Engine/Transmission (1994 - 1998) Overdrive Not Working

[Black Bear]

OK I've got a 1998 2500 with the auto transmission, and just yesterday morning the overdrive quit working. We ran it the evening before and it worked like a charm, start it up in the morning and head to work and it will not shift into overdrive. I unplugged the wires going to the overdrive off switch thinking that maybe the switch was bad but that didn't help. So has anyone had this problem? What should I be looking for?



Merle

 

[Black Bear]

Update: the overdrive off switch seems to work fine. I just changed the bulb in the dash for it and it cycles like it is supposed to with the switch.

Merle

 

[cerberusiam]

Does that mean the OD still does not engage?

Add another mystery switch to ground the OD circuit and see if it still engages. That will tell you where to start looking, mechanical or electrical.

 

[Black Bear]

No the OD still does not engage, however the light on the dash works like normal.

How would I go about grounding the OD circuit?

I have hooked a scanner to it and have four DTC codes,
P0743-Powertrain
Torque Convertor Clutch Circuit Electrical (I think this may be caused by the Mystery Switch)
P0753-Powertrain
Shift Solenoid "A" Electrical
P01399-Powertrain
Wheel Speed Sensor 2-G- sensor curcuit intermittent
P1765-Powertrain

I just got these codes and have not done any searching as to what they mean yet.

[edit: I forgot to mention, I had previously relocated the OD lockout switch to the dash, so the wires no longer go thru' the shifter or the steering column]

Merle

 

[cerberusiam]

P0753 (M) Trans 3-4 Shift Sol/Trans Relay

Circuits

An open or shorted condition detected in the overdrive

solenoid control circuit or Trans Relay Circuit in JTEC RE

transmissions.





Likely that is the source of the lack of OD. Should be pin #6 on the trans control harness next to where you tapped the TC lockup switch. You can do the same thing and validate the solenoid is working. I *think* the codes are correct but a 98 12V is a big munge of things.



The wheel speed snesor code will also cause OD to not work or drop intermittently. Might be worth replacing the sensor on the diff and see if that helps. You can laways wire up the switch afterwards to validate the solenoid is not the issue.

 

[Black Bear]

OK I got the speed sensor on the way from my local O'rielly Store. I will post back when I get that installed.

In the meantime, to install the mystery switch the orange (w/black stripe) wire was tapped. that is on pin 11 at the pcm.

There is no wire attached to pin #6 at the pcm.

Merle

 

[cerberusiam]

Just unplug the harness. The pins should be marked on the plug.

 

[Black Bear]

I replaced the speed sensor, (after the kid at the O'rielly sent me a set of points instead of my speed sensor) that did not cure the problem.

So I tapped the wire coming from pin 6 on the round 8 pin plug and hooked it to a switch that would ground it, that has not cured it. So I guess that points to a faulty solenoid.

Merle

 

[cerberusiam]

The only other thing to check is the relay to make sure you have power on the harness connector. If your TC lockup switch works and the trans is still shifting OK then it likely has power and the solenoid is Tango Uniform.

I don't have a schematic to make sure #6 is the OD like the later trucks so that may be worth checking into.

 

[Black Bear]

Got the solenoid Changed! It works perfectly!!!!!!!!

Thanks alot "cerberusiam" you've been a great help!