Q: 2006 Pontiac Grand Prix GT reduced engine power.

asked by on July 20, 2017

I have a 2006 Pontiac Grand Prix GT. It's got the 3.8L 3800 Series III supercharged engine. The car overheated because of a cracked elbow pipe, blew gaskets and quit completely. After two years, I have it running again (I didn't have the time to repair it). Car sat for two years with the engine in the garage and the body outside. Now that it's fixed, car still won't go past 3,500 RPM's when I floor it in park. Car gets to 45 MPH and shows "Reduced Engine Power" then dies completely. Car idols at 1500 RPM's instead of 500, and will "gas itself" when stopped and in Drive. It will rev itself up between 1500 and 1900 RPM's and misses and shakes noticibly. I plugged into a computer and it showed codes for supercharger bypass valve, wheel sensors and ignition plate. Everything is new on it from pistons and gaskets and coil packs and spark plugs. Heard it might be throttle body. Bypass valve was replaced as well. ABS light, traction control and check engine light are on. Any ideas? Automatic not manual

My car has 147000 miles.
My car has a manual transmission.

Hey there. The reduced power light typically indicates a fairly serious problem with the throttle system. When this light illuminates the vehicle will often go into a “safe mode”, which will severely limit the speed of the car and in some cases will render the vehicle un-drivable. It’s always best to have a professional mechanic complete a reduced power light inspection to isolate the source of your issue. In regards to the other warning lights, it appears that this Grand Prix has multiple issues going on, so you might want to have the mechanic download those specific codes and help you diagnose the root source of those as well. In many cases, the code that might indicate a part failure is actually caused by a bad sensor or electrical harness.

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