[FrankieSixxxgun]

Once the car gets hot, if I'm going about 50mph it'll begin to shift in an out of lockup. Fresh fluid in the tranny and a new lockup solenoid, so should I be looking at the TPS voltage or something? It's kind of annoying when it does it 4 times in a row, you know?

 

[Katshot]

Are you varying the throttle at all? It's quite common for people that tend to get on and off the throttle while trying to maintain a constant speed, to cause the VCC to go on and off.

 

[carnut]

Also verify that the TV cable coming from the trans to the throttle is ajusted to spec. If adjusted too long, trans will shift too early and soft, too short late and harsher. Lock up will be affected because of this. Any trans shop can adjust this to spec in about 15 min. if you dont have the factory service manual.

 

[N0DIH]

carnut is right, adjust the TV cable. And Katshot is right also, the TPS has a huge impact on TCC lockup speeds, so some throttle variance can have an effect.. My rule is readjust TV cable every 6 months. TPS typically only if messed with. I like to measure voltage on it at the ECM, not under the hood, as the TPS should be adjusted as the ECM "sees" it.

Also, take careful note when it unlocks, if you apply throttle slightly, does it lock up again? And then if you backoff throttle slightly back to maintain speed, does it unlock again? I had this problem, and TPS adjust and TV cable didn't affect anything.

I had an "OI" code THM200C, it ended up being an oil pressure switch inside the trans that told the ECM that the trans was NOT in 1st or 2nd. Only 2.14 geared cars and 2.41 geared cars had this "feature". I don't know the THM200 4R that well, but the 2 trans are related. It took me some time studying the FSM and the trans electrical diagrams when I figured it out. Of course, the "fix" was simply to cut the wire, allowing the ECM input to float high (logic high, typically from a 10K to 100K pullup resistor), which told the ECM it was in NOT 1st or 2nd all the time, as there is a 3rd gear ON switch, this is somewhat redundant, and posed no issues whatsoever.

So if you have the book, specifically look at your trans code (if there are any different diagrams for it) and see what else might be causing it if the TV cable adj and TPS adj doesn't cut it.

 

[the APEMAN]

The 2004R has a 4th gear pressure switch. Looks like an oil idiot light presure sender. That is another thing to check. Also the weatherpack 4 pin copnnector on the trans itself could be a problem.

 

[N0DIH]

Yup, that is exactly what the one in the THM200C "OI" code trans looked like. In the trans w/o, the port was just cast plugged.

If it works like the THM200C trans, likely disconnecting will work, but could possibly lead the TCC engagement in 3rd gear, providing a rough 3-4 shift if TCC is engaged. Else, no issues.

 

[FrankieSixxxgun]

When I was in there to replace the lockup solenoid and the tranny juice, the pressure switch looked okay. I checked the wires and they seemed good. I'm gonna chalk it up to the cable to the carb, because that thing is loose like spaghetti. I have the service manual, so I'll read up on it and pop and adjustment on it.

 

[FrankieSixxxgun]

Alright, so I checked the TV cable and it clicked right back into the same notch it was in, so it must be okay. The thing has a fairly new lockup solenoid, so it's more than likely the pressure switch, huh?

 

[N0DIH]

Can you disconnect the pressure switch wire? I honestly just cut the wire at the ECM and left it hanging. The ECM has a pullup resistor so it would float in a controlled state when the pressure switch was open.

Easier to patch a wire than to drop the pan and disconnect the sensor wire in my book.

Just watch for TCC Engaging at different times, but at least in my THM200C (3sp) it was never an issue.

 

[FrankieSixxxgun]

So you're saying cut the one wire to the pressure switch but leave the lockup solenoid wired? Would this make it enter lockup like a normal car or would this keep me out of lockup all together?

 

[N0DIH]

Exactly. The pressure switch (look at the schematics if you have them) is a confirmation to the ECM that you are not in 1st or 2nd. Then pressure to that port goes high from 3rd and 4th and the switch opens (normally closed or grounded). So in theory, the ECM could allow lockup on the TCC in 2nd if conditions were right. I never found it to ever do it in my 3speed car. I had 2.14 gears too.

So you're saying cut the one wire to the pressure switch but leave the lockup solenoid wired? Would this make it enter lockup like a normal car or would this keep me out of lockup all together?

I cut it at the ECM, as I didn't want to risk any bare wires under the car, and I had my ECM out (easy to get to on the Cutlass) and snipped it. Ran fine after that.

Again, my condition was directly related to that switch, as my trans go older the pressure was lower, and the 3rd gear pressure switch didn't have enough to allow it to operate properly. Mine would lockup under slight application of throttle more than cruise, and unlock at cruise. Annoying and hurt mileage. TV cable adjust didn't help, TPS was dead on, so I figured the tired THM200C (200K+ miles) just lost pressure.

 

[FrankieSixxxgun]

Sounds like it's about right. I'm going to re-verify that my TPS is on although I set it not too long ago and then I'll probably try disconnecting that connection. My tranny does the same thing, it'll jump into lockup when cruising up to speed, but if I hang out on the highway or interstate at 45-65mph, it'll randomly jump out of lockup, then back in, then back out, then back in. It's a pain in my ass and definitely kills my mileage. The tranny is about to have 198k on it, so it might just be old and tired too. Maybe next time I do the fluid I'll stick a new pressure switch in it, but for now, I'll just disconnect the wire to the thing.

 

[N0DIH]

that sounds like it. more load, it locks up, less load (cruise), it unlocks, but at a point where I knew it should be locked. Drove me batty!

Sounds like it's about right. I'm going to re-verify that my TPS is on although I set it not too long ago and then I'll probably try disconnecting that connection. My tranny does the same thing, it'll jump into lockup when cruising up to speed, but if I hang out on the highway or interstate at 45-65mph, it'll randomly jump out of lockup, then back in, then back out, then back in. It's a pain in my ass and definitely kills my mileage. The tranny is about to have 198k on it, so it might just be old and tired too. Maybe next time I do the fluid I'll stick a new pressure switch in it, but for now, I'll just disconnect the wire to the thing.

 

[FrankieSixxxgun]

that sounds like it. more load, it locks up, less load (cruise), it unlocks, but at a point where I knew it should be locked. Drove me batty!

Precisely! So, should I band-aid fix it by snipping the wire to override the pressure switch, or would replacing the pressure switch help? I don't mind dropping the pan and replacing the pressure switch if that's the right way to fix it, but if the tranny is just old and worn out, I guess there ain't much hope, huh?

This car shifted like a cloud for months after I got it and stuck a solenoid and some new fluid in the trans, but on the way to Atlanta a month ago, it started playing the lockup game with me.