99GTP Transmission Issue P0756

[SupraDan]

Hi all, I'm hoping someone here can point me in the right direction with the transmission issues I'm having.

I have a 99 Grand Prix GTP and for the past couple of weeks it had an issue where if I was driving along at about 30-40mph and 1700rpm it would feel like the torque converter was locking and lettting loose over and over ( rpms would 'bounce' by about 300 up and down) until I let off the gas, then i could go back to normal driving. I assumed it was the TCC solenoid and I'd


Well yesterday it gave up, seems like it's never locking up, I'm not even sure if it's shifting, from what I'm reading it may just be in 3rd. 55mph is almost 4000rpm.


The only code I'm getting is P0756 2-3 Shift Solenoid Valve Performance.


My current plan is to replace the solenoids, shift - and TCC as long as I'm in there. Is that a good plan? Are the solenoids for the 4T65E the same as the ones for the 4T65E-HD? (99 GTP all have the HD right?)


Anyone who's seen this problem before, was it just the solenoids? I don't want to get it torn apart and realize I need to source a whole new transmission. It's currently my daily driver and only car.


Also, does anyone have a how-to on how to on dropping the transmission down and doing this job? Any shortcuts or tips? Going to be doing this in my driveway (hopefully no snow) since my summer car is in my garage taking up my lift with no engine in it currently.


If I stay off the highway and try to keep it to <50mph on surface roads is it killing anything by driving it while I wait for parts?


Sorry for the long post, thanks for any help or stories or tips you Grand Prix veterans might have

[Scottydoggs]

http://ricksfreeautorepairadvice.com...e-gm-vehicles/ google gave me this info.

[BrandonHall10]

^^^ Just skimmed that article.

I was going to say, I'd be surprised if it was the solenoid itself. More likely the VB is full of junk, causing a sticking valve. You could clean it and be okay, BUT...

You need to know where the crud is coming from. Is it normal clutch material, or is it coming from the TCC...? If it's clutch material, a pan drop and fluid change will buy you a lot of time. If it's the TCC, you're kinda hosed.

[SupraDan]

Thanks for the replies. Oh man, I'm really hoping it's just a solenoid but from what you've said and the googling I've done since last night it seems the shift solenoids don't actually go bad very often.

At the moment I'm leaning towards replacing the solenoids and cleaning up the VB and hoping for the best - the car has 178K miles on it now, I'd like to wait until spring to replace it so you think just cleaning it all up and replacing the solenoids might get me another couple of months of daily driving?

If it is the TC going do my problems sound like it's at the end of the road or do you think I could clean it all up and baby it for a few months?

Thanks again

[Scottydoggs]

if your gonna wait till spring i hope you plan on parking it till then.

[BrandonHall10]

I can't say for sure how long it would last, but it's worth a shot, right?

Pull the VB, get it super clean. Clean the CP while it's apart. Drop the pan. Change fluid and filter. Load the pan with magnets. That will (help) keep the grit out of the VB.

FWIW, dark grey paste = clutch. Black grit = TCC.

Here's the pan from a failed TCC:

[SupraDan]

Awesome, thanks for that, definitely going to change the filter and fluid while I'm going through all of this.

ScottyDoggs: Oh, I'm planning to attempt fixing this problem in the next week, I meant I'm going to replace the whole car in the spring.

[Scottydoggs]

oh, got ya lol new cars are always nice. as long as its not a load of problems like most used cars are.

[SupraDan]

Yeah, the Grand Prix has been great for the past few years, bought it used, put almost 100K on it and it was trouble free until it hit 170K and, like a switch was flipped, since then it's been one piddly thing after another... I was hoping for one more winter before something big (like the transmission) gave up on me.

[paedbo]

If you know how to use a multimeter you can check the resistance readings on the solenoid to find out if it has an electrical problem.

[SupraDan]

So yesterday I spent the day replacing the 4 solenoids and pressure switch and I pulled the pan and replaced the filter. The old oil was all brown but there was almost zero sediment in the pan. Could be the first time the transmission oil was changed in its 176K mile life...

Got everything bolted back up and have the same code and the same problem. The wiring checks out fine (plus I'd get a code p0758 if the wires were broken/shorted) so I'm at a loss.

Only thing I can think is that something downstream of the solenoid is preventing a shift from 2nd to 3rd so the computer thinks the solenoid is stuck off?