I’m asking this for a friend who maintains a fleet of Ram 3500 CTD chassis cabs for a seafood company. He has a ’98 that got a Jasper’s rebuilt tranny in the Spring. Since then, the "OD Off" and the "Trans Temp" lights have come on soon after startup. The tranny will not shift into OD (and the lights will not go out) until driving the truck for about 20 mins. Then, the truck will operate completely normally – no false light either. It all starts over the next morning, after the truck has cooled back down. My friend has used an infrared temp gun on the tranny pan when this happens – around 100 deg F (180 or so when fully hot), so the ATF is not actually hot. He has also tried snipping the wire that is supposed to send overheated ATF info from the sensor to the ECM or PCM. Nothing has helped change the way the truck first behaves.
Is there anything else that he should check? The tranny, solenoids, and wiring harness all check out OK according to him. Any help or suggestions will be greatly appreciated.

 

I wonder if the threw the 2000 and up temp sensor/pressure sensor into this truck? It would let the truck think that the tranny was never getting warm enough to go into OD, until you got to about 160-170 or so. The newer truck have a higher ohm sensor, so your truck would think it is "cold"

I'm not sure, just speculating--I put a new style sensor in an older truck and it freaked out, thought it was too hot.