no overdrive ? 1990 ram 350 van

3000 rpm @ 60 mph, overdrive light switches on and of but no shift, my low idle also seems higher, the van wants to strain while sitting at lights, and i lost my cruise control. I'm getting error message 37 - shift indicator light failure or part throttle lock/unlock solenoid driver circuit or solenoid coil circuit, and 41 - alternator field control circuit open or shorted. could any of these problems be connected? Could the shifting problem be with the lockup torque converter? I recently had an alarm w/remote start installed, took it back and they dont think it's related to what they did, ( they were pretty thorough but mostly look for wires that may have come loose. this is a 1990 Ram van 350 that had been converted into an ambulance, but i dont think that effects these problems, the 2 systems seem to be well isolated. Thanks to any and all replies.

Even with the OD switch off, you should have lockup in after it goes into 3rd gear. See if it does.


There is an overdrive solenoid inside the transmission that kicks the OD in an out with the switch. You could have a bad wire somewhere or solenoid is bad. Not sure of the test for this right off the top of my head.

With that 41 code check the voltage with a DVM at the battery with the engine running. You're probably going to find that your voltage is too low (probably right at 12 to 12.5 volts). A healthy charging system should be around 14 volts at the battery with the engine running.

If this is indeed the case, get your wallet ready, you'll be replacing the ECU as that is where the voltage regulator is located and it's not replaceable.

I have had the same (and more) problems. The fine people who use this forum have told me that proper voltage is critical. Without it the ECU may be picking up codes that are false because of bad voltage.

Good luck and let me know what happens.

A few random thoughts on your troubles that might help:

As regards what the fellow just said re the new ECU, also consider that just a weak / 'beginning to short out' battery might be the culprit.

I just had a low voltage problem - where I thought the alternator was faulty, turned out it was a battery less than a year old. This van has tons of built ins - its a conversion van - and only one battery - the starting battery -so it gets tons of use & abuse.

Made it fail in 10 months - Wal Mart gave me a new one for $ 0.

So, check that battery, if faulty it could mimic a bad regulator / ECU - PCM.

BTW, disconeecting your battery negative for a minute should reset your trouble codes, so at least you can see if that changes things, even if only temporarily.

Let us know how you fare,

David B.
RamVanMan

PS: when my '96 B-2500 runs hot (I think this is what causes it...), my OD won't kick in even if I press the dash switch, it still glows. If I stop and turn off the engine and disconnect my negative cable momentarily, it functions normally again. I have a 'quick disconnect' battery negative, so it's easy to do.