Engine Control Module (ECM) Commanded Reduced Engine Power

Under certain conditions the 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 ECM will illuminate the reduced engine power lamp on the instrument panel cluster, however 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 driven inappropriately. Towing heavy loads up an incline for an extended period of time or operating the vehicle at sustained, excessively high engine speeds 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 or conditions 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.
• Temporary 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.
• Fuel temperature out of range too high.
• High pressure fuel system condition. Refer to Fuel System Diagnosis  and Fuel System Description to verify high pressure fuel system pressure and operation.
• Reduced engine power 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.
• 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.
• 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.