2002 GP Auto Trans Slipping/not shifting

Well, I'm expecting the worst but hoping that there may be a simple explanation. My wife's 2002 Grand Prix with the 3.1L and only 37K mile suddenly had its transmission start slipping badly. It seems to only stay in one gear, and that gear does just feels like it's slipping any time you get on the gas. Reverse works fine though. This is kinda rediculous for a car with only 37K on it I think. Anyway, are there any known issues with this car that would cause a problem like this? Thanks.

Yes, the 4T65E tranny has known issues so expect the worse. Sounds like you need to get it to a tranny shop. Not much you can do DIY other than changing ATF and the screen filter. Do you have any extended warranty that will cover the transmission or see if the GM dealer will cover it since you are barely out of the bumper to bumper warranty. Good luck!

Well, I'm planning on taking it to the dealer anyway. They helped work with GM to get the intake manifold gasket covered when car was a couple months out of warranty. At this point, I'm probably going to have it towed because the slipping is rediculous. I don't trust it to make it the 8 or so miles to the dealer.

OK, now this is weird. I took it out again this morning to see what exactly it was doing, and I figured out that it wasn't so much slipping as it was just stuck in 3rd gear. Since it was stuck in 3rd, it couldn't take off well and felt like it was slipping. Anyway, just as I figured that out it started shifting through the gears like it should. At this point, I am hoping that it is a sensor or something that is off, but I don't know. The MIL is not on though. I'm going to let it cool off and see if it is behaving or not.

i wouldnt wait to long. where theree is trany problems always runs engine problems specialy if its slipping. in my old grand am that had the 4t65e trans. it slipped and i wound up putting it off putting it off then finaly i blew the engine because it over revved and i was dumb and didnt have a tach. so get it fixed asap. a trans problem is never something to mess with.

OK, now this is weird. I took it out again this morning to see what exactly it was doing, and I figured out that it wasn't so much slipping as it was just stuck in 3rd gear. Since it was stuck in 3rd, it couldn't take off well and felt like it was slipping. Anyway, just as I figured that out it started shifting through the gears like it should. At this point, I am hoping that it is a sensor or something that is off, but I don't know. The MIL is not on though. I'm going to let it cool off and see if it is behaving or not.

What does it do when you manually shift through the gears. Nothing worse than an intermittent problem. The PCM module controls shifting in auto mode based on engine and driving conditions. Not all tranny faults will generate a SES light but should store for retrieval by a transmission capable scanner. There are DTC fault codes to determine internal slipping, valve body, line pressure, pump and shift/pressure control solenoid problems.

What does it do when you manually shift through the gears. Nothing worse than an intermittent problem. The PCM module controls shifting in auto mode based on engine and driving conditions. Not all tranny faults will generate a SES light but should store for retrieval by a transmission capable scanner. There are DTC fault codes to determine internal slipping, valve body, line pressure, pump and shift/pressure control solenoid problems.

When it acted up, it would not shift gears regardless of where the gear selector was set. It was stuck in 3rd. As a result, it felt like it was slipping when taking off. Once it stopped acting up, it has shifted perfectly through all gears w/no slipping. It was even fine when cold this morning. We recently had some nasty snow here (Thursday), right before this started so I have to wonder if some moisture got where it shouldn't and temporarily shorted out something electrical.

That said, it would certainly still be a good idea to take it somewhere and have it checked for transmission codes. I'll see if anyone can get it in early next week. Would shops other than the dealer have the equipment to read the codes?

When it acted up, it would not shift gears regardless of where the gear selector was set. It was stuck in 3rd. As a result, it felt like it was slipping when taking off. Once it stopped acting up, it has shifted perfectly through all gears w/no slipping. It was even fine when cold this morning. We recently had some nasty snow here (Thursday), right before this started so I have to wonder if some moisture got where it shouldn't and temporarily shorted out something electrical.

That said, it would certainly still be a good idea to take it somewhere and have it checked for transmission codes. I'll see if anyone can get it in early next week. Would shops other than the dealer have the equipment to read the codes?

Hopefully you'll be OK and it was just a fluke. There is a GM TSB out on your model Grand Prix that says to make sure the 20/25 way connector is properly connected on the transmission. It is a big gray electrical plug located at the top of the driver's side of the tranny. All electrical signals/commands from the main fuse box, PCM and transmission range switch, etc. input there. With ignition off, you can disconnect it and then re-connect just to rule it out. Good luck!