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 (Without FX3) , K20 Engine Control Module: Scan Tool Information (FX3) , K20 Engine Control Module: Scan Tool Information (LEB) and K20 Engine Control Module: Scan Tool Information (LL0) 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 control module 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.
- 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 and pressure.
- 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 P0111-P0114 for additional information.
- Fuel temperature out of range too high.
- If equipped with manual transmission, reduced engine power caused by transmission oil temperature that is out of range too high. Allow the transmission and transmission oil to cool down.