Codes P0411, P0128 and U0107, reduced engine power

Tiny
LEEANN ALESHIRE
  • MEMBER
  • 2008 PONTIAC GRAND PRIX
  • 5.3L
  • V6
  • 2WD
  • AUTOMATIC
  • 179,000 MILES
Got a "reduced engine power" code and no acceleration one day after driving, put in park and reverse and then drive again. This was all of a sudden (literally). I had been driving like normal on that day. Pulling out of a parking space I tried to accelerate and the gas pedal didn't give me any acceleration. I then noticed the reduced engine power notification on the screen. I luckily was able to cross the street to an auto part store. The OBD codes came up as: P0411, P0128 (third was a repeated code and U0107. By the time I got to the auto part store the gas pedal went all the way to the floor with no change in the sound of engine revving or idle. The weirdest thing is that a day or two later, my boyfriend was able to get it started and move then it cut out again. He has changed the thermostat, water pump (he noticed it was leaking/spitting a bit) and serpentine belt. A mechanic Budd advised to clean the throttle body (I'm not sure how clean it has to be) and tried changing out the pedal with one he got from a junk yard car. He currently is checking/changing out spark plugs/wires. The only other thing that we've been advised to do is to check the fuel pump so that's next.
Tuesday, January 25th, 2022 AT 7:33 PM

3 Replies

Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 110,055 POSTS
Hi,

There is a loss of communication between the throttle position sensor on the throttle body and the accelerator position sensor on the gas pedal. This is usually the result of a serial data circuit and not a faulty component.

Now, interestingly, this car came with either a 5.3L V8 or a 3.8L V6. You indicated a 5.3L V6. I need confirmation on the engine size. Two of the codes you provided are not relevant for the 5.3 V8.

If it is the V6, I provided the diagnostics for the breakdown in communication. Pic 1 shows the diagnostics, pic 2 shows the wiring schematic, pic 3 shows the pin orientation at the throttle actuator control module. That is where the testing will need to be done to identify what is happening. Pic 4 shows the TAC module.

Here is a link that you may find helpful:

https://www.2carpros.com/articles/how-to-check-wiring

Let me know if the engine is the V6 and if you have other questions.

Take care,

Joe

See pics below

PS: This has nothing to do with the fuel pump or spark plugs/wires.

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Tuesday, January 25th, 2022 AT 8:20 PM
Tiny
LEEANN ALESHIRE
  • MEMBER
  • 2 POSTS
Yes, my car is v6. Would this problem also cause it to work 1 day and then not the next? Also, would it cause it to not stay started? From reading other's responses, it looks like this could be a common problem with grand prix (?).
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Friday, January 28th, 2022 AT 7:43 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 110,055 POSTS
Hi,

If it is a connection issue or a part starting to fail, certainly it could be intermittent. As far as not staying started, that can be a result as well.

As far as a common problem, not so much. However, there were a lot of these vehicles sold, so it may appear more than others.

Have you been able to go through the diagnostics I sent? If you have questions, I'll try my best to help.

Let me know.

Take care,

Joe
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Friday, January 28th, 2022 AT 6:14 PM

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