Strange issue

93 929 stuck in overdrive mode. Vehicle starts in overdrive won't downshift or upshift. Slow take off. Hold button doesn't light up on dash. It only will downshift if placed into 1 on shifter and then move it to "s" for next gear and move into "d" for same gear as "s"

When the problem goes away it shifts without issue and the hold light becomes available.

I can tell when the issue will be present before driving the car. If I turn the key to the on position and press the hold button and if it doesn't light up on the dash the issue is there.
If the hold mode lights up on the other hand then the problem isn't there and it's ok to proceed to cranking up driving without issue.

Interesting! :ohmy: I checked out the transmission wiring diagram for direction:



Because the Hold indicator isn't lighting up, AND the transmission doesn't shift correctly, I'm guessing that the transmission module is actually dead when the problem occurs. Looking at the diagram, I see the module gets key on power on two pins from the 'Meter' 10A fuse. This same fuse also powers the park/neutral switch, which is where the Hold button resides (according to the diagram, anyway).

The next time you get this thing to act up, use a test light/multimeter to check for power at the Meter fuse. It's not gonna be blown, we just want to know if it's getting power or not. If it isn't, then the ignition switch is suspect. If it is, then we'll want to do some further checks at the park/neutral switch or the transmission module itself.

I checked meter fuse and when the problem is there I'm getting voltage on both ends of the fuse 14.26v while running.

Thanks for that! It's a swing and a miss, but still a test worth doing.

I think the next move is to go directly to the transmission module and recheck for powers and grounds there. Three power feeds, two are key on sources from that Meter fuse, pins 1P and 1N, both black/yellow wires. Then there's a constant feed, pin 1A, blue/red. Lastly one ground, pin 1J, blue/light green.

If we have all those when the symptom happens, then I'd tend to think that the module itself is suspect.

You might find this video helpful.



Sent from my Moto E (4) Plus using Tapatalk

I pulled the tcm out and checked the wires they are correct . Ground wire stays at 0 volts . Two power feeds with key on shows 12v.
I also checked the hold wire and with key on it shows 12v I pressed switch stays at 12v key on.

I got some more helpful info. When the hold light is available at key on and it lights up the voltage at the tcm hold wire shows 0.6 voltages. And if it kicks off on its own the voltage at the hold wire tcm shows 12v. It seems to be shorted and getting consistent voltage somewhere causing it to stay on overdrive mode.

If the hold light is not available<hold light not lit> at key on the tcm hold wire is would show12v engine off. But when it's working it shows at 0.6volts with hold light on.

I have also disconnect the tps sensor to force the hold light to flash continously at key on. This only works when the hold light is available and working correctly. Now if the hold light isn't available and I redo the same test I never could get the hold light to flash.

It's not even reacting to the sensor being disconnected when it's acting up.