2004 Hummer H2
137000 miles

It all started with the throttle surging up and down when tach at approx 1500 rpm. That problem lasted at least 2 months before the code was thrown....the dreaded P1125 powertrain code.
Now the code itself says that the DBW (drive by wire) throttle circuit voltage is out of range for one of the sensors in that curcuit, Accelerator pedal sensor, throttle position sensor.

First things i tried were:
Replaced Accelerator pedal sensor (Oreilly's) -Nothing changed.
Decided the next logical step would be to replace the throttle position sensor on the throttle body, and my options are replacing the sensor only or the entire throttle body with sensor....i chose to just replace the entire throttle body.
After replacing with new throttle body i talked with the dealership and had to go through a re-learn process for the new sensor and throttle body.....did it!

The new throttle body had shown a instant improvement in throttle surge or lack there of, now when rpm's hit the 1500 mark instead of the normal surge it was a minor or very small flicker in throttle and on i went.
So here i am thinking i'm all good and fixed BOOM it goes into reduced engine mode on the freeway and nearly kills me trying to get out of the far left lane with no power at all. The next week i had the code thrown at least 5 times and can't go anywhere or rely on the truck so i felt i had to take to the dealer for a diagnostic.

So the dealer says after a full diagnostic and a rare support call to GM they have said that everything checks out normal including my ground connections and they couldn't get the code to throw while in their care that it all points to a intermittent open or short somewhere in the engine wire harness. The only option according to the dealer at this point is to replace the engine wire harness and they cannot go any farther until this is completed, so call me crazy or just stupid but i went ahead and purchase this special order harness at the low price of $1400 and waited a few days until it arrived then we had it installed by the dealer for another $1600.
They assured me that although they had not ever done a Hummer H2 engine harness before that they have done multiple silverado's with the same problem and changing this engine wiring solves the problem.

So 3 days after the new engine wiring harness it broke down again with the same code.... i have been all over the internet looking for others with this same problem and others are just as screwed as me as its pretty common in the GM vehicle world and i just assume that all the info out there are people like me in the troubleshooting process and that nobody is posting what infact they had to do to fix the problem....

Any help would be appreciated.

 

On your year of hummer its most likely the tac module. Throttle actuator control module. Its the module between the throttle pedal and throttle body that interprets pedal signals then sends signals to throttle body. If memory serves correct its mounted at left side of firewall just under left corner brace. Replaced several for this condition. Cant believe a gm dealer didn't know this as trucks of same vintage use same module.

 

I read about this module as well and it sounds logical to be the problem but i figured that the dealer said it should be fine i took to the internet.
Where would you buy this part?

 

Update....
I ordered this part: https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

will update as soon as i get her put in.

 

I also work at a dealer, so any ive replaced were from gm. Last thing I would ever sell a customer is a complete harness for this concern. Makes no sense to me why they did that. I would build a new harness from tac module to throttle body which is only 8 wires but not an entire engine harness.

 

CONTROL MODULE | Genuine GM | 12588923

 

I only went to this dealer because one of my neighbors had experience with them and said they are the best techs around.....hhhmmmm.

I really wish i would have hit this forum up before trusting the dealer but i just assumed they knew what they are doing. I appreciate your advice and ill let you know what happens.

 

I installed the TAC module on Friday and have noticed an instant change in how Harry drives, no hesitation no weird power fluctuations while on the highway.....Im not going to say it but its looking good.
Will update again in another week, that should be the true test.

 

UPDATE!!
Broke down today! I got the same code P1125 code.
So its not the TAC module, its not the throttle position sensor, its not the accelerator pedal sensor and its not the powertrain wiring........so what the hell could it be?? is it possible i put in a bad sensor?

Also it has happened when i pulled out of my driveway and the engine was still warming and not up to running temp.....not sure if this helps.

 

well if engine harness is new, tac module is new, throttle body is new and pedal assembly is new the only thing left is the wiring from throttle pedal to tac module. I would focus there