I would really appreciate if anyone could give me advice about this. This past Friday, we drove our 1998 Dodge Grand Caravan (3.3L) about 3.5 hours to Jackson, MS (half-way point on a trip). When I was still on the interstate getting ready to exit, it suddenly felt and sounded like we ran over a washboard. After a few seconds the same thing happened, and then the transmission was no longer in gear (I assume...I do not know much about cars). Basically, the rpms went way up. I let off the gas and when I pressed it, the rpms went up again but the van would not accelerate. I coasted off the interstate and stopped on the side of the road. To make a long story short, after trying to drive the van and see what would happen, this was the situation:
When first driving the van, it would accelerate into first and then I think second gear. Then, when I got up to 20 - 30 mph, it felt like it slipped out of gear, the rpms sent up, and it would not accelerate. If I let the speed drop back down, it would then accelerate again but then do the same thing once I got up to 20 - 30 mph. Then, after I let the speed drop a second time and accelerate, it would then stay in second gear. I could then drive the van. To get home, we had to drive it this way. We did not let the rpms get over about 4000 (speed was about 45 - 50 mph).
I took the van to an Autozone and they did a computer scan. The results were:
Definition: P0731 - Gear ratio error in first gear
Explanation: The ECM has detected that the transmission input rpm does not match the transmission output RPM under known conditions.
Probable Cause: Check other service codes first; TSS error; Poor electrical connection; Internal transmission fault
Definition: P0720 - Low output speed sensor above 15 mph
Explanation: Vehicle speed above 15 mph while transmission output shaft speed below 60 rpm.
Probable Cause: Failed output shaft speed sensor; Electrical problem.
Definition: P0733 - Gear ratio in third gear
Explanation: The ECM has detected that the transmission input rpm does not match the transmission output rpm under known conditions
Probable cause: Check other service codes first; TSS error; Poor electrical connection; Internal transmission fault
Definition: P0732 - Gear ratio error in second gear
Explanation: The ECM has detected that the transmission input rpm does not match the transmission output rpm under known conditions.
Probable cause: Check other service codes first; TSS error; Poor electrical connection; Internal transmission fault.
Definition: P0700 - Transaxle control system fault
Explanation: ECM received a signal that the transaxle control module has a fault.
Probable Cause: Shorted or open circuit within transaxle; Failure of transaxle control module.
Definition: P0403 - EGR system fault (exhaust gas recirculation)
Explanation: The ECM has detected a fault in the EGR solenoid circuit.
Probable Cause: Failed EGR vacuum solenoid; Open or short circuit condition on the EGR solenoid circuit; EGR solenoid faulty; Failed EGR pressure sensor where applicable; Failed EGR position sensor where applicable
(Sorry for all of this information but I wanted to make sure to include everything in case I left out something important)

Could this be an electrical and/or sensor problem where this will not require a transmission rebuild / replacement?
We bought this van used, did not pay much, and have been told it probably is not worth paying for a transmission rebuild ($2000+ ?) if that is what it needs.

Also, in case this helps, if I drive it slow, right as it slips out of gear (after getting up to 20 - 30 mph), I can feel a slight rumble similar to what happened when this problem initially occurred.

Thanks for any help!

 

Not a transmission guru by any means but based on cost I would drop the transmission fluid pan and inspect for metal debris. If you see much more than the typical tiny fuzz on the magnets it's time for a rebuild. Change the fluid (ATF+4 only) and filter while you're at it. If all looks good change both the input and output speed sensors. Posting the codes would have helped.

 

Thanks for the advice. I edited my original post and put in the codes.

 

Could try changing the input speed sensor since you have a code for it (P0720) but with that many gear ratio codes I would say (not a guru) you have a rebuild in your future. They usually indicate slipping and worn clutch plates. A shop can read clutch volume index (CVI) numbers and confirm that.

To my eyes their explanation for a P0700 code is out to lunch. It hardly means the TCM has a fault. It does mean the TCM has recorded a fault. That fault could be the TCM or a couple dozen other causes.

If Master Tech doesn't chime in here send him a private message. He is the guru.