Chrysler Repair: 1993 Dakota auotmatic transmission upshifts too soon, wont downshift, dodge dakota club, dakota club cab

Question
Hi Roland,

I have a 1993 Dodge Dakota Club Cab 2 wheel drive 3.9V6 4-speed automatic(A500) with 170,000 miles on it. I bought this truck new and have worked on it myself, except for warranty work.
The problem is when I'm starting out in DRIVE the transmission shifts all the way through 2nd, 3rd, and into 4th when I'm only going 15 or 20 mph, so I have to start out in 2nd and manually shift up to DRIVE when I get going fast enough. It won't downshift at all unless I manually shift it into 2nd when I slow down to about 25 or 30 moh. Then it will downshift into 1st. If I don't manually downshift it will shake the whole truck and stall the motor. I also don't have passing gear (kickdown). I have traced the 3 wires (dark blue, orange/light green, orange/dark blue or black) coming out of the Powertrain Control Module going to the 3-prong part throttle unlock/overdrive solenoid plug-in on the topside of the driver's side of the transmission. They are not shorted together or broken and I have checked the voltage on these wires and am reaading roughly 13 volts(ground to each of the other 2 orange wires) at idle. I have checked for error codes and they are 12(Memory standby power lost), 37(Part throttle unlock solenoid driver circuit), and 45(Governor pressure solenoid circuit).
  I tried unplugging the part throttle unlock/overdrive solenoid and now it upshifts and downshift fine except I don't have 4th gear, just 1st, 2nd, and 3rd and kickdown. If I plug it back in, my problem comes back. I changed the transmission fluid and filter aroud Christmas using Valvoline ATF+4 Full synthetic fluid instead of ATF+3 I had used in the past. Could this have made an existing problem worse because prior to this the transmisssion wouldn't always shift out of 3rd right away, but would eventually shift into 4th. This happened more when the engine was cold but it would also act up when it was at operating temperature, shut off, restarted and driven again. Also, for the past 2 or 3 years when I would be at highway speeds the transmission would shift back into 3rd on its own and the light on the O/D pushbutton would come on. I would have to press it several times to get it to turn off. Then it would upshift into 4th. At the present time though the button doesn't seem to be working.
  What do you think the problem could be? I know that whatever the problem is that error codes will have to be cleared once the problem is fixed. Will disconnecting the battery for a short time clear them or would I have to take I t to a transmission shop? HELP !!!!!!

Thanks for your time, Dennis

Answer
Hi Dennis,
Thank you for the detailed description. I am a bit limited in that all my manuals are for the car lines so the A500 is not a transmission for which I have the manual. But it appears to be similar for that time period to the A604 in being electronic and having similar, though not identical fault codes. My '92 manual for the 604 says for the code 37,
which is described as the solenoid switch valve being in the locked up position,seems consistent with what you are describing. As for remediation it suggests draining the fluid and examining for debris (which would prompt a rebuild) and if that is not present then to recondition the solenoid switch valve which is located, I believe, in the solenoid box. So you shouldn't have to rebuild the trans if you don't have a bunch of debris in the pans. I doubt the +3 or +4 makes a difference, just so long as it isn't dexron. Disconnecting the battery will erase the codes, and may temporarily correct the problem and then set fresh codes. So that is worth trying just to find out where you are at. The stalling out would indicate that the torque converter is indeed locked up when it shouldn't be. So if the solenoid switch valve were faulty that may be the cause of the inappropriate lock up. I doubt it is electrical, but rather hydraulic in nature.
I don't have a trans rebuild manual beyond that in the general services manual for that time period, so I can't give you specifics on the valve in question. But going through the solenoid box may be the most reasonable approach. I am very interested to learn what you find out.
Roland