2002 Grand Prix jerks when shifting

My 2002 Grand Prix jerks when shifting. It originally happened earlier in the spring but fixed itself after I had a coolant leak fixed. Now it’s happening again. The coolant and ATF levels look okay. I found one possible fix on Google but wanted to get some other opinions first. Any ideas what’s wrong, or how urgent it is? Is this something I might be able to fix myself without a lot of trouble?

Gen, Is The “Check Engine” Light On Or Has It Been On Recently ?

You might try stopping by a neighborhood national chain type auto parts store. Many will check your car’s computer for diagnostic trouble codes, free of charge. Write any codes down exactly as presented (like PO123, etcetera). Post them here.

DTCs (codes), if any are being stored, can offer clues that can help zero in on the cause of the problem.


Thanks for the recommendation. I stopped by O’Reilly’s this morning and had the codes checked, but the guy said his scan tool wasn’t showing any codes, and that the check engine light would come on if any codes had been thrown–and I forgot to mention earlier that I haven’t seen the check engine light come on.

My wife was driving the car around town with me earlier this morning and she didn’t notice any jerking, but after I dropped her off and drove it home for lunch immediately afterward, I noticed that it was jerking when shifting from 1-2 and 2-3. I was just driving in town, so didn’t get going fast enough for it to shift any more than that.

The Chevy dealer says it will cost up to $80 to diagnose the problem.

You may need to get it onto a code reader that will read the manufacturer specific codes (anything from P1000 and up). If this is anything like my '00 Olds - which it probably is, there can be codes, including transmission codes, that won’t turn on the engine light. The auto parts stores in my area have code readers that only read generic codes (P0999 and under).

I would pull it into your best local transmission shop & have then check it out. I already have my guess, but there’s no point in sending you off on something without any codes.

Thanks, the guy at the parts store wasn’t very clear on that point. Is $80 at the GM dealership a reasonable diagnosis fee, or should I be taking it to an independent shop?

It’s a reasonable cost for a dealer diagnosis. If you then have them perform the repair, normally they will throw the into the bill (reduce the bill by that amount).

The advantage of using a dealer for this type of work, is the one cost is what you’ll pay, whether it takes them 10 minutes, or 4 hours. They’ll also check the entire vehicle, whereas most independents will check their specialty areas, and if it’s not in their area, you may have to go somewhere else.

I can’t be certain, but an independent may charge by the hour (and rightfully so, they have bills, too). Maybe someone else has a differing opinion. You could always call around and ask questions. I think the phone calls are still free. :slight_smile:

Thanks chaissos, we took it to the dealer yesterday after calling around and getting some other quotes on the diagnosis. Of course, the diagnostic fee of “up to $80” ended up meaning, “$80.”

Okay, the code is P1811, and the part they want to replace is the same one I diagnosed just by searching for the symptoms on Google… The dealership quoted me about more than $1000 for the repair, which includes a $200 transmission flush even though I just had that done within the past year. One independent shop quoted $800, and another one is going to look at it tomorrow (we already gave them the diagnosis, so I’m not sure why they need to look at it before giving a quote).

Without cheating, does anyone want to guess what’s causing the problem?

They think it is the EPC solenoid. In fact, at this point the “legend” is that if your GM with a 4T65E transmission throws a P1811 that this code “means” EPC solenoid.

Far from it. P1811 means that the shift time is too long. (It often reads “max adapt long shift”). The computer watches the time it takes to go from one gear to the next. The length of time indicates the amount of slipping (some is good, too much is bad). When the shifts take too long it ups the line pressure to speed the shift. And will keep doing that…until it hits is “max.”

Once it sees this it sets the 1811 and just completely maxes out line pressures - thus you probably hear a whine down in low gears and you get this hard shifting. Then you can probably turn the car off sometimes and it goes back to normal the next time you start it…only to return.

I refer to the EPC solenoid as a “legend” because this is a very common problem in the 4t65E’s. Early on GM put out a TSB specifying a faulty EPC solenoid as the issue. However, there is a significant number of cases in which this doesn’t help and faith in that diagnosis has disappeared.

There are quite a few things that produce the shift time problem - including worn clutches which can only be addressed by a full rebuild. You never said how many miles are on this car or anything about the service history so its hard to guess. Its practically impossible to guess anyway since really figuring it out requires an experienced tech on a fancy scanner. Even then I don’t know that I’d trust an actual diagnosis for this issue. Ask the to give you details on how they verified their diagnosis.

I have a 4T65E in my Olds Van. It used to do that. No one could (or would) tell me anything about it. They just wanted to order a reman for it. I actually had one transmission shop guy tell me the 1811 was set BECAUSE the line pressures were too high. I left about 10 seconds later.

I did this: http://www.grandprixforums.net/4t65e-hard-shift-solution-25211.html
That was the end of my hard shifting.

Note that I hate this van. If I liked it I would find someone who knew their ear from their elbow to fix it the right way - except even that can be ambiguous since a lot of people who do know these transmissions install the shift kits referenced in that discussion thread whenever they rebuild one.