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 (LUZ) 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 (Diesel) and Cooling System Description and Operation (2.0L Diesel LUZ) to verify correct operation of the cooling fan.
• Fuel temperature out of range too high.
• High pressure fuel system out of range. Refer to Fuel System Diagnosis  and Fuel System Description to verify high pressure fuel system pressure and operation.
• Maximum recommended engine oil life exceeded. Refer to the Owners manual for scheduled maintenance recommendations.
• Reduced engine power due to OnStar® remote command. A repair may not be necessary. 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 or P0113 for additional information.
• Turbocharger boost pressure out of range. Refer to DTC P0234 or P0299 and Turbocharger System Description
• An incorrectly operating diesel exhaust reductant system. Refer to Exhaust Aftertreatment System Description and inspect for the following:
  • Incorrect exhaust fluid level
  • Contaminated or poor quality exhaust fluid
  • Reductant system malfunction
  • Reductant system that has been tampered with
• If equipped with manual transmission, excessively hot manual transmission fluid. Under severe operating conditions the fluid may become overheated, which may result in ECM commanded reduced engine power. Allow the transmission and fluid to cool down. Review the maintenance recommendation in the owners manual 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.