Engine/Transmission (1994 - 1998) Lost Overdrive

[SFPADGETT]

1995 CTD, 2500 4x4 ext cab, auto, 415,000 miles



Stopped for 15 minutes after a 1-1/2 hour drive on interstate at (65-70 mph) with transmission working fine (running empty). Started trip again and no overdrive--checked fluid-- still in hash area, still bright red, didn't smell bad/burnt. Took back roads home keeping under 55mph for 2 hours! Next morning on the way to our shop (after having stopped overnight) it shifted one time into OD, but came back out right away. Having a fresh rebuilt trans at shop we installed with new valve body and overdrive solenoids--but no joy.

Since then we have tested and swapped out known good parts:

tps

brake light switch

head light switch

overdrive on/off switch

over drive solenoids (again)

valve body (again)

powertrain control module

speed sensor in transmisstion

speed sensor in rearend

transmission temp sensor

checked and rechecked all fuses



It does have 12volts in center pin of 3 pin connector that plugs into OD switch on transmission.

Truck drives good, shifts good (well at least 1,2,3) no other problems, all electrical things work in truck. Only "extra" electrical are Hella fog lights, and louder horns (both have been on truck over 10 years). Transmission temp (sending unit in pan) never goes over 190 when pulling trailers (usually in the 140-150 range in summer, stop-n-go city driving without trailer)



Any Ideas? Suggestions?

 

[budnate]

sounds like maybe your computore took a dump, you have checked everything else, if I was at your point I would unhook the batteries and leave them unhooked for a hour or so and rehook and see if it comes back... do 95's have to be up at least 45mph before they lock up like the 98's??? maybe you lost speedo feedback to the pc??

 

[SFPADGETT]

We swaped the PCM (Powertrain Control Module) with another 95 truck that we have (it works fine in the other truck) and had the battery loose for about 3 hours while we were checking wires / switches, etc. (but no change)

The convertor locks up depending on pedal pressure, but it is locking up currently in 3rd gear around 45

Cruise works fine from about 40 to 55 (I have not tried it at other speed ranges)

 

[budnate]

you got me. . looks like you have covered it all... . silly question your not running the same converter right??

 

[SFPADGETT]

Nope, new converter. At this point there are "no silly questions", just questions

 

[JLandry]

SFPADGETT,



Have you checked for continuity (a complete continuous connection) of each wire in the wiring harness between the PCM and the transmission?



If not, do you need to know which wires to check, or do have a copy the factory service manual already?



Regards,



John L.

 

[SFPADGETT]

yes, we rechecked the wires from the: TPS; trans temp sensor; and od sensor to the PCM this morning.

We are checking ALL of the other wires from the PCM to the various locations at this time (using the factory manual)

 

[JLandry]

A Chrysler DRBIII scan tool (or the equivalent from Snap-On, etc. ) could be very helpful in diagnosing where the problem is because it can show you all of the switch states, sensor outputs / inputs, transmission gear positions, temps, pressures, etc. in real-time. For example, if you could see that the PCM thinks the OD switch state is OFF, then you'd immediately know that's the problem and could go after it. Or maybe the PCM isn't seeing the correct input from the TPS? Or the correct transmission temp, etc.



Any Chrysler dealer will have a DRBIII or one can be rented from Miller SPX. They can also be purchased used on eBay (not cheap).



John L.

 

[SFPADGETT]

Sorry for being away from the post--had Strep Throat and didnt feel like working on the truck.



We have a SCAN tool for our fleet, it shows the TPS with . 81 volts at idle and 2. 97 at WOT (not quite the 2. 2 volt rise as the manual says, but has worked like this for years) New TPS installed and ranges are similar. Linkage is at 5" (dead on). We have installed a new circuit--taped into the trans and installed a switch to act as a ground for the overload solenoid so I can now force the transmission to recieve the ground signal to force the shift into overdrive. Still dont have a real solution and now considering a dial Pot to install in dash, but would rather have the truck work like it should

 

[SFPADGETT]

I was wondering, does the shaft that turns the TPS wear out? Maybe it needs to be replaced or the bushing that it inside the spring return on the mount for the TPS

 

[WilsonF]

If you decide that it might be the TPS contact this guy.
-- Specializing In Diesel Performance and Custom Fabrication --
He has a wired kit to install the pot type TPS for $30. Its for the 1 genners but he has been testing it on some 2 gen to see if it works.

Floyd

 

[SFPADGETT]

Thank you, I contacted him yesterday and he will let me know by the end of the week if the 2nd gen kits are ready

 

[SFPADGETT]

Wired around the TPS with a POT, but still know overdrive. Tried settings of 1. 0, 1. 5,2. 0,2. 5,3. 0 , 3. 5 and 4. 0 volts with the 5K pot.



HELP please , this thing is driving me nuts!

 

[SFPADGETT]

"know" should be "No", sorry, for the typo

 

[BSMcCauley]

Long shot: a long time ago my transmission refused to go into overdrive and the cause was the pin inside the trans temp sensor socket was bent and didn't match right with the plug on the wiring harness. Resulted in bad trans temp reading to PCM and setting some kind of "limp mode". Straightened the pin and got the plug & socket together correctly and haven't had that problem again since.

 

[SFPADGETT]

Thank you for the idea, I will check that plug and the others going to the trans and sensors to see if any of them are "bent". So far the PCM is not showing any codes.

 

[fest3er]

Fix the only thing left that might affect transmission operation: the charge air temp sensor (back of engine near fuel filter; perhaps it's unplugged). Maybe the PCM thinks it's -80F and won't allow overdrive until it warms up.

 

[JJanetka]

have you tried grounding the od leg with a switch to see if it will shift manually?

 

[SFPADGETT]

fest3r--I will check it shortly, but I didnt think it would be a problem as the grid heaters cycle on/off normally and the "wait to start" light works--but I will check it.



JJanetka--yes, I have installed a jumper wire with a switch so I can shift into OD as needed



Thank everyone for the suggestions--any more?

 

[SFPADGETT]

Problem found and solved!



Since the OD works with the extra switch and ground wire. I went back and ran a new wire from the OD plug in harness (on the trans) to the PCM (pin # 55)--and it works!



It seems that although the factory wire checked for continuity and was "good", it was not allowing the voltage (amp draw) to be strong enough to pull the solenoid in and function. With the orginal wire out of the harness and disconnected is still checks for continuty, but when we try and light a 9004 headlight bulb (our test load) it doesnt even glow. We tried it with a spare OD solenoid pack and it will not pull it in either.



So the moral of the story, even though a wire checks "good" with the ohm meter, if it will not carry the current, then it still could be bad.



Thank everyone for the help and suggestions.