Odd 4L80E TCC Problem
Thread Starter
TECH Fanatic
Joined: Jul 2010
Posts: 1,756
Likes: 4
From: Maryland
Odd 4L80E TCC Problem I purchased an '01 Suburban 6.0 2500 4x4 basically for use on long trips, light trailering, and winter use, etc and has been well taken care of and pulled a single horse trailer from time to time in it's prior life.
My issue is with the trans TCC...up to 50-65 MPH it will slide in/out of lockup as designed with no issue at all. On the highway, one I hit 72 MPH it drops out of lockup and does not re-engage until speed falls to 50 MPH or below. This happens like clock work, right at 72 MPH. Also, if I am cruising at 68-70 and I take my foot off the gas, it will unlock (as it's supposed to) but again will not lockup until speed drops to 50 MPH.
If I never go over 65 MPH, it will slip in/out of TCC as designed...and never have an issue. Once you get out on a long road trip, no way in hell you can stay at 65 lol.
I have HP Tuners and see nothing in the tune that would cause this. I disabled the P0300 DTC just in case, ensure the brake pedal is adjusted correctly, and nothing changes. I even went so far as to program the trans cal to stay in lockup when the TPS is at 0% down to 40 MPH...nothing, same problem. It still drops out of lockup despite being tuned otherwise and functions exactly as it did prior to tuning.
Only thing I can think is to do a "write entire", but that should not be required. Also, the TCC cannot be commanded via the scan function for some reason.
The trans operates very well otherwise, no issues at all. Fluid is clean, no shudders, no DTC's, nothing. Completely at a loss here.
My issue is with the trans TCC...up to 50-65 MPH it will slide in/out of lockup as designed with no issue at all. On the highway, one I hit 72 MPH it drops out of lockup and does not re-engage until speed falls to 50 MPH or below. This happens like clock work, right at 72 MPH. Also, if I am cruising at 68-70 and I take my foot off the gas, it will unlock (as it's supposed to) but again will not lockup until speed drops to 50 MPH.
If I never go over 65 MPH, it will slip in/out of TCC as designed...and never have an issue. Once you get out on a long road trip, no way in hell you can stay at 65 lol.
I have HP Tuners and see nothing in the tune that would cause this. I disabled the P0300 DTC just in case, ensure the brake pedal is adjusted correctly, and nothing changes. I even went so far as to program the trans cal to stay in lockup when the TPS is at 0% down to 40 MPH...nothing, same problem. It still drops out of lockup despite being tuned otherwise and functions exactly as it did prior to tuning.
Only thing I can think is to do a "write entire", but that should not be required. Also, the TCC cannot be commanded via the scan function for some reason.
The trans operates very well otherwise, no issues at all. Fluid is clean, no shudders, no DTC's, nothing. Completely at a loss here.
Thread Starter
TECH Fanatic
Joined: Jul 2010
Posts: 1,756
Likes: 4
From: Maryland
I found a partial solution to this problem...apparently the EGR was bad, I disabled the EGR and the TCC resumed "normal" operation. The HP Tuners was not able to modify the trans tune for some reason, even after completing a "write entire". The commands in the scanner are still inoperative, also. I guess I'll have to write HP Tuners and tell them their **** doesn't work.
