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 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 ECM to reduce engine power. Refer to Cooling Fan Description and Operation and Cooling System Description and Operation to verify correct operation of the cooling fan.
• Reduced engine power due to OnStar® remote command. Verify the vehicle is not in the OnStar® initiated Stolen Vehicle Slowdown mode.
• 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. Verify correct operation of the Intake Air Temperature (IAT) sensor. Compare the scan tool Start-Up IAT parameter to the ambient temperature. Refer to DTC P0112, P0113 or P0114 for specifications and additional information.
• Fuel temperature out of range too high.
• If equipped with a manual transmission, reduced engine power may be due to overheated transmission oil. Allow the transmission oil to cool down. Refer to the Owners Manual for scheduled maintenance recommendations to determine if the transmission fluid is due to be serviced.
• If equipped with automatic transmission, an incorrect learned brake pedal position (BPP) sensor. Verify the following actions have not occurred:
  • An engine control module has been replaced
  • A BPP sensor that has been replaced
  • A BPP sensor is misaligned or incorrectly installed

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