jpyy85

Hi everyone. I have a 1988 Pontiac Trans AM GTA with the 350 TPI and the TH700-transmission. I would be grateful for some help with my TCC, because I have no lockup in the car.

Transmission shifts fine through all the gears in both OD and regular D but there is no lockup occuring. And slightly touching the brakes when crusing on the highway does nothing to the RPMs.

I have searched a lot about this problem and if I understand correctly first step is to check with a test light in the ALDL between terminals A and F with the ignition on. It should light up and then go out when pressing the brake. Mine does neither. Doesn't light up the testlight and pressing the brake does nothing.

Voltmeter on the other hand, gave a reading of about 11,6 volts. (with the ignition on). Pressing the brake doesn't really affect the reading, it drops a few decimals, propably because of the brake lights illuminating but nothing else happens.
Cruise control works fine and turns off when touching the brake, so brake switch seems fine?

The connector at the transmission also had similar readings when I measured it with the voltmeter, but again pressing the brake does nothing.

Am I doing something wrong here? Because since there is voltage shouldn't the TCC always be locked, if pressing the brake does nothing?

Any recommendations for what the next steps should be?

T.L.

The lock-up solenoid in the transmission could be bad. I had to replace mine...

formularpm

I don't think so. The switch could be stuck open.

You could check for power at the solenoid with a test light or meter with the brake not depressed. That would rule out the switch.

If so, it could the solenoid itself or connection on the ground side.

jpyy85

I am leaning towards just buying a new solenoid at this moment, and hopefully it will fix it, they are so cheap anyway. Since brake lights work and cruise control shuts off when applying the brakes, it should be the solenoid, right?

T.L.

Yeah, the solenoid is cheap but ATF is expensive these days (LOL !!!)...

jpyy85

Especially since I replaced the ATF-fluid less than two months ago, lol.


I just ordered a new solenoid, I will return and post an update after I have received and installed it.

MadelineScott

Any update?

jpyy85

Not yet, we have got two small kids at home and the car is my project car, so time is a luxury. lol

Hopefully will get it done this week though. I've got the spare part and fresh fluid waiting.

jpyy85

So, finally found the time and replaced the solenoid which looked original. And now it blows the gauges fuse immediately when turning on the ignition. The same fuse that also handles, of course, the TCC solenoid. It didn't do this before.

What do you guys suggest I do next?

Update:
I think I found the answer here on some Buick Forums.

"Either you have a wire shorted to ground, a bad solenoid (internal short), or the solenoid is wired backwards"
https://turbobuick.com/threads/tcc-r...-blows.448858/

Well, I guess I'll have another ATF-bath during the weekend.

jpyy85

Alright, so I finally pulled the pan yesterday and the wires from the solenoid had gotten pinched between the pan. Some new tape on the wires and reassembled and I finally have lockup.

The old solenoid did have a faint "pop" when giving it 12v straight from the battery, but nowhere like the new one. And the old one didn't rattle when shaken, like the new one did. So maybe it was stuck or something.

​​​​​Enough of the ATF baths for a while hopefully. I bought a 12v oil pump for the second time I pulled the pan. Much easier and cleaner to suck out most of the oil through the dipstick before removing the pan.
​​​​​

T.L.

Glad you got it figured out...