OD all of the time

[mmiller54sc]

I have a 1991 explorer 4wd. I cannot seem to take off in OD. I have all other gears and they shift fine. When I put it in OD, it feels as if it goes into gear and moves slightly. I think I have it narrowed down to the TCC solenoid. I seem to be getting a ground signal to both solenoid wires as soon as I crank it up. Could it be getting false signals from the PCM or is this normal?

 

[MrShorty]

A fault in the TCC solenoid circuit would only effect the torque converter lockup clutch, which would only be noticeable above ~40 mph. If the truck isn't going or is just barely going in the OD position (indicating something slipping or not fully engaging) this won't be caused by a bad TCC or 3-4 shift solenoid.

 

[mmiller54sc]

If either of the solenoids were getting a signal early, would this cause the OD valves to be open all of the time. Not just when it was supposed to over 40 mph. I am getting ground to both solenoids all of the time. Isn't this what causes them to energize?

 

[PopRichie77]

How are you checking for grounds? The PCM is connected to the negative side of the solenoids. If the TC solenoid was shorted to ground it would lock up as soon as the engine was turned on and would stall the engine as soon as you put it in gear.

 

[MrShorty]

If the TC solenoid was shorted to ground it would lock up as soon as the engine was turned on and would stall the engine as soon as you put it in gear.

Not necessarily. My own experience suggests that the TCC lockup (and 3-4 shift, I believe) are hydraulically inhibited in the valve body to prevent just the scenario you describe. If the 3-4 shift and TCC solenoids have a constant ground to it, I would expect it to drive just fine until it shifts into 3rd gear, at which point it would immediately shift into 4-locked and stay there until it shifts back into 2nd.

 

[PopRichie77]

The test to see if the Torque Converter will lock up is just as I described.

 

[mmiller54sc]

I unplugged the plug from the transmission that goes to both solenoids and checked from the red hot wire to each of the other 2 wires. I get a reading when I do this on both wires. Correct me if I am wrong, but the red wire is the common hot for both solenoids and the other wires are the signal grounds coming from the PCM. I believe one is orange and yellow and the other is purple and yellow.

 

[imp]

I unplugged the plug from the transmission that goes to both solenoids and checked from the red hot wire to each of the other 2 wires. I get a reading when I do this on both wires. Correct me if I am wrong, but the red wire is the common hot for both solenoids and the other wires are the signal grounds coming from the PCM. I believe one is orange and yellow and the other is purple and yellow.

Years later, 3rd. Gen, purple/yellow IS the the solenoid ground-side (cold) connection from the PCM, for the TCC. So, proly same in '91. imp