TCC erratic release commanded by PCM

[ttls1]

Hi, I have a problem that has just shown up today and I am about 2500ks from home and hoping to be able to sort it. The converter lock on my 4l80e is releasing for no reason I can identify. I have logged the TCC mode pid and the PCM is actually commanding the release. I will unlock for a couple of seconds and then lock back up. Sometimes it will only happen every 5 mins and sometimes it will constantly lock and release. I have no DTC's current and speeds and TP are all well within the locked window. The only thing I have noticed is the VSS will drop 10klms for a split second every few mins but not when the unlocking is occurring so I don't think it is related. Unfortunately I am not in a place where I can get parts. If someone could let me know what could cause a commanded unlock that would be great. It will give me something to log and try to narrow down. The engine is a Lq4 and appears to be running fine with no misfires. I have a trans temp and pressure gauge and all appears fine. The trans level is good and I just replaces the oil 1 week ago.

Any info will be greatly appreciated

[joecar]

Log the TSTATEnn pids, these may show the reason for unlocking the TCC.

Sounds like you VSS connector needs to be wiggled.

[Supercharged111]

Or a wonky brake switch? Try lifting up on the brake pedal when it unlocks and see if it doesn't lock right back up.

[joecar]

Good idea about the brake pedal switch... one of the TSTATE pids has a bit flag to indicate state of brake pedal switch.

[ttls1]

Thanks for the info everyone. I logged the TSTATE pids and found out that the tcc was being commanded an unlock due to a downshift. I did a lot more logging and noticed that the vss was actually the cause. I was able to get a replacement vss but this did not fix the issue. I had to cut the plug off the vss and run a temporary cable to the PCM. This fixed the issue so it would appear I have a break in one of the wires as they meter out ok but must open circuit intermittently. Anyway I got home no probs. Cheers