# Grand Prix Reduced Engine Power **URL:** \ **Category:** Maintenance/Repairs\ **Tags:** pontiac, grandprix\ **Created:** [February 21, 2017, 6:45pm UTC](https://community.cartalk.com/t/grand-prix-reduced-engine-power/100261 "2017-02-21T18:45:04Z")\ **Posts on this page:** 16\ **Page:** 1
**Author:** ![ghibbits](https://avatars.discourse-cdn.com/v4/letter/g/49beb7/32.png) [@ghibbits](https://community.cartalk.com/u/ghibbits)\ **Post date:** [February 21, 2017, 6:45pm UTC](https://community.cartalk.com/t/grand-prix-reduced-engine-power/100261/1 "2017-02-21T18:45:05Z")
I have a 2004 Pontiac Grand Prix GTP with about 140k miles on it that goes into reduce engine power mode occasionally. I think it only does it going up hill, but not every hill. Repair shop said throttle body $900. I replaced it myself as well as the accelerator pedal sensor (due to the codes that pop up) and I am still receiving the same codes. (P1125 and P2138) What should be my next step? ---
**Author:** ![knfenimore](https://avatars.discourse-cdn.com/v4/letter/k/9fc348/32.png) [@knfenimore](https://community.cartalk.com/u/knfenimore)\ **Post date:** [February 21, 2017, 7:07pm UTC](https://community.cartalk.com/t/grand-prix-reduced-engine-power/100261/2 "2017-02-21T19:07:22Z")
Do you still have the reduced power or just the codes? Is your air filter clean? ---
**Author:** ![Mustangman](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/mustangman/32/44130_2.png) [@Mustangman](https://community.cartalk.com/u/Mustangman)\ **Post date:** [February 21, 2017, 7:31pm UTC](https://community.cartalk.com/t/grand-prix-reduced-engine-power/100261/3 "2017-02-21T19:31:09Z")
Did you reset the codes after the repair or just expect the car to erase them? They need to be reset. ---
**Author:** ![ghibbits](https://avatars.discourse-cdn.com/v4/letter/g/49beb7/32.png) [@ghibbits](https://community.cartalk.com/u/ghibbits)\ **Post date:** [February 21, 2017, 7:47pm UTC](https://community.cartalk.com/t/grand-prix-reduced-engine-power/100261/4 "2017-02-21T19:47:25Z")
I have reset the codes with the reader. I haven’t checked the air filter myself, but my wife took it in for an oil change since this started happening. I would hope they’d check that. I’ll check tonight. I’ll get the reduced power and the codes now. “check stability” light has popped on when this occurs, but not every time. ---
**Author:** ![NYBo](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/nybo/32/17281_2.png) [@NYBo](https://community.cartalk.com/u/NYBo)\ **Post date:** [February 21, 2017, 11:14pm UTC](https://community.cartalk.com/t/grand-prix-reduced-engine-power/100261/5 "2017-02-21T23:14:17Z")
Have a sunroof? Any water in the driver’s footwell? If so, take a look at this: > [@Rain, rain, go away!](https://community.cartalk.com/t/rain-rain-go-away/96241): > > The other day, my wife told me there was something wrong with her car (2012 Chevy Malibu). The “Check Engine” light was on, the odometer area was reading"engine power reduced", “service ESC” , and “service traction control.” The only error code was P2138, a throttle-by-wire error. There was water on the headliner and floor, and the storage bin on the dash next to the driver’s door was completely full of water. Fearing the worst, I made an appointment with my mechanic. But I also did some sea… ---
**Author:** ![ghibbits](https://avatars.discourse-cdn.com/v4/letter/g/49beb7/32.png) [@ghibbits](https://community.cartalk.com/u/ghibbits)\ **Post date:** [February 21, 2017, 11:40pm UTC](https://community.cartalk.com/t/grand-prix-reduced-engine-power/100261/6 "2017-02-21T23:40:35Z")
It does have a sunroof but I don’t feel any water inside the car. The air filter was clean. ---
**Author:** ![George\_San\_Jose1](https://avatars.discourse-cdn.com/v4/letter/g/e5b9ba/32.png) [@George\_San\_Jose1](https://community.cartalk.com/u/George_San_Jose1)\ **Post date:** [February 22, 2017, 4:34am UTC](https://community.cartalk.com/t/grand-prix-reduced-engine-power/100261/7 "2017-02-22T04:34:38Z")
Do you notice any engine pinging when going uphill? That can sound just like its name, a “ping” noise, often not very loud, that increases in frequency the faster the engine is going. Or if it gets worse, it can also sound louder, and like someone is rattling a metal soup can filled with nickles in the engine compartment. A quite noticeable clattering sound in other words. Does your car use a ping or detonation sensor? ---
