4t60 - TCC Problem

[paulo57509]

The TCC in my '92 Lumina will occasionally disengage at a constant cruise speed, such as 60mph on flat terrain. It disengaes and then will re-apply after 15 seconds or so. It doesn't do this very often. It will do this once in about 15-20 miles or so.

It started doing this a few days ago. I serviced the filter and fluid yesterday but this didn't help. The fluid isn't burnt and the transmission shifts fine.

I'm thinking it's more of an electrical problem than a hydraulic one. Perhaps I'm losing the TPS or VSS signal momentarily, or the brake switch is faulty.

My next attempt at a diagnosis is to connect my scan tool to see if I can get a VSS or TPS reading when the clutch disengages.

Any other thoughts or comments would be welcomed. BTW, the transmission is original to the car and has ~134k miles on it. It's never given me any problems in the past.

TIA

[sharkey]

when you get the scanner on it, watch to see if the computer is comanding lockup to be off when it comes out. if the scanner says lockup: off, then its an input problem and the transmission is fine. if the scanner is commanding lockup on, then you have either a brake switch problem, wiring, solonoid, or transmission problem.

if the computer is commanding it off, check your vss, tps and map.

[paulo57509]

Sharkey, Thanks a lot for the reply. I'll have a chance later in the week to do some troubleshooting. I'll post up what I find. Thanks again.

[Rhedalert]

The brake lamp switch also acts as a TCC cutoff. Next time this seems like it will happen, lift up on the brake pedal from behind and see if that lets it re-apply.

[paulo57509]

The brake lamp switch also acts as a TCC cutoff. Next time this seems like it will happen, lift up on the brake pedal from behind and see if that lets it re-apply.

Brian, this was the first thing I tried. No dice. I have yet to crawl under the dash to put the eye ball on it, but it's on the to-do list.

[paulo57509]

I don't know what happened, but it appears to have corrected itself. I don't believe that the problem is gone for good, but I hooked up the scan tool and drove drove approximately 160 miles over the same conditions (the same road, in fact) where the problem had occurred in the past. It didn't act up once.

I guess it's the wait and see approach now.

[paulo57509]

Just to close the loop on this thread, I believe I might he found the problem.

The past week, the engine developed an intermittent miss. It progressively got worse as the days went by until the intermittent became quite steady.

After checking for vacuum leaks, I traced the problem to a bad plug wire (#5 cylinder). After replacing all the wires (they were originals) the miss is gone.

My theory is that the engine would lose a cylinder and because the cruise control was engaged, would open the throttle to compensate. This would unlock TCC momentarily until the set speed was regained and the TCC would lock again.

Again, I'll just wait and see.