oldred95

I've got a 2011 Silverado 2500HD that came in with a complaint of the check engine light being on and it shifts erratic. I scanned it and it had a P0796 pressure control solenoid 3 DTC. I go drive it and its got reverse, 1st, 2nd, 3rd, and thats it. When it shifts to 4th nobody is home. Commanding it through the gears with the tech 2 while stopped it will pull ahead in 1st, 2nd, and 3rd but not in 4th, 5th, and 6th. So I go down through the diagnostics for the P0796, pulled the TCM and solenoid assembly and air tested and all solenoids test good. Tore the valve body apart and all the valves float freely in the bore and when installed under spring pressure move and then snap back into their resting position crisp and cleanly when moved with a pocket screw driver. I didn't see any scoring or wear in the bores. So I pulled the tranny, tore it down and found the shaft made to what GM calls the 4-5-6 clutch hub was twisted and broken where it splines into the rear planetary assembly. The shaft is roughly 1 inch in diameter and hollow I'm guessing to lube the rear of the tranny. Anyway I replace the shaft. Pulled the 4-5-6 clutches out and they look fine. Pulled the piston out and no rips or tears. Put it back together and air tested it with the clutch assemblies all stacked up on the pump assembly so I was testing the fluid circuit from where the valve body mates to the pump clear up to the 4-5-6 clutch piston. It works perfectly and doesn't leak a bit. So I put it back together, put it back in and go for a drive. I noticed on heavy acceleration it had a slight flare on the 2-3 shift and a pretty noticable flare on the WOT 2-3 shift. Then I check the downshifts. Its got a violent 4-3 downshift. Tried it several times and it never got any better, possibly a little worse. Using the tap shift up and down the 4-3 is smooth as light throttle but if you floor it from 60 mph and do a WOT 4-3 downshift its a jolt but it does go ahead and shift down to 3rd. It feels like its going into two gears at once and I'm pretty certain this is what broke the shaft. Nobody said a word about it having a shifting concern prior to losing 4th, 5th, and 6th.

That being said this is not the first 6L80/90 I've seen doing this. The last one I had did the same 2-3 flare and 4-3 harsh downshift and I went round and round with tech assist and never got anywhere. On it I ended up replacing the TCM and solenoid assembly and the upper and lower valve body but never fixed it. It was a fleet truck and they needed it back so they got it back and I haven't seen it since. It is not the same truck as mentioned above. So the GM diagnostics and bulletins are no help and neither is technical assistance. I'm at a loss. I'm hoping some of you guys have seen something like this before and can point me in the right direction. I will say one thing when they work they are a durable bastard and have no problem living a life of hell but when they start this weird shifting problem I lose all respect for them. Sorry for the long read but I would really appreciate some help here.

01WS6/tamu

iTrader: (36)

Did you try doing shift adapt learn procedure w tech 2 after rebuild?
Did you try reflashing it to verify it has a OE tune in the TCM?

These new tranny's are trash can tranny's like a damm modern microwave when it breaks just scrap it unless you put a ton of time into doing a overhaul. We usually put a SRTA in them flash it and send it back out the door when they frick up just because they are so damm finicky when going through them. Then if it fails it's on gm to fix it and we get paid as opposed to doing it for free until it's finally figured out.

oldred95

No I didn't because I only replaced the one shaft and the fast adapt relearn isn't going to help this. I tried it on the last one that was doing this and it was a huge waste of time like every other time that I've done it. I didn't reflash it. It probably wouldn't hurt to verify but I know its got stock programming in it.

This is the third 6L90 I've had apart for a shift concern. The first one I ever messed with would neutral out at the top of 3rd gear. I had it apart 3 times, was on the phone with tech assistance I don't know how many times and replaced so many parts and never found a single thing wrong. It never would shift right. We finally got the ok to put a GM reman in it and the damn thing worked. That particular truck only had like 17,000 miles on it and the one I'm dealing with now only has 25,000 miles on it.

I've had a handful of blown up 4L60E's I've gone through and with those the problems are all visual and you replace what failed and they work. With these 6 speeds I've yet to find anything wrong accept for the case of the broken shaft and replacing it only revealed the underlying problem. I don't get it. I don't claim to be a tranny guy. All I want to know is enough to build up my 4L80E and thats it but nobody else will work on them so I get fucked over by these 6 speeds every single time.

built408

iTrader: (10)

Try doing the fast adapt relearn again, make sure you exit out of the procedure FIRST before you turn the key off. Unplug the Tech 2 and then turn key off. Wait 10 min or so then drive. If you don't exit out of the procedure first it usually won't take the relearn. I learned this the hard way.

I would reprogram it first anyway, I've seen this fix all kinds of problems in the past. Even if it doesn't show an update, program it anyway.

2011 has the updated pump cover and sealing rings, so your good there.

Did you check the 3-5-R clutches or piston?

And the 4-3 downshifts are usually always harsh, just an operating characteristic from what I've seen.

Good luck with it

built408

iTrader: (10)

Also, did you make sure all the check ***** are the correct size? Some are way undersized causing all kinds of weird issues.

Area47

i was under the impression the late 09- newer ones had the updated seals and pump cover?

built408

iTrader: (10)

Dec 08 is when the 2 piece started.

vagas3

Hi new to forum need some serious help have a 2012 chevy express van 2500 4.8L 6l90e.
Have all forward gears but no reverse. I have had the tranny out 2 times. Everything air checks thru the pump and thru the case. I have replaced 4 valve bodies, a new tcm and reflashed. Still no reverse. Help suggestions please....