6L80 - P0776 Error + No Move Condition

[08ColoRADo]

Reaching out into the HPTuners universe for help and guidance regarding some electronic trans nonsense.

Quick Rundown:
2008 Colorado - Full Tube Chassis - Custom Everything - Big Tires - Big Axles - Rock Crawler
Gen7 BBC - 8.1L Vortec Motor - Holley Terminator engine management - Runs great
2008 Escalade - 6L80 Transmission - TCM2650 Transmission Controller - Not So Great currently.

I bought the transmission a few years ago knowing that it had been pulled out because it lost reverse. This past May I finally got around to rebuilding it. All new steels and clutches, rubber pistons and seals throughout, filter, fluid, etc... Throw the trans in and hook up the TCM2650 to it. Start it up and drop it into drive, No movement. Drop the pan and discover that I had left the plastic shift lever off the external lever and it wasn't getting pushed into the valve body so it wasn't demanding any gear. Fix that, and now I can watch it demand each gear as appropriate, but still no movement. My only error code is a P0776 Error - Pressure Control Solenoid B Performance/Stuck Off (permanent.)

Using HPTuners I can see the transmission input speed matching rpm and it's showing 0 output speed and 100% transmission slip. Obviously it has no rear tire movement regardless of throttle input. Before I throw money at a new TCM/valve body, can anybody give me a different idea of what to look for/try for a repair?

Searched the forums and only three threads showed up with a similar code, the two regarding 6l80s both still had tire movement and it was driveable, only in certain gears.

Anybody have any ideas?

[08ColoRADo]

Checking back in, doesn't look like there's any feedback on this. Looking into getting a tech 2 and running a solenoid cleaning procedure. If that doesn't work maybe a new TECHM.

[Estep40511]

I would say its either a stuck valve in valve body or the weld is broken on the 4-5-6 hub/shaft. Could possibly be the pump is out, scored body or rotor vane. But more likely the valve body. You can take it out and see if you have a valve stuck first.

[Estep40511]

also, since it was rebuilt, possible you could have a retaining ring not seated all the way. Making a clutch pack over travel.

[08ColoRADo]

Thanks for the suggestions. Logging back into this to say that my Tech 2 arrived yesterday and I should hopefully be able to get more information whenever I have the opportunity to plug in this week and examine what's what. Crossing my fingers for something simple that a solenoid cleaning can fix.

[TransGo Robert]

Thanks for the suggestions. Logging back into this to say that my Tech 2 arrived yesterday and I should hopefully be able to get more information whenever I have the opportunity to plug in this week and examine what's what. Crossing my fingers for something simple that a solenoid cleaning can fix.

Coming in late on this one, joined this forum only recently. First thing to try is to see if you have any movement with the transmission harness disconnected. If you don't then put a pressure gauge on it and see if you have any line rise at all. No line rise you will get no engagement on a 6L80. The scanner data is not really going to help you much on this.

[08ColoRADo]

Updates!

Put the Tech 2 on it and manually actuated the solenoids a few times to ensure they functioned. They appear to. Started the rig up and used the Tech 2 to manually select a gear (I don't have manual mode engaged on my shifter currently). 2nd through 6th all appear to function normally. So we have wheels spinning for the first time on this build!

If you downshift to 1st gear from 2nd it will keep spinning for as long as you don't brake. You brake and it stopped and won't start again.

Won't go into reverse or 1st and start spinning no matter how much throttle you give it.

Any thoughts?

[TransGo Robert]

Updates!

Put the Tech 2 on it and manually actuated the solenoids a few times to ensure they functioned. They appear to. Started the rig up and used the Tech 2 to manually select a gear (I don't have manual mode engaged on my shifter currently). 2nd through 6th all appear to function normally. So we have wheels spinning for the first time on this build!

If you downshift to 1st gear from 2nd it will keep spinning for as long as you don't brake. You brake and it stopped and won't start again.

Won't go into reverse or 1st and start spinning no matter how much throttle you give it.

Any thoughts?

Your controller must not be applying the L/R when you command first gear, it sounds like your sprag is not holding. CHeck to see if it commands the L/R or not, if not pull it out, the sprag is not holding. If it is commanding then L/R then put a gauge on it.

[08ColoRADo]

Forgive my ignorance as I'm mostly transmission illiterate and am learning as fast as I can. The symptoms as I describe match a lot of others issues online and the low range sprag does appear to be a potential culprit.

I didn't notice anywhere on the Tech 2 to determine if the module is commanding L/R. I'll put the HPTuners module back on it after lunch and look to see if that has a spot to see engagement.

[TransGo Robert]

Forgive my ignorance as I'm mostly transmission illiterate and am learning as fast as I can. The symptoms as I describe match a lot of others issues online and the low range sprag does appear to be a potential culprit.

I didn't notice anywhere on the Tech 2 to determine if the module is commanding L/R. I'll put the HPTuners module back on it after lunch and look to see if that has a spot to see engagement.

Yea you will see it on the log. The way it is supposed to work with stock file is the low reverse are applied on take off and then releases at 3 mph. After that you are on the sprag only until you get to second gear or above.

[08ColoRADo]

Yea you will see it on the log. The way it is supposed to work with stock file is the low reverse are applied on take off and then releases at 3 mph. After that you are on the sprag only until you get to second gear or above.

Looking at the log and not seeing anything LR related. I have every channel selected available. I have PCS 1-5 Selected as well as oncoming clutch and clutch shift type.

Other posts I'm reading are relating individual pcs pressures to the low/reverse sprag turning on/off. Also, I saw a few posts discussing L/R tuning to be able to almost eliminate the sprag usage at all. Is that a possibility to help preserve it's function?

