pianoman

I have a 1994 1 ton Chevy Diesel 6.5 with a 4L80E 4X4 pickup (C3500)

Some one has replaced this transmission recently and it would not shift correctly. Scanner showed a problem with the output speed sensor circuit.

On visual inspection the input speed sensor and the vehicle speed sensor are hooked up, but the output speed sensor is not plugged in, no pigtail to plug it in.

I have opened up the taped up wire loom to find where many of the wires have been cut and respliced, but cannot find any empty wires that could lead to the output speed sensor. I thought someone may have simply not repaired them. I have followed the wiring harness up as far as the back of the engine, and still can't find any loose or cut wires.

Can someone tell me what color the wires to this sensor are supposed to be, or what terminals from the computer they use? Looks like I may have to go from the computer out with a new pair of wires.

Thanks for any help.

Roy D

jxaxsxoxn

iTrader: (2)

There should be two wires twisted together in there own conduit.
The rear speed sensor has a light gray with red stripe wire that goes to #9 on the computer.
The other wire is blue with white stripe and goes to #10 on the computer.

I ohmed my wires out all the way from the trans to the computer for identification.
It's been almost two years but I am looking at my notes and I have a '95 4L80E in the garage with the harnesses.
The colors are definatly right.
There is a blue/white wire in the harness that goes to the big plug, thats for something else. The two speed sensor wires are in there own conduits.

pianoman

I appreciate your help. They were probably in their own conduit at one time, but someone cut all the wires going to the transmission when they removed and replaced it. I'm the second person they brought this to because they couldn't make it shift. There are splices out the wazoo and tape everywhere. The only two wires I can't account for were the two for the out put speed sensor.

Just nothing spare left over like I expected to find when I opended up the harness, and my local Chevy dealer is not much help on wiring, nor was my manual.

I will get back under this truck tomorrow and look some more now that I know what to look for, but I think my best bet is going straight to the computer.

Again thanks, and I will give an update when I find the vanishing wires.

Roy

jxaxsxoxn

iTrader: (2)

I had a similiar situation because I bought my truck with no transmission, it originally had a 4L80E.
I know the wires for the two speed sensors are twisted around each other and the wires in the big conduit are just straight. The output speed sensor wires might be purple/white and light green/black. And they go to a vehicle speed sensor buffer which is a small white box under the dash, mine is behind the glove box.
I've always heard diesels have different transmission controllers.

pianoman

I'll keep that in mind this evening too.

Thanks

Rock-On

iTrader: (-2)

If memory serves me right the output speed sensor is in the transfer case ...the speed sensor in the rear of the tranny is mearly a dummie to plug the hole...I think if you look you'll see there is no exciter inside the tranny, Your sensor your looking for is in the transfer case itself. Got something to do with 4X4 low/high...hope this helps....Dave

pianoman

I wondered about that. I think you maybe correct about that, but on a two wheel drive the input and out put as well as the vehicle speed sensor are all used. But on this diesel 4x4 I can't find enough info here in my books to tell me. And I haven't found any spare wires anywhere. I did change the vehicle speed sensor (in the transfer case a while back due to eratic speedometer readings.) Also repaired one wire that had come out of it's splice for the input speed sensor. Going to try it out in a little bit and see if she shifts.

Thanks,

Roy

pianoman

Well, may have finally found the problem. While following the wirng harness back to the computer, I see where the harness goes down beside the turbo charger, and some of the wires have gotten hot against the turbo, looks like I have some splicing to do tomorrow. Now the speedometer is all over the place, and still no shifting. Think repairing the harness will repair it.

Thanks for your help, I'll let you know it's fixed.

Roy

Rock-On

iTrader: (-2)

I've checked the lot I've got three of them here.....none of them use the rear Output speed sensor, in the transmission....my teck tells me there are in the transfer case, just fyi...fix them wires and you'll fix this unit.