Need help, 94 12v Cummins no overdrive

[Doug senterfitt]

I already replaced the tps about 3weeks ago because it was going in\out of overdrive. Well it fixed it, it worked for 2weeks. Now I don't have overdrive at all, I've replaced the transmission temp sensor, the overdrive & tcc lock up solenoid. Fluid was good and clean. The overdrive off button light, lights up as soon as I turn the key on, the trans temp light doesn't come on with the overdrive off button. But the trans temp light does work, I see it turn on and go off as soon as I turn the truck on. I even changed the speed sensor in the side of the transmission, I've changed the gauge cluster and the ignition switch as well. I'm lost

 

[Timd32]

Have you rechecked the sweep of the TPS since it worked for a while after you messed with that. Maybe it's a bad harness or connector associated with that?

When you did the trans temp sensor did you ohm the new one, they make a 1k and a 2k sensor. Think you need the 1k.

Have you checked the 8pin connector on the trans? They have issues.

I'm actually at work today and won't be able to check my phone for many hours, we just stopped for a quick lunch... hope you can figure it out.

 

[Doug senterfitt]

Have you rechecked the sweep of the TPS since it worked for a while after you messed with that. Maybe it's a bad harness or connector associated with that?

When you did the trans temp sensor did you ohm the new one, they make a 1k and a 2k sensor. Think you need the 1k.

Have you checked the 8pin connector on the trans? They have issues.

I'm actually at work today and won't be able to check my phone for many hours, we just stopped for a quick lunch... hope you can figure it out.

I checked the tps it still shows its good, I replaced the temp sensor with a factory one from dodge, my transmission only has a 3pin connector. I'm not getting any codes either

 

[Timd32]

Ah. 47RH sorry about that was in a hurry at lunch, I'm usually the last to take lunch and the first to get up during these shutdowns...

Maybe someone else will jump in then with a quick fix.....

Yeah not too hip on those I cant seem to find a complete description of all those controls in the manual, found the 95 FSM focuses on a dash mounted switch, not sure how much a differs from a 94. Had to piece together a bunch of stuff for the below info..... as always disregard if way off base here...

Dug thru some wiring diagrams there are some circuits dealing with the OD.

Could it be an open circuit from the PCM 55 to the trans 3 pin plug, or that hot lt green/bk wire is not hot at the trans, or the switch signal is not changing state to pin 10 of the PCM?

PCM 10 OR/WT is the dash switch thing if you happen to have one.

On the trans Pin 2 LT Grn/bk should be hot, the other two are controlled from the PCM.

PCM 55 BRN is the Trans OD solenoid to pin 1 on the trans. It discussed in the Diesel section 14, it monitors engine rpm and vehicle speed verses TPS voltage, also needed are various inputs from the module timer.... but of course can't just list those inputs to save some time...

PCM 54 OR/BK is TCC Lock. Trans pin 3

TPS was at PCM Pin 22, maybe check it at the PCM? It says need DRB tool, but maybe you can see if there is an harness issue from TPS to PCM? Think Pin 6 was involved in that TPS deal. And the signal B- ref.

Does it have that switch and does the light work when you cycle it?

Could not really find the relationship in the wire diagrams and maybe it was TCC lock up related but the brake switch was brought up in a few very TDR old posts I dug thru.

Was way off on that temp sensor comment above it's like 11k-13k at 68F, 9k-10k at 77, less than 1340ohms with engine warm... learn something new, warmer is lower ohms, colder is higher (kohm)


This was the no 3-4 shift table in the 95 book...

 

[ANON KNOWLEDGE]

I have a 95 Dodge 3500 5.9L 12v Cummins w/47RH transmission. From approximately 2012 to 2/22/2020 I have had issues with no tachometer, no overdrive, cruise control, A/C. What is different about this situation is that the truck runs 100% in the summer time, but as soon as the cold temperature (around 45f and lower), the above stated components fail. This was a long process and is now solved.

Parts replaced,
1.) Engine Speed Sensor (ESS)
2.) Throttle Position Sensor (TPS)
3.) Powertrain Control Module (PCM), done by SIA Electronics.
4.) Vehicle Speed Sensor (VSS)
5.) Powertrain Control Module (PCM), done by Cardone through NAPA.

