Hyundai Repair: 2001 Santa Fe transmission stops shifting, santa fe 2, transmission harness

Question
My 2001 Santa Fe 2.7l suddenly downshifts to 3rd speed while in drive and wont shift lower than 2nd in manual mode unless I turn off the ignition and restart, which will resolve the problem for a while. My mechanic reset the computer a couple of times but it reoccurs. The engine light has been on a few months now, my mechanic says it's a transmission fluid temp. sensor code. This vehicle has 175,000kms, should I have the tranny flushed or just get the sensor changed at the same time?

Answer
Flushing the transmission will be of little use toward resloving this issue.  Usually, when a fluid temperature sensor code sets, the problem is with the sensor itself, but is sometimes in the vehicle or transmission harness.  Since we know the problem goes away upon restarting the vehicle, it's likely that it's intermittent enough that testing will not conclusively identify the problem.

I'd recommend replacing the sensor.  This will require draining and filling the transmission fluid.  While this isn't a full flush, it does satisfy the recommended maintenance on this vehicle.