Myze

I have a 93 Dodge 2500 Cummins that's speedometer doesn't work, won't shift down when starting out from a stop, & will not shift into overdrive. If you manually shift it to low, & manually shift into second & drive it shifts fine. Once you get up to highway speed it won't shift into overdrive either. When I push the O.D. Off button off & on, it illuminates but nothing happens.

The prior owner I bought if from had driven it through some high water, & stalled it. It has had a complete transmission overhaul about 4 years ago, & only has about 20k miles on it. I just replaced the speedometer sensor that attaches to the side of of the transfer case which was missing, hoping that would solve the nonfunctioning speedometer & shifting issues. However, the speedometer still doesn't work, & the shifting problems haven't changed.

Since the wires coming out of the speedometer sensor didn't match the wires tied off, I took my best guess on the 50/50 chance of hooking them up backwards. Since I usually follow the 50/50/90 rule, I reversed them when the speedometer did not work & still nothing. I hope I did not fry the new sensor, as it was around $80. I also checked the fuses, & they are all good as well.

I was wondering if there are any other electrical devices that may have gotten wet & shorted out. Supposedly the water never made it up past the bottom of the dash....

Any suggestions??

wannadiesel

Does the VSS turn? Often the drive gets stripped.

Myze

I had to remove the drive to get the broken off square drive out of it from the previous VSS. I then screwed the VSS onto the drive while I had it out & turned the gear to make sure the VSS turned, which it did.

Later when I didn't get any speedometer activity, I removed the VSS from the drive, jacked the rear of the truck up & inserted a hex wrench into the drive. Started the truck & shifted into drive, & the hex wrench was spinning nicely.

Good thought though!

wannadiesel

Check to make sure you have continuity between the VSS plug and the PCM connector. White with an orange stripe at both ends for signal, black with light blue stripe for ground.

Myze

Dumb question I'm sure, but where is the PCM located??... I'm familiar with the acronymn ECM for Engine Control Module, but right now I'm having trouble with what the "P" stands for.

I did speak with the original owner this afternoon, & he said that the speedo & overdrive didn't work prior to the drowning. Said something about a cover near the top of the transfer case with some plastic gears that you can't get anymore driving the VSS drive which controls the overdrive? He wasn't very clear as he admits to not being mechanical, & was quoting a mechanic who worked on it for him years ago. As I mentioned earlier I did a crude check to make sure the drive was turning, but I was a one man operation & had no way to see what happened when the motor was rev'd up.

Anyway, appreciate the suggestions you have offered.

apwatson50

Since this engine doesn't have computer controls the "P" is Powertrain as its only function is to control the transmission, could also be considered a "body" control module as it controls A/C among other things.

There are 2 parts that go on the t-case, look in the sticky as I believe there are some good threads detailing the functions of them.

wannadiesel

The PCM is between the battery and the fender.

An ECM only controls the engine, a PCM controls the powertrain as a whole.

robjohn

Mine did that. Did some wire tracing, found a spot in the wiring harness where the two wires to the speed sensor were fused together. A couple days later the wires to the overdrive solenoid did the same thing. Not sure what caused it, maybe bad ground. Just to be safe I cleaned all the grounds and added a couple more. So far it is OK now.

raggmann

Is it an auto?
If so, I had the same issues on my old '92. I had the speedo drop off and it shift itself OUT of o.d. quite often.....odds are it's the TPS.