So, this was quite the headache... First, I do not have a lot of electrical experience. But this would be enough to really anger someone. So without further due, let this short story begin.
ESS and TPS did nothing. Came to the conclusion that it had to be the PCM. Sent the PCM to SIA Electronics, that was a mistake. I knew something was incorrect when I called them. I do not remember what it was for, but I asked them if they had sealed the circuit board with new silicone gel and they said yes, that was a lie. You could see the cut out areas where resoldering had taken place. For some reason I just left it at that and assumed the PCM was fixed. However, the failing components continued. I replaced the VSS because of its connection to the ESS, TPS and PCM. Still the problem persisted. From the beginning of this new year, I have had time to work on the wiring. After opening the wiring up in the engine compartment and checking the wiring running to the transmission, I finally came back to the PCM. I wiggled the wire harness up and down while the engine was running and sure enough there was tachometer movement. I had done this before and noticed it jump a little, but I shrugged my shoulders or something, because the PCM was just fixed. There were also times when moving the PCM/wire harness did not make any movement in the tachometer. After spending quite a while making sure that it was the PCM/wire harness connection, I spread the pins with a razor knife to check connection. Still no consistent tachometer. I then began researching where to bring the PCM for repair. I found that Cardone was the only company that stated that they re-gel or silicone the PCM circuit board. I also found through a lot of research that the OEM gel/silicone circuit board sealant tends to push the chips up on the board. After contacting Cardone, I was told that I had to bring it to an autoparts store to have it sent in. I first went to O'reilly's and was told it takes months. Cardone stated that NAPA among many others provide the required third-party mail in service. I decided to take it to NAPA. Another strange thing that happened is that both O'reilly and NAPA said they can't ship it at first and O'reilly's website said it had the PCM in stock?!?! I was also told it might not be repairable and that if there was a extra available to swap that I could opt-in. A couple weeks later and I walk into NAPA looking for my PCM. They had heard nothing. An hour later I get a call from NAPA saying the PCM came in this morning and is ready to go. That day, I installed it in the truck and EVERYTHING WORKS!!! Time for a test drive... I hit 55 MPH and the tachometer is headed for red-line. Sure enough, there is no overdrive. I ended up calling a mechanic who had worked on the transmission back in 2008. I brought the truck to his shop to run tests on the OBD1 system. His snap-on scanner read that the TPS was signaling wide open throttle or 5v, when it should be at .5v. For some reason I cleaned the stuck old TPS and kept it, most likely because I had purchased a cheap replacement. After the install of the old TPS, I took the truck down the road and there it is 4th gear, overdrive and everything is operational.

I did not put the technical electrical information in this post, I found a lot of it has already been addressed in other posts on the internet. I tried to write this as simple and straight forward as possible. I read through the manual and wrote down flash cards for the wiring colors, circuitry and voltage in my repair process. Before opening the wiring in the engine compartment, it would be a good starting point to check the PCM/wiring harness connection for tachometer movement. Of course this works easiest if the tachometer is completely dead. Checking all the following sensors and wiring near those sensors would be ideal for the next possible solution.

I can't even number the amount of threads, articles and posts I have read to solve this problem. It is not fun to go back to a part that was already replaced and/or repaired, it really disrupts the process of order and solution. Also, I searched for the overdrive circuit fuse and have yet to find where and what exactly that is. Hopefully I won't need to.

I hope this is helpful to someone in a similar situation. Go ahead and re-post this in an appropriate similar thread, as this does cover more than just overdrive.

-Anon Knowledge

 

[GAmes]

@ Anon Knowledge

Your frustration after the SIA "repair" is the exact reason why I have a couple of known good spares in my shop. I still have the original one as well that only needs an external voltage regulator to be used if I ever need it. These trucks are scrapped and parted out every day. One only needs to keep his/her ears open to find a spare PCM.

 

[ANON KNOWLEDGE]

Turns out my tachometer issue is not solved. The other day I started the truck in cold weather (~30 degrees) and the the tach bounced and went on and off before complete zero. I moved the wires connecting the harness to the PCM, this caused it to jump and even stay at ~750 RPM. I have done this before, but sometimes it will not effect anything. That is what originally caused me to send the PCM in for repair a second time.

I know the wires that are used for the tachometer, but has anyone else had this issue? I have searched the repair service manual and the internet and cannot find anything on how to repair the wire harness connector. The most likely solution will be extracting the wires from the connector, I just need to know what terminal pin extractor tool is required.

What would cause this to occur only in cold weather? The neighbor has an early 2000's Toyota Tundra and his lights turn on and off in cold weather when the vehicle is shut off.

For having hardly any electronics on this 95 dodge, this is very annoying.


95 Dodge 3500 5.9L 12v Cummins w/47RH transmission

 

[BigPapa]

You’re gap may be a bit to wide on the sensor.

Part of my 12-valve conversion was putting a tone wheel on the damper and mounting a 24-valve Crank Sensor. It worked flawlessly for over a year. I had to remove it to put a front seal in and that winter when it got cold, the tach wouldn’t work until I’d driven it about 10 miles and then it would start working. I adjusted the sensor as close as I could to the tone wheel and it’s worked perfect all year round.

 

[ANON KNOWLEDGE]

I re-adjusted the Engine Speed Sensor (ESS). The tachometer still had some bounce and even zero reading. I went back to the Powertrain Control Module (PCM). I extracted each of the wire harness connector pins (you only need a tiny flat screwdriver to extract) and checked for any signs of failure. Everything checked out good. I am thinking that there is something wrong with the male PCM pin(s) solder, because every time the tach drops out or bounces, if I wiggle the harness connector I can get the tach to hold steady or shutoff. What is strange though is sometimes it does not work. I have had it to where the the tach operates correctly no matter how I move the harness. Temperature is starting to warm up so this might take awhile. I may need to find someone with a 12V to test the PCM.

95 Dodge 3500 5.9L 12v Cummins w/47RH transmission