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Greetings Eric the Car Guy forum!
I did a search but couldn’t find the answer to my question on this.
2008 Pontiac Grand Prix, base, 3.8 l 356,000 kms that’s 221,000 miles for you crazy Trumpidites down south!
Was driving a few days ago and after coming off the hiway after driving for about an hour the car jolts and then REDUCED ENGINE POWER displays on the dash. Car goes sluggish, low power, yadda, yadda, yadda. I know what this mode is for.
So I parked the car and let it cool down for the afternoon while I was at the beach and went back 4 hours later and drove it home. No issues on the way home but I took it really easy.
When I got home I hooked up my scanner and found it throwing P1125 (accelerator pedal sensor fault) and P2138 (Throttle/Pedal Pos Sensor/Switch D / E Voltage Correlation).
First thought was I just had the starter replaced at a shop (about 15,000 kms ago). Maybe they cut a wire or forgot a ground? So I inspected the wiring all around the top of the engine to the throttle body and such. And underneath the car where the starter is. A lot of the bailing around the wires was disintegrating (the car is old afterall) but the wires were not worn through or frayed.
The last 2 repairs were rear brakes and then front brakes. I don’t think this could have caused this??
So I moved onto the throttle body. I took the air filter out and replaced with new. The old one was 2 years old. I cleaned the MAF sensor (with the correct cleaner and I did not touch the sensor). Figured I would do this while I had everything apart. Took the boot off the throttle body and wow was it ever dirty.
I took the throttle body off the intake manifold and cleaned it. (using the correct type of throttle body cleaner and soft plastic brush and cotton cloth, when I was done it looked like new). When I took it apart,originally, I noticed that the carbon had made a ridge on the inside of the throttle body. I was thinking that maybe that ridge of carbon was stopping the butterfly valve from closing all the way. And the sensor was not aligning with the accelerator sensor causing the fault?? The car had been hard to start without hitting the throttle while turning it over. Once I cleaned everything and put it back together the car started much better and idled like it was new. Initial acceleration was also better.
Since I disconnected the negative terminal on the battery while I did the repair the error code was cleared when I restarted the car.
Today I drove the car to work. It ran better than it has in months. On my way home from work, this was after running the car for about 45 minutes, the car jolted and REDUCED ENGINE POWER came up on the display again.
Got home and I just hooked up the scanner and it reads P1125 and P2138. And also P1516 (Throttle Actuator Control Module Throttle Actuator Position Performance) and U0107 (Lost Communication With Throttle Actuator Control Module)
My question is how do I isolate what part is the problem here? I forgot to mention that I did run the car while wiggling the connector to the throttle body control and it did not go into RPM. I suspect the accelerator position sensor or the throttle position sensor.
I’m pretty sure it’s the throttle position sensor. I just want to make a proper diagnosis before I buy the part.
Thanks so much!
Stay dirty!
b
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do you have any freeze fram data??? might help to check that out and see if that gives you better idea, might be hard to say for sure wich one it is… being its and intermitten problem… I would also check for vacuum leaks not likely but vacuum leak might be causeing some other ramdum problem
sorry to say you might have to throw som parts at it just to test it… because its intermitit
also check your throtal spring and clean it might be that too.. should spriong open and shutt very fastOK. Thanks. I just found this thread. https://www.ericthecarguy.com/kunena/8-Service-and-Repair-Questions-Answered-Here/49715-help-with-cel-please
I took her out with the live data hooked up and it went into limp mode 3 minutes from my house. I was only watching the TP sensors and they look like they are correlating ok. I wasn’t looking at the APP sensors. Didn’t know to look at that until I read the thread above.
Going to go back out and see if I can get it to repeat the limp mode while watching TP and APP for correlation.
Just drove to work while having the live data running. And, of course, the car ran flawlessly.
The car didn’t go into limp mode but the readings from APP_D and APP_E did not seem to be the same. I know with the code reader there is some lag but it looked like the sensors were reading 1 to 1.5 % different from time to time. At zero throttle both read 0% though.
Here’s a question. If the fault happens while the car is in cruise control can I rule out the APP sensor since it is not functioning while in cruise control?
I am going to buy some automotive electronics cleaner and clean the contacts at the throttle, accelerator and PCM. See if that helps.
Thanks
Freeze Frame Data
DTCFRZF P1125
FUELSYS1 CL
FUELSYS2 — ?
LOAD_PCT(%) 35.6
ECT(C) 9.3
SHRTFT1(%) 0.8
LONGFR1(%) 0.8
MAP(kPa) 52.0
RPM(rpm) 2007
VSS(km/h) 96
SPARKADV(*) 28.0
IAT(C) 37
MAF(g/s) 21.18
TP(%) 21.6
EGR_PCT(%) 4.7
EGR_ERR(%) 3.1
EVAP_PCT(%) 72.5
FLI(%) 59.6
WARM_UPS 5
CLR_DIST(Km) 102
EVAP_VP(pa) -718.75
BARO(kPa) 101
CATTEMP11(C) 751.7
VPWR(V) 14.042
LAOD_ABS(%) 29.4
EQ_RAT 1.004
TP_R(%) 20.0
AAT(C) 35
TP_B(%) 22.0
APP_D(%) 14.6
APP_E(%) 15.7 ?
TAC_PCT(%) 20.8You most likely will need to replace the pedal, position sensor and then do a relearn / position calibration procedure to fix this.
Forgot to follow up on this.
I replaced the pedal assembly with one from the wreckers. Works no problem now.
Thanks
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