4L80 limp mode no codes

[lpowell3453]

I was getting code 71, 81, and 82. I replaced engine speed sensor, internal transmission wiring harness, 1-2 and 2-3 shift solenoid. Then noticed burned wiring harness close to transmission connector. Fixed burned wires now shifts normal for first 3 or 4 miles then limp mode. If I turn engine off and restart it will shift normal again but only for about a mile then limping again. TCM has no codes when I jump A and E.

 

[Mogman]

Welcome to the forum!
Are you still getting a trans light when you first switch on the ign.? will it go a mile at a time every time you restart, or does it get shorter each time?

 

[NDT]

Is all your transmission wiring in and behind the battery box in perfect shape? To include the relay?

 

[lpowell3453]

Welcome to the forum!
Are you still getting a trans light when you first switch on the ign.? will it go a mile at a time every time you restart, or does it get shorter each time?

Yes light with ign on engine off. I haven't drive far enough to know of it gets shorter each time. I do also now have a battery going bad could this be related to that? It will be replaced next week.

 

[lpowell3453]

Is all your transmission wiring in and behind the battery box in perfect shape? To include the relay?

This is an '87 m998 that had the 6.2, 3 speed. I transplanted a 6.5t, 4 speed about for years ago. It has worked great until the harness shorted out about 3 weeks ago. It doesn't have the normal wiring with the relay. But I checked the wiring I did and I think it is good.

 

[lpowell3453]

This is an '87 m998 that had the 6.2, 3 speed. I transplanted a 6.5t, 4 speed about for years ago. It has worked great until the harness shorted out about 3 weeks ago. It doesn't have the normal wiring with the relay. But I checked the wiring I did and I think it is good.

 

[lpowell3453]

I think i have found the problem. I opened up the tcm so i can see the cir uit board

 

[lpowell3453]

I think i have found the problem. I opened up the tcm so i can see the cir uit board

Sorry trying to do this on my phone. The circuit board has a blown varistor. It has burnt to numbers off iy. Does anyone have a picture of the circuit board that i can read the varistor numbers from? The varistor is the brown nickel sized part oin the picture.

 

[Mogman]

A varistor is a surge protection device, unless it is shorted the circuit should work, if it is shorted cutting one lead should make the circuit work, but if the issue causing the surge is still there it will fry.
Most likely if the surge was strong enough to blow the varistor the circuit is already toast, I have seen dozens of these blown on other applications and other components have always been damaged, to say if they are blown they failed to protect the device.
I am surprised they used a varistor for low voltage protection, a zener diode would have been a much better choice.
There are several used TCMs on fleabay search for 16147609
I have a good tested TCM but under the circumstances I could not guarantee it.

 

[lpowell3453]

A varistor is a surge protection device, unless it is shorted the circuit should work, if it is shorted cutting one lead should make the circuit work, but if the issue causing the surge is still there it will fry.
Most likely if the surge was strong enough to blow the varistor the circuit is already toast, I have seen dozens of these blown on other applications and other components have always been damaged, to say if they are blown they failed to protect the device.
I am surprised they used a varistor for low voltage protection, a zener diode would have been a much better choice.
There are several used TCMs on fleabay search for 16147609
I have a good tested TCM but under the circumstances I could not guarantee it.

I think the shorted and burned wiring harness is what caused this damage. It is now fixed so I think I am good there.