Detonation/Spark Knock

• Test the engine for an overheating condition. Refer to Symptoms - Engine Cooling .
• 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 

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 cluster. If equipped with the driver information center feature, a reduced engine power message may be displayed as well. A DTC may not be set.

A repair may not be necessary. Observe the scan tool Reduced Engine Power History parameter or refer to K20 Engine Control Module: Scan Tool Information (LUV, LUW or LWE) 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. 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 coolant or oil to overheat-Refer to, Cooling Fan Description and Operation (Gas) and Cooling System Description and Operation (1.8L LUW and LWE) 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® feature, reduced engine power may be due to OnStar® remote command. Verify the vehicle is not in the OnStar® initiated Stolen Vehicle Slowdown mode. Refer to OnStar Stolen Vehicle Slowdown Active and Remote Vehicle Speed Limiting Description and Operation for additional information.
• High pressure fuel system condition-Refer to Fuel System Diagnosis  and Fuel System Description to verify high pressure fuel system operation.
• 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 for additional information.
• Fuel temperature out of range too high
• An incorrect learned brake pedal position (BPP) sensor-Verify the following actions have not occurred:
  • An engine control module (ECM) has been replaced.
  • A BPP sensor has been replaced.
  • A BPP sensor is misaligned or incorrectly installed.

    If any of the above actions have occurred, the Brake Pedal Position Sensor Learn procedure must be performed.