**Author:** ![ghibbits](https://avatars.discourse-cdn.com/v4/letter/g/49beb7/32.png) [@ghibbits](https://community.cartalk.com/u/ghibbits)\ **Post date:** [February 22, 2017, 3:08pm UTC](https://community.cartalk.com/t/grand-prix-reduced-engine-power/100261/8 "2017-02-22T15:08:22Z")
I haven’t heard any pinging. I’m not sure about a ping or detonation sensor. ---
**Author:** ![pete\_peters](https://avatars.discourse-cdn.com/v4/letter/p/46a35a/32.png) [@pete\_peters](https://community.cartalk.com/u/pete_peters)\ **Post date:** [February 24, 2017, 3:34pm UTC](https://community.cartalk.com/t/grand-prix-reduced-engine-power/100261/9 "2017-02-24T15:34:09Z")
Check wiring at pedal assembly, throttle body, and PCM. ---
**Author:** ![the\_same\_mountainbike](https://avatars.discourse-cdn.com/v4/letter/t/c89c15/32.png) [@the\_same\_mountainbike](https://community.cartalk.com/u/the_same_mountainbike)\ **Post date:** [February 24, 2017, 3:38pm UTC](https://community.cartalk.com/t/grand-prix-reduced-engine-power/100261/10 "2017-02-24T15:38:04Z")
Have you checked for an exhaust restriction? ---
**Author:** ![NYBo](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/nybo/32/17281_2.png) [@NYBo](https://community.cartalk.com/u/NYBo)\ **Post date:** [February 25, 2017, 2:02am UTC](https://community.cartalk.com/t/grand-prix-reduced-engine-power/100261/11 "2017-02-25T02:02:06Z")
Check that connector on the end of the dash on the driver’s side for moisture anyway. ---
**Author:** ![ghibbits](https://avatars.discourse-cdn.com/v4/letter/g/49beb7/32.png) [@ghibbits](https://community.cartalk.com/u/ghibbits)\ **Post date:** [February 26, 2017, 8:29pm UTC](https://community.cartalk.com/t/grand-prix-reduced-engine-power/100261/12 "2017-02-26T20:29:06Z")
My wife started backing out of the driveway and it started to shake. A new code popped up, along with the other two. P0128. How would I check for exhaust blockage? I don’t believe the o2 sensors have ever been replaced. Curious if those and cat should be replaced for this? ---
**Author:** ![the\_same\_mountainbike](https://avatars.discourse-cdn.com/v4/letter/t/c89c15/32.png) [@the\_same\_mountainbike](https://community.cartalk.com/u/the_same_mountainbike)\ **Post date:** [February 26, 2017, 11:08pm UTC](https://community.cartalk.com/t/grand-prix-reduced-engine-power/100261/13 "2017-02-26T23:08:25Z")
> [@ghibbits](#): > > How would I check for exhaust blockage? With a vacuum gage. > **[Vacuum Gauge Tests - Car Repair Information From MasterTechMark](https://www.certifiedmastertech.com/251/vacuum-gauge-tests/)** > > How to use a vacuum gauge to diagnose leaking EGR valves and restricted exhaust systems. The vacuum gauge is a valuable tool for this diagnostic test. ---
**Author:** ![ghibbits](https://avatars.discourse-cdn.com/v4/letter/g/49beb7/32.png) [@ghibbits](https://community.cartalk.com/u/ghibbits)\ **Post date:** [February 27, 2017, 6:07pm UTC](https://community.cartalk.com/t/grand-prix-reduced-engine-power/100261/14 "2017-02-27T18:07:28Z")
I broke down and took it to a shop. They said I need to take it to the dealer and have them program the throttle body. Is there a way I can do this, or just have dealer do it? Also, does the accelerator pedal sensor need to be calibrated or reset? ---
**Author:** ![Nevada\_545](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/nevada_545/32/41232_2.png) [@Nevada\_545](https://community.cartalk.com/u/Nevada_545)\ **Post date:** [February 27, 2017, 6:31pm UTC](https://community.cartalk.com/t/grand-prix-reduced-engine-power/100261/15 "2017-02-27T18:31:57Z")
Those fault codes relate to the accelerator pedal position sensor, nothing to do with the exhaust system. As mentioned before the wiring and connectors should be closely examined and tested, it may be worth the money to have an experienced technician repair this. P0128 is related to the coolant temperature being too low, the thermostat may not be closing/sealing properly. ---
**Author:** ![ghibbits](https://avatars.discourse-cdn.com/v4/letter/g/49beb7/32.png) [@ghibbits](https://community.cartalk.com/u/ghibbits)\ **Post date:** [March 3, 2017, 5:38pm UTC](https://community.cartalk.com/t/grand-prix-reduced-engine-power/100261/16 "2017-03-03T17:38:42Z")
It appears to have been a defective accelerator pedal sensor in the one I replaced. Bought a pedal from the dealership and it’s been working so far (knock on wood). That’ll teach me to buy car parts on Amazon…