I have a 93 Ram Diesel Automatic. I have posted in the EMERGENCY SECTION without getting this issue resolved. After having read some of the posts in here, I understand that if the blue wire to the tranny is cut, and a switch is inserted going to ground one can lock the overdrive on. Is my understanding correct? If so does the ground go to the tranny or to the module?
Here is my problem: I bought the truck used, the speedometer didn't work and the computer needed replacing. I initially tried a puter from a gas job and speedometer worked right away so ordered a new puter from the dealer. On installing it still no speedometer, hence no overdrive. Thinking puter was faulty got a replacement but to no avail. Speedometer did work when check engine light was on and also had overdrive. Took the truck to the dealer and 5 hours of diagnostics later, was told by mechanic he was certain puters were faulty and asked Chrysler to check their stock. Chrysler refused and said needed a new Crankshaft speed sensor. $200.00 later, with new sensor and no difference. Mechanic took truck dwon the road, shifted to nuetral shut truck off and turned key back on and speedometer works. With teh price of fuel today. would like the overdrive, can do without the speedometer although would be nice too, Speeding tickets are not cheap! Any ideas? Thanks
Paul

 

have you adjusted the tps ? check the sticky
check to see if the csp sencer is pluged in along with every wire that hooks to the tranny.

 

Before I bought the new PCM I put in a PCM from a gas job to check al wiring etc. Speedometer worked right away, mechanic at dealership also installed teh gas PCM module with same results, so all wiring must be good. His thoughts are the module, **** wish it was a standard!

 

If you switch the blue wire to ground you will fry a fusible link. The blue wire supplies current to the solenoid any time the key is on. You need to ground the wire that is NOT blue. That will ground the solenoid and complete the circuit. If the trans is in 3rd, it will shift into OD assuming the solenoid is OK and the OD clutch is not fried.

The PCM has nothing to do with the speedo, that is a VSS problem. Have you looked to see that the VSS is installed? They have a tenancy to work loose and fall off.

 

I have three wires going to what I beleive to be the VSS, Speedometer on this truck is electronic and definitely goes through PCM White with orange tracer has power when key is on, blue, no power and orange no power when key is on.
Thanks

 

The PCM and the speedo share the VSS. If the PCM fell off the truck, the speedo would still work, it is totally independent of the PCM. The PCM is not the problem here, your problem is the VSS or the VSS drive.

 

Okay, I had some time today and decided to try something here. I pulled the clip off of the VSS and also disconnected the PCM. Took a continuity check on all three wires. White with orange trace ended up on white with orange trace on the pcm, blue gave me one pin on the clip also.
When I checked the yellow, got these results:
Had continuity to red which is full power
got continuity to black with white trace,
got continuity to tan with yellow trace,
got continuity to orange with white trace,
got continuity to pink with red trace,
got continuity to black with pink trace,
got continuity to green with white trace,
and got continuity to green with red trace.
When I put the circuit tester on the blue wire and touched the positive terminal on the battery light came on, so blue is a ground.
The orange wire gave me nothing.
The yellow wire with the black tracer, which becomes orange at the connector appears to be a ground also.
Any ideas?

 

Yellow is the 8 volt supply to the VSS. Orange is signal, it splits and goes to the speedo as well as the PCM. Blue is ground. Check the VSS plug for 8 volts across yellow and blue with the key on.

 

Thanks for all your help. So I would assume since yellow is positive carrying current to the VSS when it is disconnected at the PCM and the module I should not get a reading when conneceted to a tester and the positive terminal of the battery, nor should I get a circuit if connected to teh negative terminal of the battery. Since when the yellow terminal is connected to one end of the test light and test light is touched to the battery, I get a complete circuit, my problem lies in the yellow wire and is going to ground somewhere? Is this a correct assumption?
thanks in advance

 

just check the two wire plug up by the shift linkage that is for overdrive one is a ground and one is 12v power. With a bad PCM you wont get power to overdrive selonoid. Run a switch to the wire that is not grounded when you get to the speed you want flip overdrive on then turn it of when you dont need it thats what i do on my truck works great.

 

That yellow wire supplies 8 volts to several sensors, you could be getting ground through any of them. It does not mean you have a problem with that circuit. What kind of test light are you using? Not a big 12v incandescent, right? Those things draw too much current for computer circuits.

The ignition switch supplies power to the OD solenoid, not the PCM. The PCM supplies ground.

 

The test light I was using is a proper probe test light for testing automotive circuits. With the PCM back on the harness I get 4.8 volts. When I install the module from the gas vehicle I get a reading of 7.9 volts. Any ideas?
Thanks

 

It sounds to me like the electrical stuff is working fine. Are you sure the VSS drive is turning the VSS? They get rounded off and stop working sometimes. If the VSS is not spinning, you get no speedo and no OD.

 

VSS is working fine, actually a new one was installed by trannie shop. Speedo and overdrive work fine when check engine light is on, and also works immediately with the PCM from the gas job with the exception that the speedo is very erratic with the gas PCM in there. Why would I only have 4 volts with right PCM and 8 volts with the one from the gas job? Thanks for all your efforts

 

Was wondering if there is any possibility that it could be the ignition switch, since if you are driving and throw truck in nuetral and shut switch off and then turn it back on without starting the truck, the speedo works. How hard is it to change the ignition switch? Thanks again.