MEL79000

Howdy All, I am dealing with a blinking AT Oil Temp light and am interested to hear if anyone has any thoughts as to what may be wrong. Below is all of the background information to date. 1. The light first came on after driving 100+ miles on a rough (washboard) dirt road. 2. There is absolutely no difference in how the car drives. 3. The diagnostic trouble code is 77, which is for the lock-up duty solenoid. 4. My mechanic recently dropped the pan and said all the solenoids look fine. He replaced the fluid and filter and buttoned her back up. 5. I took a drive to the mountains the other day approx. 1.5 hours of mixed highway and backroad driving. On the drive to the trailhead there was no light. Hiked for around 5 hours and drove home. After around an hour the light came on, while on the highway. Again, there is still no change in how the car drives. 6. I spoke with my mechanic today and he thinks there may be some temperature sensor that is damaged. He is confident that if the lock-up duty solenoid was busted I would definitely be missing my overdrive and would notice the difference. It is a big mystery at this point, so any thoughts would be helpful. Thanks for your help!