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2003 Pontiac Grand Prix jerks and struggles when I run AC or heat?


I just recently bought a 2003 Pontiac Grand Prix GT V6 four door. After buying the car realized the dash and taillights were not working. I brought it back to the lot and they fixed the tail lights and dash lights. They said the box was just sitting on the frame and was shorting out wires but now was fixed.

Ever since this was fixed when I run the AC or the heat or defrost the car starts to struggle or jerk. Sometimes the Airbag light or the low oil level light will come on (the oil level is fine) and sometimes the gas gauge will drop a little, lastly it will sometimes stall when slowing down when pulling into a parking lot.

When I do NOT run the AC or heat the car seems to run and drive pretty smoothly in general. Yet sometimes I do get an air bag light come on or a little jerk when I slow down at the light or in a parking lot but nothing like when running the AC.

The mechanic at the car lot is stumped at what could be causing this. I think I need to find a new mechanic.

But anyone have a clue what would be causing this? A sensor? The car drove fine until the dash and taillights were fixed.


What are the odds that you can get out of this sale? That is your best bet.

If you’re stuck with it then, yes, you need a new mechanic. Preferably this would be a locally owned shop that has someone who is very good with electrical systems.

Whatever you do, you shouldn’t be driving it until you know why the oil light is coming on. The oil light has nothing to do with the oil level - it has to do with oil pressure. You can have plenty of oil in the car but low oil pressure. It will wreck the engine if there is an actual oil pressure problem.

If you can, return this car.

I cant return the car bought it as is with a 3000 mile (3 month) warranty… I have had it for a month. I need a diagnosis an to get it fixed.

I don’t think the oil light has to do anything with the oil just seems to come on only when the car acts up just like the airbag light (possible sensor electrical issue).The owner gave me $200 to take it somewhere to have to checked (since the mechanic there does not have a lot of diagnostics equipment)


One thing to know about the AC system is that it does produce a fairly hefty load on the engine since the engine has to run the compressor. It isn’t uncommon for a car that isn’t running quite right to stumble with the AC on. (This goes for the defrost - the AC compressor runs automatically on defrost so in either case you’re looking at running the AC compressor). The first things to look at for this kind of thing would be basic things like fuel pressure, spark plugs & wires, fuel & air filters.

However, given the prior lighting problems & weird behavior of dash lights & gas gauge in this case it seems likely that you may have a wiring fault of some kind. My first assumption would be a bad ground someplace. The first things that should probably be done are 1) double check the work done to fix the initial lighting problems; 2) clean the battery cable connections at both ends with special attention to the grounding points (wires leading away from the negative battery terminal); 3) load test the battery & charging system/alternator.

If none of that establishes anything then you do need someone who is good with wiring diagrams & electrical testing.

There is one more ground to check and it goes from the engine to the firewall or fender. It may need cleaning. On my pickup, it was connected to the transmission. 87 Mazda. A bad ground would stall a 79 Corolla when the AC was turned on.

What Cigroller says about the A/C putting a load on the engine is true, but it shouldn’t effect the engine on Heat.

Check the main engine wiring harness located near the front of the car, between the engine and radiator. Your car has a similar engine compartment to a Chevy Impala, and I can remember doing some wiring repairs to an Impala with a 3.8L exhibiting similar symptoms to yours in that harness. The damage was caused by the wiring harness sagging onto the exhaust manifold and thus being subject to much more heat than it was designed to tolerate. It’s sort of a shot in the dark, but worth looking into.

I also am suspicious about the “box” (presumably the fuse and relay center) that the dealer repaired. There may still be damage there the dealer did not catch, and your next mechanic needs to know about that.

thanks everyone so much for all the help!! I will look into all of these! thanks again!