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Discussion Starter #1
Hi, have 2007 Grand Prix and the other day the " reduce engine power light came on and the engine light. Only thing i have done so far was clean the throttle body a little, which was not dirty really. After putting back the intake boot the light was on as i started the car. I went a mile away at slow speed and pulled into a packing lot and waited one minute after shutting off the car. After restarting, it was fine but the engine light was still on so i was going to have it read the next day, I had no problems the next day and by the end of the day the engine light went off on its own, so i figured all is well, the car ran fine for another day and then today it started all over again. some times it controls my speed and other times not. The engine light is back on........is this a connection problem? or what? Thank you in advance. Bob.
 

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You need to scan the computer controls and check the CODES. This will shed some light on the problem. You will need to use a scanner to see this info.

Jake
 

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I was looking at one of my tech sites and it appears your car has an electronic throttle assembly. IF THIS IS THE CASE, your issue may be a bad ELECTRONIC THROTTLE ASSEMBLY. If this is the case, you may need to replace that unit. Also, check the wiring going to that assembly to be sure it's connected properly. And, it's important there are no tears or unhooked tubes going to the air intake duct and there aren't any tears or air leaks in that air intake duct. Guess that's about all I can find for now. Jake

Keep us up dated on this issue if you can.......
 

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I was doing a bit more searching on that issue and found out there's a control module on the throttle assembly. This could also be a problem like you described. Jake
 

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Discussion Starter #6
Everything points to throttle position sensor. MAF, MAP, From what i read
, thanks , i will check the things you listed some again, parking car until its fixed
 

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If you were cleaning the throttle body , I am guessing you had some stuff unplugged ?

I suggest you go back and tripple check all that electrical and / vacuum devices .

Wyr
God bless
 

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If you were cleaning the throttle body , I am guessing you had some stuff unplugged ?

I suggest you go back and triple check all that electrical and / vacuum devices .

Wyr
God bless
 

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Discussion Starter #9
I took off the throttle body and cleaned it more, I think my issue is with the accelerator pedal position sensor or the wiring coming from it. All the symptoms point to it and the code p1125. I hate just buying parts but i am going to recheck my wires and if i dont find anything im buying the pedal sensor for about $100 from advanced auto. I m also looking into buying an OBDLink MX+ too , $80.00 , looks like a nice product and i can check my own stuff and do resets too, plus monitor some systems as i drive. Thanks for the inputs.
 

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Discussion Starter #11
Yeah, I am a speed perk member, and as you know they always offer a 20% discount too. Plus if you have it delivered and have to return something you can just bring it back to the store. I still haven't worked on it yet , im fortunate to have other vehicles to drive but hopefully this weekend, i also have a code reader on the way too, so i can reset the codes and see if any pop back up. The other day i started it, drove it and no issues for the day, then the next day it started again.
 

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Re: Reduced Engine Power

I recently went through this entire routine on my daughter's '04 Grand Prix GT with non-SC 3800. Initial issue was no code, but engine "hunting" for correct idle speed when idling. Replaced the throttle Body and all was fine for about 6 mos until getting the dreaded: Reduced Engine Power.

Car was throwing codes: PO1125: Intermittent TPS signal; PO2120: TPS reading out of Range.
Couldn't just replace the accelerator pedal sensor - You have to replace the entire accelerator pedal assembly. ~$100. Replaced with a new Standard Motor Products (SMP) unit and the problem cleared for 4 days, but then the exact error codes and Reduced Engine Power returned. I could reset the codes and the car would be OK a day or two, but Reduced Engine Power and codes always returned. As the Throttle Body and Gas Pedal Ass'y were new, thought I likely had a bad harness. Carefully tracing all the wires, all checked good. I could clear the codes and wiggle/shake the harness and not get any errors, but drive the car and it would randomly happen with no correlation to speed, temperature or terrain. As the car was now totally unreliable and unsafe to drive on freeway with reduced power, we took it to the GMC dealer we periodically use. The tech showed me how his scanner read the data frames on the computer and it clearly showed an intermittent signal coming from the new Accelerator Pedal unit. They replaced the SMP accelerator pedal with a new OEM/Delco unit. Following replacement, they monitored the TPS signals while wiggled and shaking the harness just to make sure there wasn't a loose connection. The signal remained rock solid, no intermittent signals. The car is driven daily and has been working fine now for the past 6 mos without a glitch! I returned the SMP unit and sucked up the $340 the dealer had charged me for parts and labor. A lesson learned, albeit costly!

For these critical systems, I'll now always spend the few extra $$ for OEM parts. Has been so worth it to have a reliable car again. Hope this helps!
 

