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Reduced Engine Power Message, surging idle

Diagnose Reduced Engine Power Message, surging idle

GM has issued a service bulletin PIP4578A to address a Reduced Engine Power Message, surging idle along with various trouble codes on the vehicles listed below.

Reduced engine power message and associated trouble codes

P0068 Throttle Body Airflow Performance
P0121 Throttle Position (TP) Sensor 1 Performance
P0506 Idle Speed Low
P0507 Idle Speed High
P1516 Throttle Actuator Control (TAC) Module Throttle Actuator Position Performance
P2101 Throttle Actuator Position Performance
P2119 Throttle Closed Position Performance
P2176 Minimum Throttle Position Not Learned

Vehicles affected

2007-2009 Cadillac CTS-V, Escalade
2008-2009 Chevrolet Colorado
2006-2009 Chevrolet Avalanche, Corvette, Express, Impala, Monte Carlo, Silverado,
Suburban, Tahoe, Trail Blazer
2008-2009 GMC Canyon
2006-2009 GMC Envoy, Savana, Sierra, Yukon
2007-2008 Hummer H2
2008-2009 Hummer H3
2007-2008 Pontiac Grand Prix
2008-2009 Pontiac G8
2006-2009 Saab 97x

With a V8 Engine

What causes Reduced Engine Power Message, surging idle

Over time, carbon builds up on the electronic throttle body. The ECM/PCM learns to compensate for the buildup by increasing the throttle plate angle to ensure the correct amount of air still enters the engine. However, if the carbon buildup exceeds a certain amount, the vehicle can develop an idle surge, hesitation on acceleration, a deceleration surge and overall reduced engine power. This is caused by a restricted air intake due to carbon buildup that the ECM/PCM can no longer override by adjusting throttle plate angle.

To respond, the ECM/PCM may set any of the trouble codes listed above and force the engine into reduced power mode while illuminating the reduced engine power message on the driver’s information center screen

How to fix reduced engine power message, surging idle

Examining the throttle body is the first step in addressing the reduced engine power mode issue. If you discover carbon buildup, it must be removed using the proper procedure and a throttle body relearn or “idle learn reset/reset idle learn” procedure must be performed afterward.

Clean the throttle body

See this post for instructions on how to clean the throttle body and perform an idle relearn procedure.

Clear the trouble codes

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Posted on by Rick Muscoplat

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