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REDUCED ENGINE POWER. Every so often, four times the past 2-years, my 2007 G6 Pontiac (3.9 L V6, 33,000 miles) the reduced engine warning light comes on and the vehicle slows to about 5-10 mph. Needless to say this is a very dangerous situation in heavy traffic(especially Interstate) with 18-wheelers, other trucks, highway traffic, etc. it's almost impossible to get out of traffic. Upon resetting the computer, the vehicle runs fine until months later it happens again. Posts with other GM cars have this problem and no one seems to have a solution even after replacing throttle body, pedal sensor, wiring, steering wheel position sensor, engine control module, wheel speed sensor, etc., etc. Is anyone else experiencing this problem? Any real solution that works? Can the reduced engine power feature be disabled?
 

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reduced engine power

Thanks for the reply greenman. Looking at internet posts on the G6 and other vehicles, especially other GM cars, the codes lead to many different types of repairs, only to have the problem re-appear days, weeks or months later. I have yet to see a solution that works. It is a transient condition for most of us with this problem. The car goes into reduced engine power mode, then minutes later after turning power off, the car runs fine. In my case three-six months later it happens again. IT IS A VERY DANGEROUS SITUATION because if I were on the Interstate and it happened I wouldn't be able to get off the road in that traffic after rapidly slowing down to 5-10 mph.
 

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My 2006 3.5 GT doesn't have this issue, mind you I only have 60K miles. You might have a faulty PCM - power control module. This is different than the ECM - engine control module. Or, the wiring harness itself might be the cause.

I've had my Ford Taurus in for a some regular maintenance items over the years only to pick it up and find that some of the fuses weren't pushed in all the way, same with my cruise control module on two difference occasions. It took me a few looks under the hood to realize things weren't plugged back in properly.

As greenman mentioned, scan for codes. Even if the engine light isn't on codes are stored for up to 50 restarts.
 

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REDUCED ENGINE POWER. Every so often, four times the past 2-years, my 2007 G6 Pontiac (3.9 L V6, 33,000 miles) the reduced engine warning light comes on and the vehicle slows to about 5-10 mph. Needless to say this is a very dangerous situation in heavy traffic(especially Interstate) with 18-wheelers, other trucks, highway traffic, etc. it's almost impossible to get out of traffic. Upon resetting the computer, the vehicle runs fine until months later it happens again. Posts with other GM cars have this problem and no one seems to have a solution even after replacing throttle body, pedal sensor, wiring, steering wheel position sensor, engine control module, wheel speed sensor, etc., etc. Is anyone else experiencing this problem? Any real solution that works? Can the reduced engine power feature be disabled?
the "reduced engine power" warning message is produced by the throttle actuator control (TAC) system & no, it absolutely cannot be disabled (nor would you want it to be).

every time u "reset the computer" (i'm assuming here u are pulling a battery terminal) u erase the dtc (& it's accompanying freeze frame data) from the PCM memory & the TAC system behaves normally as it no longer "sees" any issue but u have not fixed anything permanently. u just erased the best & maybe only evidence for possibly diagnosing the problem.

there is no simple "real solution that works" since there are many possible reasons the TAC might produce that warning message. u've provided zero evidence thus far to offer any advice that would not be classified as throwing parts at it. that said, if u want to try throwing a new throttle body at it u might get lucky.

but due to the very low frequency of occurrence, this one could be a serious PITA to solve.
 

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Since someone may be searching for possible answers with reduced power this could be relevant to the problem. This was an intermittent problem along with other issues. It did take a long time to find the answer as the loss of voltage usually means an open circuit.

I had a similar problem with my son's 2009 GT with the 3.5L engine.

There was a fault with the APP circuit. The fault was a low voltage at the sensor. I do not recall the specific code. The ECM then puts the engine in limp mode with default computer settings controlling the engine. Acceleration is limited due to the missing sensor values. Traction control is deactivated along with any unnecessary functions.

There was a loss of the 5 Volt2 source from the ECM. This feeds the throttle control and the pedal position sensor. (On some vehicles it may power the crankshaft sensor.)

There are two sources of the 5 volts to the APP sensor. 5V1 and 5V2, if either are missing then the ECM puts the car in limp mode.

What I found was a broken wire inside the insulation for the harness from the ECM to the X108 plug (Pin K) near the left fender under the hood. The way the wiring harness is installed keeps too much stress on the individual wires and they can be damaged. The wires have been looped into a nearly 180 degree bend. This can give an intermittent fault if the circuit opens and then closes back up. At one time checking the continuity of this circuit it actually checked good. Moving the wiring harness and/or unplugging and plugging in the harness connector may open the circuit again. I repaired the broken wire to restore normal operation. Once the 5V2 is restored the ECM will clear the faults and allow normal engine operation.

The XT108 connector brings the power from the ECM to the APP components. It is necessary to have a code and a schematic to find the specific problem. Everyone should have an OBD2 scanner if you plan to attempt diagnosing problems on your car. The code can lead you to an area for detailed troubleshooting using a DVM to obtain voltages. Then the ohmmeter is used to very the continuity of the circuit components. These can be obtained for relatively low costs.

A copy of the schematic shows only two places using the 5V2 source. I also have attached a copy of the throttle body connector. If the 5V2 is missing then it needs to be traced back to X108. The connectors to the ECM are not likely to be a problem.

I hope that this may help some one who is looking at this circuit for limp mode or APP issues.

Copies of the X108 locations will be attached for this problem. The schematics for the Engine Control and APP circuits is also attached. The pin locations and circuit connections for X108 and the throttle body are included.
 

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