2017 Tahoe 6L80 Transmission Issue

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JustinCole

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So I replaced the condenser on my wife’s Tahoe and was having major issues getting the transmission cooler line snapped in. I thought I had it in with snap ring on it and then the next day I drove it and only made it about 8 miles before the transmission started acting up with rpm’s jumping all over the place and vehicle not moving properly. I pulled over and seen trans fluid coming out from condenser. The trans cooler line blew out. Also when I turned the truck off the trans temp was only at 185. I had it towed back home and finally got the cooler line in properly and added trans fluid but now check engine light, ABS, BRAKE, and traction control lights are illuminated on the dash. The code that comes up is P0796 and the suv will not move forward or reverse. I don’t feel like I did catastrophic damage but what do I do next??
 

NickTransmissions

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So I replaced the condenser on my wife’s Tahoe and was having major issues getting the transmission cooler line snapped in. I thought I had it in with snap ring on it and then the next day I drove it and only made it about 8 miles before the transmission started acting up with rpm’s jumping all over the place and vehicle not moving properly. I pulled over and seen trans fluid coming out from condenser. The trans cooler line blew out. Also when I turned the truck off the trans temp was only at 185. I had it towed back home and finally got the cooler line in properly and added trans fluid but now check engine light, ABS, BRAKE, and traction control lights are illuminated on the dash. The code that comes up is P0796 and the suv will not move forward or reverse. I don’t feel like I did catastrophic damage but what do I do next??
Check fluid level, top off until it's at full when hot (160 degrees+) then try to drive it. If it still won't move, the following are causes:

1. Torque converter failure
2. Pump rotor/slide break up
3. Check ball #1 and #5 both stuck in plate or migrated away from their seating locations
4. Input shaft splines stripped
5. Transfer case failure (if a 4WD)

P0796 is a solenoid code for clutch pressure control solenoid #5, which monitors the performance of the CBR1/4-5-6 clutch boost and regulator valves in the upper valve body. It's telling you that either the TEHCM itself is bad or the CBR1/4-5-6 valve train is impaired in some way (usually means the bore plug is leaking, resulting in poor response to solenoid signal oil under commands issued by the TEHCM).
 

tom3

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First thing I'd do is unhook the battery for a couple hours, hit the brakes to have the lights totally bleed the circuits. See what happens when restarted and idled for a few minutes. Sees to fix a lot of issues in these machines.
 

NickTransmissions

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First thing I'd do is unhook the battery for a couple hours, hit the brakes to have the lights totally bleed the circuits. See what happens when restarted and idled for a few minutes. Sees to fix a lot of issues in these machines.
It does, except for the transmissions...I'm thinking he simply didn't put enough fluid in it - perhaps a couple quarts (2-3) low which would generate a no-movement condition in many cases. At least, that would be the simplest and preferred cause here...Everything else means extensive diag work which me may or may not have the appetite for, at least as DYI...
 
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JustinCole

JustinCole

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It does, except for the transmissions...I'm thinking he simply didn't put enough fluid in it - perhaps a couple quarts (2-3) low which would generate a no-movement condition in many cases. At least, that would be the simplest and preferred cause here...Everything else means extensive diag work which me may or may not have the appetite for, at least as DYI...
Ok yes I have added some fluid but not at 160+ operating temp. I will definitely try that first. Would it do some good to go ahead and drop the pan and replace the filter as well? I watched your video on diagnosing the solenoids with volt meter but I’m to the point where I’m willing to just buy a whole new TEHCM and replace it if the fluid level isn’t the fix. Wouldn’t that take care of the solenoids and valve body all at the same time? I have a 2016 Silverado as well that I have replaced torque converter in and also condenser. I will say GM dropped the ball on those two components in these year models.
 
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NickTransmissions

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Ok yes I have added some fluid but not at 160+ operating temp. I will definitely try that first. Would it do some good to go ahead and drop the pan and replace the filter as well? I watched your video on diagnosing the solenoids with volt meter but I’m to the point where I’m willing to just buy a whole new control module and replace it if the fluid level isn’t the fix. I have a 2016 Silverado as well that I have replaced torque converter in and also condenser. I will say GM dropped the ball on those two components in these year models.
Yea, check it when hot so you have an accurate reading on where the level is at relative to where it needs to be...Hopefully that's it...If you're full-hot and still no movement, do a line pressure test to confirm/deny the pump is making pressure. The line pressure port plug is located on the driver side of the unit, just behind the bell housing and needs a 7/16" socket to remove...Once out, just thread in your transmission pressure gauge, fire up the vehicle and see what your readings are in P, R, N, D, M....If the pressure readings are zero, it will need to come out...

If you have normal pressures at idle in P, R, N, D, M then drop the pan and see if there's kibbles and bits, burnt clutch material, etc...Then ohm out the solenoids per that video and see if you come up with anything...There is one caveat when it comes to DVOM testing solenoids: They can test good electrically but fail mechanically...The six-speeds and later transmissions are usually sensitive/sophisticated enough to alert you via DTC if a variable force solenoid has failed, regardless of failure mode (elec vs mech) but not 100% of the time. Lastly check your pressure switches...They work with the IMS to constantly communicate range position to the TEHCM's leed frame and PCM so if certain ones go bad, you won't have movement at all...

The main takeaway here is to ensure you've confirmed the TEHCM is no good (and that your symptoms don't have their source in the valve body and/or main case) before spending $$$ on a new one. You will need Snap On 10EPL socket (E Torx 12) to remove the 6 TEHCM/VB to case bolts holding everything to the bottom of the case.
 
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JustinCole

JustinCole

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Thanks I agree. I’ll try fluid level first and go from there. I will update my findings.
 

MikeK1981

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Thanks I agree. I’ll try fluid level first and go from there. I will update my findings.
Don't feel too bad, the dealer did the same thing to ours after a condenser replacement. Made it a few days and the line popped off. Made a huge mess under the hood and went completely into neutral. Had to get towed back and fixed again.
 
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JustinCole

JustinCole

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Update: I did a filter change and put new fluid in to the correct levels while running at operating temp and all lights went off and now drives. Been driving it for a couple of days and everything seems to be working properly. I have been checking fluid levels daily with no issues. Thanks for the help.
 
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JustinCole

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Update Update::: So this might be the wrong thread for this but if anyone has some insight please share. From the beginning, replaced condenser, trans cooler line blew and replaced fluid and filter, finally got it back on the road and been driving for a couple of days and now the front a/c works fine but the rear a/c is blowing hot air only. Checked refrigerant and levels are good. Could this be from a fuse that got blown during all the previous processes or is this leaning more towards the rear door actuator? Funny enough I can’t find anything online about replacing rear door actuator on anything 2016 or newer. I’m literally about to drive this thing off a cliff…jk
 

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