoms - Engine Controls (Continued)
Diagnostic Instructions
ECM Commanded Reduced Engine Power
Under certain conditions the engine control module (ECM) 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 (LCV or LUK) Scan Tool Testing and ProceduresEngine Control Module Scan Tool Information (LTG) Scan Tool Testing and Procedures 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 Cooling Fan 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 ECM 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.
* Reduced engine power 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.
* Turbocharger boost pressure out of range, if equipped. Refer to DTC P0234 or P0299 P0234.
* 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 9°C (16°F) of a each other.
* Fuel temperature out of range too high. Observe the scan tool Fuel Temperature Sensor parameter.
* If equipped with automatic transmission, an incorrect learned brake pedal position (BPP) sensor. Verify the following do not exist:
- An engine control module has been replaced
- A BPP sensor that has been replaced
- An incorrect BPP sensor alignment or installation
If any of the above occurred, one of the following procedures must be performed:
* If equipped with LTG engine, perform the Brake Pedal Position Sensor Learn 6T70 (M7W) - Automatic Transmission
* If equipped with LCV engine, perform the Brake Pedal Position Sensor Learn (With 2.5L LCV)
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 Throttle Body Idle Airflow Compensation parameter with a scan tool. A value greater than 90 % may indicate an excessive accumulation of deposits in the throttle bore. Inspect the throttle body and clean, if necessary. Refer to Throttle Body Cleaning Procedures.
* Test the engine coolant temperature (ECT) sensor. 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 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 - Engine Coolant Temperature Sensor Electrical Specifications for resistance specifications. Replace the engine coolant temperature sensor if the resistance is not within specification. Refer to Engine Coolant Temperature Sensor Replacement Engine Coolant Temperature Sensor Replacement. If the sensor is within the specification, 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 ON. Refer to Fuel System Description Fuel System Description and Fuel System Diagnosis Fuel System Diagnosis.
* 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 Crankshaft and Bearing Cleaning and Inspection and Engine Mechanical Specifications (LCV) Engine Mechanical SpecificationsEngine Mechanical Specifications (LTG) Engine Mechanical Specifications.
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 (LCV) Service and RepairMass Airflow Sensor with Intake Air Temperature Sensor Replacement (LTG) 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 Crankshaft and Bearing Cleaning and Inspection and Engine Mechanical Specifications (LCV) Engine Mechanical SpecificationsEngine Mechanical Specifications (LTG) Engine Mechanical Specifications.
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 Position Actuator Exhaust Solenoid Valve Replacement Camshaft Position Actuator Exhaust Solenoid Valve Replacement , Camshaft Position Actuator Intake Solenoid Valve Replacement Camshaft Position Actuator Intake Solenoid Valve Replacement , and Camshaft Actuator System Description Description and Operation.
Lack of Power, Sluggishness, or Sponginess (Except LTG)
* Inspect the engine electrical system for incorrect 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 (LCV) Service and RepairMass Airflow Sensor with Intake Air Temperature Sensor Replacement (LTG) 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 Position Actuator Exhaust Solenoid Valve Replacement Camshaft Position Actuator Exhaust Solenoid Valve Replacement , Camshaft Position Actuator Intake Solenoid Valve Replacement Camshaft Position Actuator Intake Solenoid Valve Replacement , and Camshaft Actuator System Description Description and Operation.
Lack of Power, Sluggishness, or Sponginess (LTG)
* Inspect the engine electrical system for incorrect 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 (LCV) Service and RepairMass Airflow Sensor with Intake Air Temperature Sensor Replacement (LTG) 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 Position Actuator Exhaust Solenoid Valve Replacement Camshaft Position Actuator Exhaust Solenoid Valve Replacement , Camshaft Position Actuator Intake Solenoid Valve Replacement Camshaft Position Actuator Intake Solenoid Valve Replacement , and Camshaft Actuator System Description Description and Operation.
* Verify the correct operation of the turbocharger system. Perform the following:
- Inspect the turbocharger moving components for looseness, binding, wear and damage.
- Verify that the turbocharger air inlet ducts and outlet ducts are tightly sealed and that the air passages are not obstructed. Engine running, use a solution of dish soap and water in a spray bottle to pinpoint any air leaks.
- Inspect the turbocharger system for external fluid leaks. Inspect the gaskets and sealing surfaces and look for cracks in the turbocharger components. Refer to Turbocharger Leaking Fluids Externally Turbocharger Leaking Fluids Externally and Turbocharger Smoke or Smell Turbocharger Smoke or Smell.
- Inspect for excessive turbocharger system noise. Refer to Turbocharger Noise Turbocharger Noise.
- Inspect for a loss of turbocharger pressure. Refer to Turbocharger Loss of Boost Pressure Turbocharger Loss of Boost Pressure.
- For additional information, refer to Turbocharger System Description Description and Operation and Turbocharger Cleaning and Inspection Turbocharger Cleaning and Inspection.
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 Throttle Body Idle Airflow Compensation parameter with a scan tool. A value greater than 90 % may indicate an excessive accumulation of deposits in the throttle bore. Inspect the throttle body 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 (LCV or LUK) Scan Tool Testing and ProceduresEngine Control Module Scan Tool Information (LTG) Scan Tool Testing and Procedures 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 - Engine Coolant Temperature Sensor Electrical Specifications for resistance specifications. Replace the engine coolant temperature sensor if the resistance is not within specification. Refer to Engine Coolant Temperature Sensor Replacement Engine Coolant Temperature Sensor Replacement. 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 (LCV) Service and RepairMass Airflow Sensor with Intake Air Temperature Sensor Replacement (LTG) Service and Repair.
* Inspect the brake system for brake drag.
Rough, Unstable, or Incorrect Idle and Stalling
* Observe the Throttle Body Idle Airflow Compensation parameter with a scan tool. A value greater than 90 % may indicate an excessive accumulation of deposits in the throttle bore. Inspect the throttle body 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 (LCV) Service and RepairMass Airflow Sensor with Intake Air Temperature Sensor Replacement (LTG) Service and Repair.
* Inspect the engine mounts. Refer to Engine Mount Inspection Testing and Inspection.
* Inspect the intake and exhaust manifolds for casting flash.
* An excessively high idle may be due to the floor mat interfering with the accelerator pedal. With this condition present, it may not be possible to shift the transmission into gear. Inspect the accelerator pedal for binding and verify that the floor mat is not interfering with the accelerator pedal movement.
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 (LCV) Service and RepairMass Airflow Sensor with Intake Air Temperature Sensor Replacement (LTG) Service and Repair.
* Inspect for slow responding 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. Refer to DTC P0133, P013A, P013B, P013E, P013F, P015A, P015B, P2270, or P2271 P0133 for more information.