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connerhistory

2015 silverado 6l80 transmission no forward or reverse

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Need help diagnosing my 6l80 trans. Truck has 120000 miles, trans fluid and filter were just changed about 1 month ago. 

 

I was driving the other day when my truck made some grinding noises coming off a stop sign and fell out of gear and would only rev. Managed to coast to a parking lot and cycled the key. Shifted into Drive and trans started making whining noise but went into gear however fell out as soon as I gave it some throttle, same in reverse and manual gears. Was able to load the truck up on a trailer by constantly starting and turning off engine and moving forward a few inches before falling out of gear. Got home and checked for codes, found codes (U0073 Can Bus A Off) (P2723 Clutch Pressure Solenoid E/5 stuck off) (C0800 Power Module issue) and (P0700 Generic trans problem code). Checked trans oil and it was dirty and burned with small metal flakes in it so I figured it was some internal issue like pump and clutches. Dropped the trans, opened it up and found a ton of metal dust and a few flakes in the pan. Tore into the clutch packs but none of the clutches were burned up or over worn, all be it a bit worn but not worn out. Pump had some wear on the bell housing but nothing emery cloth couldn't smooth out. Valve body seems normal and all the check balls are fine. No noticeable issues with seals or gears or valves. Did a resistance test on the Can Bus and it passed with 61ohms and the correct voltage readings. 

 

Im figuring the TCM/Solenoid Body because the Can Bus code, Solenoid E Off code and Power Code Along with Torque Converter because all the material in the pan and whining noise. Figured Id go ahead and replace the clutch plates and pump seals as well while I'm in there. 

 

Am I on the right track or could I be over looking something?

Are the new TCM units from the dealer plug and play or would it need to be flashed first?

Can these issues be explained by these components?

 

Thanks

Edited by connerhistory

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Mine was similar; it had a "servo boot" that tore if I recall correctly that caused 1st and reverse to stay engaged at the same time. After only a minute or two, I got your symptoms.

Edited by Shane T.

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Ended up fixing the issue,  Went ahead and replaced the TCM, Torque Converter, Pump Seals, and Cutch Pads since I had it opened.  Had a bad 3 to 4 shift flare after the new TCM was programmed but the adaptive learning figured it out after about 90 miles.  Works like new again. 

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On 7/19/2019 at 5:40 PM, Shane T. said:

Mine was similar; it had a "servo boot" that tore if I recall correctly that caused 1st and reverse to stay engaged at the same time. After only a minute or two, I got your symptoms.

 

On 7/31/2019 at 4:48 AM, connerhistory said:

Ended up fixing the issue,  Went ahead and replaced the TCM, Torque Converter, Pump Seals, and Cutch Pads since I had it opened.  Had a bad 3 to 4 shift flare after the new TCM was programmed but the adaptive learning figured it out after about 90 miles.  Works like new again. 

Shane T. Do you recall the boot that was torn? I believe I’m having the same problems, and I’m not much of a transmission guy.

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On 11/29/2019 at 3:59 PM, 2011Silverado said:

 

Shane T. Do you recall the boot that was torn? I believe I’m having the same problems, and I’m not much of a transmission guy.

6l80 transmissions are fully electronic/clutch-to-clutch operated. No servos, accumulator pistons, etc to worry about. Here's the manual I used... might help. Looking back the best course of action I should have taken, would have been to change the fluid and filter first and reset the tcm. 

http://shop.ukrtrans.biz/wp-content/uploads/catalogs/6L80.pdf 

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I appreciate the link. I was thinking more along the lines of the pressure switches leaking. Although, I may have an electrical problem instead. I installed a reman transmission and I will randomly have no forward or reverse after warm up.

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Checking into y’all post and want to run another 6l80 issue by everyone. Getting a U0073 and U0100 code. Gentlemen I’ve been talking through and helping me with this, we’ve been reading a lot of the high speed ends to make sure stuff is reading like it’s supposed to. My needles are bouncing. Truck is staying in a single gear. He thinks it’s the tehcm is bad. Any thoughts?

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3 minutes ago, sully94079 said:

Checking into y’all post and want to run another 6l80 issue by everyone. Getting a U0073 and U0100 code. Gentlemen I’ve been talking through and helping me with this, we’ve been reading a lot of the high speed ends to make sure stuff is reading like it’s supposed to. My needles are bouncing. Truck is staying in a single gear. He thinks it’s the tehcm is bad. Any thoughts?

That sounds like a "throw this part at it and hope the problem is fixed" style solution.

 

 It's more likely a wiring or connector problem, which sucks to find and is also relatively time consuming.  People don't want to pay for someone to careful unwrap/check/rewrap wiring harnesses, and test a bunch of connectors even if it is the most likely problem.  But if the mechanic quickly slaps in an expensive part and it doesn't fix the problem, you still have to pay for it, and you are more likely to accept the cost of checking the wiring harness, as it doesn't seem so bad then...

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2 minutes ago, davester said:

That sounds like a "throw this part at it and hope the problem is fixed" style solution.

 

 It's more likely a wiring or connector problem, which sucks to find and is also relatively time consuming.  People don't want to pay for someone to careful unwrap/check/rewrap wiring harnesses, and test a bunch of connectors even if it is the most likely problem.  But if the mechanic quickly slaps in an expensive part and it doesn't fix the problem, you still have to pay for it, and you are more likely to accept the cost of checking the wiring harness, as it doesn't seem so bad then...

Well I haven’t thrown any money at it yet. Really just ohming out the high speed side of stuff to hopefully find a broken connector or wire somewhere. Not really wanting to throw a tcm in it if it’s a broken wire

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I would suggest getting a subscription at a site like alldatadiy.com for the full-service manual for your truck, and reading through the diagnostic procedure for those codes, and work through them (course, likely part of them will involve hooking up an advanced code reader to perform some computer tests).

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Posted (edited)

the plastic check valve balls can deform and cause pressure loss, pull valve body inspect them and the separator plate, and inspect the wafer thin switches  on the Tecm. other than over heating the fuid, the 6l80 design is simple, but its the software that makes it so reliable, if a sensor, solenoid  or check valve go bad then software cant compensate for that or for bad seals that have been dried out and oxidized  due to heat,, 

Step #1 remove the inline thermostat in trans

 

if the plastic components inside look brown or dark black , this trans probably been overheated, the plastics inside should look either white or pink in color

Edited by flyingfool
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4 hours ago, flyingfool said:

the plastic check valve balls can deform and cause pressure loss, pull valve body inspect them and the separator plate, and inspect the wafer thin valves on the Tecm. other than over heating the fuid, the 6l80 design is simple, but its the software that makes it so reliable, if a sensor or check valve go bad then software cant compensate for that for bad seals that have been dried out and oxidized  due to heat,, 

Step #1 remove the inline thermostat in trans

 

if the plastic components inside look brown or dark black , this trans probably been overheated, the plastics inside should look either white or pink in color

Appreciate it! Plastics looked good when I changed the fluid. Truck has 88K on it. I’ll drop the pan again and see what it looks like. 

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check the solenoids

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