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Discussion Starter #14
Hi Bigolotava, Thanks for the info, since i haven't solved it yet mainly because i just didn't have the time yet and have another vehicle to drive. But i noticed it can work just fine for one trip and hop in for another trip 30 minutes later and it starts all over again. Do you know the cost of just the part you bought with the dealer? My original plan was to buy it at advanced auto but now i may buy OEM. I still haven't checked my wires yet also. Seem if it works one minute and not the next that sounds more like a connection or if the sensor heats up it expands and breaks a connection some how. Thanks again, Bob
 

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Re: Reduced Engine Power

Bob - Sounds like its doing the identical thing. Our car would run fine for days, minutes or any random amount of time in-between. Other times it would happen several times in a half hour. Just didn't know when it would happen, but really scary for my daughter when she was driving on the freeway and all at once the warning lights come on, the chime starts going off and power diminishes to where she could only go 30mph with the pedal to the floor. The message boards and websites are full of horror stories about people replacing wire harnesses, ECU's trying to fix this and still have the problem. (common issue on lots of GM cars, not just our 3800's)

Rock Auto sells the accelerator pedal assembly: AC Delco part#25830024 for $69.95. The GMC dealer charged me $135, plus $170 labor. Being able to view the data on their scan tool was really helpful and also restored my confidence in the car. Still took several months of trouble-free driving before we really started trusting the car again. We still keep our code reader in the glovebox in case it ever happens again so we can reset it, but at 6 months out I'm calling this permanently fixed. It sucks when you buy new parts and even they are faulty! As mentioned earlier, will stick with AC Delco for mission-critical items like this from here on out.

Do be sure to disconnect the (-) battery terminal when you replace this. You can damage the computer if you don't. Once you've replaced the accelerator and reconnected the battery the ECU will need to "re-learn" the signals from that new TPS in the accelerator pedal. Start the car and let it idle a minute or two. The RPM will hunt around, but will settle back down. The ECU is learning. Turn off the ignition, wait 30 seconds, then restart. Now drive the car, but be sure to accelerate above 45MPH so the ECU relearns the upper end of the new TPS's range. Once you've done this you're good. Mine laid rubber the first time I pulled away from a standing stop!

Do let us all know how this turns out for you!
 

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Discussion Starter #16
Thank you so much for taking the time to respond, I think our situation is the same and I will buy the AC Delco part after reading your story from rock auto, actually cheaper than where is was going to buy the aftermarket one. . I am going to check the wires first too. I just bought a code reader for the first time too so I am going to reset and start all over since I cleaned the TB and never have reset the codes. I am almost sure my issue in the same as yours. Also I have had real battery connection problems in the past and I wasn’t going to disconnect the battery because I haven’t had that issue in a long while but now I will listen to your advice too to disconnect the negative. I am glad you mentioned that. I look forward to driving my car again and hope this will fix it. I totally understand about being worried about your daughter driving the car, I am getting used to it now but getting on the highway would be disastrous, mine seems to have two modes, sometimes its like driving a golf cart as far as power goes and sometimes it is a little more powerful to drive and as I said sometimes it even drives like normal. Also thanks for the advice when getting the computer to relearn the new part, that will help me when I finally get this fixed. I will post my final results here so anyone else can read this and hopefully help them too. Bob.
 

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Discussion Starter #17
OK I hooked up my new code reader and cleared all the codes. I drove 8 miles and ran fine no engine light . drove it again after 4 hours and it almost instantly threw P1125 and P2138 so i cleared it twice and same codes right away. So both indicate pedal sensor when combined. Ill check the wires and connector as im pulling the pedal and under the hood. Buying OEM part as you said. Thanks again. BTW i found another video stating a doorman pedal failed on install and he too advised only dealer parts OEM. That info probably will save me and others who read this a lot of time. I'll post the results.
 

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Bob - Glad you got the code reader and were able to confirm the codes. You can check the wiring by starting the car, clearing any codes, then gently, but deliberately moving/wiggling the harness at the throttle body plug, following it towards the firewall and at the wires coming from the accelerator pedal plug. If you can do that and no codes get thrown in the process, the wiring harness is not likely the culprit. Looking forward to reading how well your '07 does with the new AC Delco accelerator ass'y - Kevin
 

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Discussion Starter #19
Thanks Kevin, Great idea, i hate checking wires. I once had a Bonneville that when you barely moved the wire harness for the fuel pump located under the hood, fuel pump in the tank, the fuse would blow.....of course i didn't realize this or my mechanic at the time before many tows and a new fuel pump, I figured it out my self before you tube and the internet forums. any way i cut all the wires on both sides of the harness and soldered them and never had a problem after that. Thank God for the internet and people willing to share info. now. meanwhile on this car I have been driving the car since i last posted but i am not going to drive it anymore until i get it fixed, going to pull the pedal this weekend and order the part so ill let it sit until next weekend. I found a video i thought people would like to see concerning this issue and checking the TB , Link is below, its a long video but worth watching......

https://www.youtube.com/watch?v=IYm2C7zr82Q
 

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Having a code reader and being able to clear them makes all the difference in the world. I bought one for $20 at Walmart. It's not high tech but it get the job done.
 
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