4L80 Slippage Issues

[Z06Luke]

I'm working on a 2003 2500HD that's experiencing high transmission temps and data logs seem to show slippage. This is not the type of issue I've done much troubleshooting of before, so I'm somewhat learning as I go here. The torque converter and lockup solenoid were both just replaced in attempt to solve this issue, and the transmission is beautifully clean inside, fwiw. Some spark advance tuning has been done, but no changes have been made to the transmission tuning.

I have a short log (slipping log.hpl) of freeway driving showing a constant 80% slippage, despite varying RPMs of slippage. A 2nd log (slipping log2.hpl) is attached showing more data, including times when slippage is basically 0 (1:59:12) and it still shows 80% of slippage. Tune file is also attached. Any help would be appreciated.

[kingtal0n]

You need to know how much pressure commanded and how much actual pressure in the transmission.

For commanded pressure you should LOG the "Force Motor current" It will be presented in mA of current (milliamps) where LOW current is a HIGH pressure.

For Actual pressure this requires a pressure gauge on the side of the transmission plugged into the pressure tap port on top of the trans (top/side) I think its 1/8" NPT

First you need to see if the pressure is being commanded enough to keep from slipping.
Then you need to see whether the trans is actually producing enough pressure in reality to keep from slipping, if it is actually being commanded.

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[TransGo Robert]

I'm working on a 2003 2500HD that's experiencing high transmission temps and data logs seem to show slippage. This is not the type of issue I've done much troubleshooting of before, so I'm somewhat learning as I go here. The torque converter and lockup solenoid were both just replaced in attempt to solve this issue, and the transmission is beautifully clean inside, fwiw. Some spark advance tuning has been done, but no changes have been made to the transmission tuning.

I have a short log (slipping log.hpl) of freeway driving showing a constant 80% slippage, despite varying RPMs of slippage. A 2nd log (slipping log2.hpl) is attached showing more data, including times when slippage is basically 0 (1:59:12) and it still shows 80% of slippage. Tune file is also attached. Any help would be appreciated.

You log is not super useful because it is missing the two most important PIDs. ISS/TSS and OSS. If course it would help also to have the Force Motor solenoid desired and actual amperage as well.

Ignore that TCC slip % that's a goofy misleading PID. focus on the TCC Slip RPM PID.

You have no lock-up apply at all from what I can see in there with the very limited number if transmission PIDs. When you see zero slip that's juts because you released the throttle so there is no load, you are actually coasting down at that point.

The number 1 reason for TCC slip in a 4L80E is a cracked lock up piston in the converter. It could also be the TCC regulator valve in the valve body but that usually does not cause it not lock at all like that, more of an excessive slip when the fluid gets hot and worse when you load it a bit. We have a drop in fix for that if you find that your valve body is worn. https://transgo.com/product-details/4l80-tcc-regulator/

[Z06Luke]

I got the issue figured out. I probed the TCC lockup wire at the transmission and confirmed that it was getting signal from the PCM. Replacing the valve body resolved the issue.

[TransGo Robert]

Glad you got it figured out and thanks for taking the time to post the fix.