[TransGo Robert]

Looking at the log and not seeing anything LR related. I have every channel selected available. I have PCS 1-5 Selected as well as oncoming clutch and clutch shift type.

Other posts I'm reading are relating individual pcs pressures to the low/reverse sprag turning on/off. Also, I saw a few posts discussing L/R tuning to be able to almost eliminate the sprag usage at all. Is that a possibility to help preserve it's function?

PCS 3 is the solenoid in charge of applying and releasing the L/R 4-5-6 brake.

[08ColoRADo]

PCS 3 is the solenoid in charge of applying and releasing the L/R 4-5-6 brake.

Thanks for the clarification. Well in my most recent log it shows PCS 3 CMD pressure at 0 PSI in reverse, 110 PSI in neutral, 110 PSI in D6 "Drive", and then as I command 2nd gear and it shifts, PCS3 Shows 0 PSI.

I can post the log if that will make it easier. But does this sound normal for trans function and still pointing to replacing the sprag gear?

Thanks for all the help TransGo Robert.

[TransGo Robert]

Thanks for the clarification. Well in my most recent log it shows PCS 3 CMD pressure at 0 PSI in reverse, 110 PSI in neutral, 110 PSI in D6 "Drive", and then as I command 2nd gear and it shifts, PCS3 Shows 0 PSI.

I can post the log if that will make it easier. But does this sound normal for trans function and still pointing to replacing the sprag gear?

Thanks for all the help TransGo Robert.

Yes do post the log, it will definitely make it easier. Just a quick recording of it in regular OD range giving it gas for a few sec trying to move forward.

[08ColoRADo]

Yes do post the log, it will definitely make it easier. Just a quick recording of it in regular OD range giving it gas for a few sec trying to move forward.

See attached log. Placed in Drive, attempted to give throttle with no response. Manually selected each gear and you can see the response from the trans output shaft RPM. One thing I'll also note, and I don't know if I'm reading into this too much. The speed doesn't increase as I demand other gears. It almost looks like it's never leaving second, despite saying that it's shifting.

08-30-23 Trans Log - All Gears Manually Selected.hpl

[TransGo Robert]

See attached log. Placed in Drive, attempted to give throttle with no response. Manually selected each gear and you can see the response from the trans output shaft RPM. One thing I'll also note, and I don't know if I'm reading into this too much. The speed doesn't increase as I demand other gears. It almost looks like it's never leaving second, despite saying that it's shifting.

08-30-23 Trans Log - All Gears Manually Selected.hpl

Ok it is not the sprag, something else is going on. Weird that it did not record you engine RPM and TPS and also strange that your OSS does not go more than 260 RPM no matter what once it goes to second gear, it does not seem to be shifting at all, if the ISS matches the engine RPM it looks like once it goes to second gear it just stays in second no matter what the command is.Also PCS5 remains ON even when it says it is commanding 4-5-6 when it should be OFF. Not sure what you have here, but it sounds like some sort of corrupted programing to me.

[08ColoRADo]

The reason that it looks so weird is probably because the trans is being controlled via standalone on a TCM 2650.
The engine is being controlled by a Holley Terminator, so there won't be any engine parameters coming through to HP tuners, as it's solely reading the trans.
I didn't give it any throttle once I commanded second gear or the other gears. I only gave it throttle when I was in drive, and it wanted the trans in first.

Should I try and put it in drive, command second, then turn off the command for second, and see if it will shift with throttle?

Additionally, the trans shouldn't have any unusual programming going on to my knowledge, it was pulled from a stock 09' Escalade that had reverse issues.

[TransGo Robert]

The reason that it looks so weird is probably because the trans is being controlled via standalone on a TCM 2650.
The engine is being controlled by a Holley Terminator, so there won't be any engine parameters coming through to HP tuners, as it's solely reading the trans.
I didn't give it any throttle once I commanded second gear or the other gears. I only gave it throttle when I was in drive, and it wanted the trans in first.

Should I try and put it in drive, command second, then turn off the command for second, and see if it will shift with throttle?

Additionally, the trans shouldn't have any unusual programming going on to my knowledge, it was pulled from a stock 09' Escalade that had reverse issues.

This is now above my paygrade, not the kind of setup I ever work with. That being said, it never shifted past 2nd gear, it should have shifted no matter if you give it throttle or not since it showed it commanding it. But nothing happened looking at the OSS RPM, so something there does not add up. Then you have this weird command for PCS1 that should normally give you a solid bind in 4-5-6 but, nope the transmission just stays in 2nd. To top it all, you have a P0776 in memory which has to do with PCS2 not doing its job, but it is not involved in first gear so that sure is odd.... If the transmission was rebuilt then my guess is that you have a problem at the clutch select valve (backwards, missing end plugs or stuck) but if it has not been touched then it is some sort of command issue.

[08ColoRADo]

Trans was rebuilt. So there's a strong chance that there is something wrong internally. I appreciate your assistance on things to look for.

It definitely seems like it's not shifting out of 2nd gear, regardless of what I command it to do.

I'm going to keep reading through as much as possible to determine what it could be, but I'm also going to pull the trans sometime in the next few weeks and see if anything looks off internally. I'd hate to have to order a new reman unit after dumping money into rebuilding this one, but that's the road we're approaching. I can handle axle rebuilds, engine mods, transfer case builds, and fabrication galore. But transmission stuff escapes me.

[TransGo Robert]

It is most likely going to be in the valve body, just take it out and apart and you should be able to figure out what was done wrong. I can send you nice clear pictures that shows where everything goes. I see no need to pull the whole transmission at this time.