6L80 Goes into false neutral

Drivetrain discussion including Transmission, Differential, Driveshaft, and related items.
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Holdendeeznuts
Posts: 5
Joined: Fri Dec 17, 2021 6:36 pm

6L80 Goes into false neutral

Post by Holdendeeznuts »

Hello,
I recently purchased a 2011 caprice ppv from the bay area CA. When I drive the car like a grandma (staying under 2500 rpm) it shifts through all the gears, no slipping, drives completely fine. You would be able to tell there is anything wrong with the car. HOWEVER once you mash your right foot into the ground, the car will try to down shift and rev out as if you are in neutral. Kinda feels like you missed a gear, or hit a false neutral on a motorcycle. Eventually the car will go into limp mode after doing this a few times and then it will only hold 3rd gear.

SO I scan the car and find 2 codes. U0073 (control module communication bus "A" off) and P0700 (transmission control system malfunction) which I believe is a very generic code for the TCM.

Based off this I hope that it is a solenoid or the TCM itself? My fear is that the clutches are fried and the trans needs a rebuild. I have yet to pull off the oil pan, but plan to after the holidays, just a bit busy right now.

If anyone has dealt with this before any input is appreciated.
Reno/Tahoe, NV
2011 Caprice
2018 Toyota Tacoma Turd offroad
1978 yamaha xs750
2021 yamaha YZ250
cerbomark
Posts: 316
Joined: Tue Oct 02, 2018 5:37 pm
Location: upstate NY

Re: 6L80 Goes into false neutral

Post by cerbomark »

first thing is make sure fluid level is correct.
2016 C1
andrewquant
Posts: 38
Joined: Fri May 28, 2021 2:47 pm

Re: 6L80 Goes into false neutral

Post by andrewquant »

Are you able to data log the pressures for the PCS Sol 1-5? If so, give us a datagram. Also include trans slip rpm and torque converter slip rpm. Need to see if the slip is trans or TC. Check the fluid level first, but there is a good chance you may have a leak in the trans or pump. That can be verified with a mechanical gauge on the test port and a tech2 to command pressure. Try and see which gears it slips in. Each gear (except 1st and R) uses two clutches. So if you can figure out what gears it always does it in, or never does it in, we can isolate it to one clutch. The clutches are 1-2-3-4, 3-5-R, 2-6, and 4-5-6. If you bash it from a stoplight and 1st gear holds, they your line pressure and your 1-2-3-4 clutch are prob ok. You can cross that one off.
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smwalker
Administration Staff
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Joined: Mon Jul 29, 2013 1:44 am
Location: Azusa,CA

Re: 6L80 Goes into false neutral

Post by smwalker »

common problem is the #1 check ball get small and get jammed in the plate holes.
See this vid for an example. quite interesting.

https://www.youtube.com/watch?v=HSvWikVP-4M
Steve Walker
Azusa, CA
'11 PPV 9C3 Huron White
GammaFlat
Posts: 259
Joined: Mon Sep 21, 2020 9:26 am
Location: NW Indiana

Re: 6L80 Goes into false neutral

Post by GammaFlat »

It is surprising that the check ball is not steel?! Also surprising that the ball shrunk so much. Is that plastic? Nylon?
Current: 2013 9C3, deeper trans pan, 12VoltSolutions Remote, Class III hitch, Android Auto capable radio
Holdendeeznuts
Posts: 5
Joined: Fri Dec 17, 2021 6:36 pm

Re: 6L80 Goes into false neutral

Post by Holdendeeznuts »

A lot of knowledgeable feedback. Thanks. Going to try to work on this thing over the weekend….after I dig the car out of 3ft of snow :)
Reno/Tahoe, NV
2011 Caprice
2018 Toyota Tacoma Turd offroad
1978 yamaha xs750
2021 yamaha YZ250
Holdendeeznuts
Posts: 5
Joined: Fri Dec 17, 2021 6:36 pm

Re: 6L80 Goes into false neutral

Post by Holdendeeznuts »

UPDATE: trans fluid was a bit low. Topped it off, car still has the issue. Going to drain the oil and look at the valve body. Might be the check ball.
Reno/Tahoe, NV
2011 Caprice
2018 Toyota Tacoma Turd offroad
1978 yamaha xs750
2021 yamaha YZ250
Holdendeeznuts
Posts: 5
Joined: Fri Dec 17, 2021 6:36 pm

Re: 6L80 Goes into false neutral

Post by Holdendeeznuts »

UPDATE: dropped the pan. Not much debris in there. Assuming clutches are good.

Took valve body off. Split it. Looked at the check balls. They are all where they are supposed to be. Going to check solenoids on the TECHM next. Beginning to think the TCM is the issue. Not 100% sure at this time.
Reno/Tahoe, NV
2011 Caprice
2018 Toyota Tacoma Turd offroad
1978 yamaha xs750
2021 yamaha YZ250
smwalker
Administration Staff
Posts: 2201
Joined: Mon Jul 29, 2013 1:44 am
Location: Azusa,CA

Re: 6L80 Goes into false neutral

Post by smwalker »

While you got it apart consider the deeper pan and larger mouth filter modification. It supposedly fixes the flare problem but I have never hear of the flare problem causing a limp mode situation. Why I initially thought he check ball might be your problem.

Deep Pan Mod:
https://www.newcaprice.com/forum/viewto ... =821#p7418
Steve Walker
Azusa, CA
'11 PPV 9C3 Huron White
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