Please Help diagnose why TCC will not lock up

[zigm]

Car has a 2800 stall vigilante LU converter...

Troubleshooting efforts so far:
- Manual shorting of top outer pins on ALDL definitely locks TCC. (clutches feel pretty good, solenoid seems fine)
- Purple wire on transmission side harness has 12V with ignition 'on'. 12V goes away when brake pedal is pressed.
- Brake switch appears to be adjusted correctly.
- Turbometer ALDL scan log shows vehicle speed feedback is pretty accurate, 3/4 gear indicators working, and TCC locking up at low load cruise.

But, the TCC just will not lock without jumping the ALDL manually.


Any ideas? It seems the signal from the ECM is not getting to the transmission. (loose wire somewhere?)

Thanks,
William

 

[mikestertwo]

If your scan tool is showing the converter lock signal then either the computer driver is bad or you have a bad connection at the computer pin "A7". Check continuity between "F" on the ALDL connector and "A7" on the computer connector. If it is good check for corrosion on the computer pin. If all looks good replace the computer.

 

[Alky V6]

A last ditch test before replacing that computer will be to back probe the TCC command line (TCC solenoid ground) at the computer with your digital volt/ohm meter while running. Foot off the brake. When the computer is not commanding L/U (use scanner), you will have 12V on that line. When the computer commands L/U the line will go low or 0V. If you find you don't have 12V with a back probe of the computer, trace down the circuit to find out why.

 

[zigm]

Performed a bit more troubleshooting tonight...

With connector still hooked up to ECM:
- Tan/Black wire @ ECM (A7) has continuity to F on ALDL
- A7 has 12V when ignition on. 12V with engine running. 12V goes away when brake pedal is pressed.
- Hooked up a test light to A7 & went for a drive. Light only went out when I pressed the brake. Logger showed TCC lockup, but light stayed on. (TCC would lock when light was attached - I'm guessing it raised the resistance enough)

Sounds like my ECM driver is bad! (?)
Is there a repair for this, or is it time to look for another ECM?

Thanks again,
William

 

[mikestertwo]

Just replace the ECM. They are redily available.

 

[zigm]

Thanks for the help guys.
Bought a used ECM off the board and installed it yesterday... TCC locks up just fine now!

Problem solved. :smile: