The possibilities are as follows:
- Speed sensor
- Electrical Wiring
- PWM Solenoid / pressure sensor (typically replaced together)
- Internally broken parts
The Dodge 4xRE RWD transmissions are descendents of an earlier design. Before computer controls they used a centrifugal governor and throttle cable to control shifts. When GM and Ford went to computer controls they used a PWM (pulse width modulation) solenoid for mainline pressure and solenoids for shifting, eliminating the throttle and governor systems. Dodge left the throttle cable, and replaced the mechanical governor with a PWM solenoid and a pressure sensor controlled by the computer. With the exception of 4th, as it is independently controlled by the computer via it's own solenoid, the 4xRE's all depend on the governor pressure to know which gear to be in.
We were fortunate to have a 44RE core to steal parts from.
First was getting it here, it would be a long drive in 2nd, so I had him pull the electrical connector off, hoping for third. I didn't know if this would work or not, depending what was wrong, but fail-safe is third so it was worth a try. It worked, so the actual transmission was OK, just something in the controls. (Note: even with the electric off, if it was still stuck in 2nd, it could still have been the governor solenoid stuck)
- The speed sensor is a 1 minute swap, we had one, so that was the place to start. But it made no difference.
- A visual inspection of the wiring showed no problems, and we didn't have a spare computer to try (that would be #4 anyway).
- The Governor solenoid / pressure sensor combo is a very common problem with these transmissions, what happens is over time they get fine metal shavings in them until the solenoid sticks (it is a magnet). This was my guess from the start, but you have to drop the pan to get too them, so don't overlook something obvious. We dropped the pan, swapped them with the ones off my junk tranny (Note: these are such a common problem it is recommended to replace with new every time. He didn't have the money for new, so used it was) That solved it, had 4 forward gears and he was happy.
- While you have to drop the pan to get to the sensors, they are east to access, being bolted to the bottom of the valve body, on their own little block of aluminum.
- KEEP IT CLEAN! Any dirt is very bad inside a valve body.
- USE A TORQUE WRENCH ON THE VALVE BODY! They are particularly sensitive to that sort of thing. (35in lbs. I think)
- There is an alternative setup for this using a GM PWM solenoid. They claim it stops this sort of thing from ever happening again. I haven't tried one yet, but definitely would, especially on a tranny that has given me problems.
- Don't overlook the obvious, Yes, I was right this time, but it could have been something else. Like the speed sensor, and if I'd gone with my gut and been wrong, I'd have spent an hour fixing something that would have taken a minute.
- Most vehicles fail-safe to third (actually direct drive, could be 4th in a 5 or 6 speed auto tranny) in drive, and the manual 1st, 2nd, etc. still work. You can manually shift these to prevent damage - Fail-safe third is third all the time, you will eventually damage something if you don't.
- The background may be over-simplified, but contains enough information for my purposes.