4R70W TC stays locked and stalls - TCCoA Forums
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post #1 of 3 (permalink) Old 11-19-2015, 06:51 AM Thread Starter
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4R70W TC stays locked and stalls

1998 4R70W.

I have a switch mounted on my floor that allows me to force the TC locked and an LED indicator light on my dash that tells me when it is locked either by the floor switch or the ECU.

Anyway, the other day I noticed the LED was flickering on and off and not when the TC was scheduled to lock. After a day or so it got progressively worse and I started to feel the TC locking when it shouldn't. Finally, it stayed locked and I found myself having to drop shift from neutral with some RPM to keep from stalling.

I had a P0743 so I started looking at the circuit. I removed my floor switch from the loop and the issue is still present. Pulled the pan and replaced the TCC solenoid and the wiring harness (ribbon) and cleaned the plug from the vehicle harness. Also swapped the ECU.

I still have lockup issues. Is there anything else other than replacing the TC? Should I be looking at the valve body?

My concern is I am not sure if the intermittent lockup indications are a result of a faulty electrical component or the reflection of the TCC position potentially commanded by a hydraulic malfunction.

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post #2 of 3 (permalink) Old 11-19-2015, 10:10 AM
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I would bet money that it is a wiring issue having to do with having a toggle switch installed. I know you said you removed it, but I would thoroughly check all the wiring, especially anywhere that you tapped into it. This is not a typical problem on the 4R70s, so I suspect that some wiring that you messed with is grounding out causing the converter to stay locked.

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post #3 of 3 (permalink) Old 11-20-2015, 04:20 PM
No, Mr. Lemmywinks, No!!!

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It should unlock in manual 1st or reverse; throwing the shifter all the way back should let it slip.

The TC cannot hydraulically lock in 1st gear, so if it does, the TC is wasted.

I have one that locks as soon as it comes out of first, so I know this problem.

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