2001 Hyundai Elantra transmission temperature sensor problem

my 2001 Hyundai elantra has had some shift flares and twice gone into "safe mode" in about a years time. I recently had the car in for inspection and the check engine light was on. The mechanic put his scan tool on the car and it was showing codes for emissions issues. the mechanic repaired the emissions trouble but when I picked up the car he said it also said the transmission temperature sensor was saying it reads -40. I changed the sensor and drove the car a couple weeks. I took it back to him to see if the sensor would read anything different. He put his scan tool back on it and it still say -40. He tried to clear the reading but says it would not go away. Since then I tested the old sensor. It reads 8.36 ohms. The new sensor reads 10.23 ohms. the harness tests out at less than 1 ohm. The gray wire on the control module seems to be putting out 3.92 volts. does anyone have a idea of what I should check from here. The transmission has not gone into safe mode for 4 months and the engine light has not been on for the same length of time.
Thanks,
Mike.