GM “Engine Power Reduced” Warning Message

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Many late model GM-made vehicles use an “Engine Power Reduced” mode when they detect a potentially catastrophic problem. Reduced engine power has been known to come on at very inopportune times (such as while driving on the highway).

Many components can cause the engine power to be reduced. The most common causes are usually an issue with the TAC system or the Throttle Position Sensor.

GM engine power reduced

What Does Engine Power Reduced Mean?

The Powertrain Control Module (PCM) has reduced the available engine power due to a system failure. Depending on the model and year of the vehicle in question, as well as what system actually failed, here’s what the Engine Power Reduced mode can do:

  • Throttle response will be limited
  • The fuel pump will shut off, and the vehicle won’t run at all
  • Transmission shift patterns can change
  • No throttle response

The owner’s manual that came with your specific vehicle will detail exactly how your car or truck will behave with the engine power reduced.

“Engine Power Reduced” Message: Diagnosis Strategy

Reduced Engine Power Diagnosis

There are many potential reasons why the Engine Power Reduced message can come on. Here’s how to narrow down what is wrong.

Pull the Diagnostic Codes

Use a scanner to pull up the diagnostic codes stored in the PCM. As you’ll see below, there are a lot of potential causes that can put a vehicle into the Engine Power Reduced mode.

Once you pull the code(s), you’ll want to focus on what causes that specific code, as “Engine Power Reduced” will be a symptom of that code.

Technical Service Bulletins

You can head over to the NHTSA website (it’ll open in a new tab) and look up the TSBs yourself. You can put in your make and model or use a VIN search. Once you do, you’ll want to click on manufacturer communications. That’s the TSB section.

You might get lucky and find a TSB that outlines a common reason why the Engine Power Reduced mode has come on, as well as a detailed repair guide. Finding the right TSB may take some digging, but it’ll be worth it in the amount of work you save yourself.

You should cross-reference the TSB with the codes you pulled with your scanner. If TSB and pulled code(s) seem to agree on the problem, following the TSB’s repair instructions would be your best course of action.

Once you put in your VIN or Make/Model, this is where you’ll find the TSBs

Reduced Engine Power Causes

As stated above, following the codes is the best way to fix the Engine Power Reduced warning. But, here are some of the most common reasons the code comes on.

  • Throttle Actuator Control (TAC)– The TAC module and control motor work together to open the throttle on drive-by-wire (computer-controlled) systems. When the signal from this system is not what it’s supposed to be, the PCM will reduce (or eliminate) the engine power.
  • Throttle/Peddle Position Sensor– The pedal position sensor tells the PCM how far down you’ve pushed the throttle. If it’s getting an unreliable signal from one of its circuits, reduced engine power will turn on.
  • Idle Position Not Learned– This’ll usually be accompanied by P2176.
  • MAP Sensor Issues– The Manifold Absolute Pressure (MAP) sensor calculates the density of the air entering the engine. Without an accurate reading, the engine power may be reduced.
  • Dirty Throttle Body– A dirty throttle body is known to cause reduced engine power. Often, when the throttle body is dirty, the engine will have a hard time finding the proper idle speed after the vehicle slows down. There will be a temporary drop in RPM below the normal idle speed before the PCM compensates for it.

Conclusion

Engine Power Reduced is GM’s way of keeping your vehicle safe when vital systems are no longer performing reliably. It can be a challenge to repair. Follow the codes and TSBs.