2007 Grand Prix in Limp Mode

Asked by TreyB_99 Jun 07, 2020 at 10:28 PM about the 2007 Pontiac Grand Prix Base

Question type: Maintenance & Repair

I've had this 2007 Grand Prix for a little over a year, but
shortly after I got it the transmission went bad so I had it
rebuilt. Shortly after, the car started going into limp mode.
I took it to a mechanic who said I had bare wires in the
main wiring harness, and he fixed it. A few months later, I
had the issue again, and when I had it scanned, the codes
indicated a gas pedal position sensor issue.  I replaced the
gas pedal assembly, but nothing changed. Fast forward to
today: I've replaced the throttle body, MAP sensor, and had
two harnesses rewired. Each fix usually resulted in the car
working for a while (even as much as 4 months) before I
get the same codes again.  Often, the car will go into limp
mode after hitting a bump in the road (even a small one),
but sometimes it just does it for no discernable reason or
will be in Limp mode when I start it. I've now spent over
twice what I paid for the car on repairs. What could
possibly be the cause of this issue?

1 Answer

18,645

It does sound like an electrical issue. Bad grounds, loose or corroded connections, even a weak battery can make modern cars do all sorts of weird things. I'm presuming whoever is working on your car is an expert on automotive electrical systems and fully understands how they work and how to trouble shoot them. (Not all mechanic/technicians do) If not, find one who does. I am fortunate to have such a person who often finds issues with my older vehicles. Its slow going even for him and my repair bill is often 50% diagnostic time and 50% actual repair. If you're a do it yourslfer, have your battery load tested to make sure its 100% strong, Locate all of the several ground points on your car and take them apart, clean everything, inspect the wires, reconnect and tighten them and make sure all wiring it properly tied in place and not flopping around. Scan in regularly for trouble codes, but even then don't just replace parts because they show as not functioning. Sometimes bad wiring or other issues will send a fault reading to the computer. There's lots of online info available that addresses each code and its many possible causes. Good luck. I know how terribly frustrating something like this can be.

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