I have a AT 2004 mazda 6i, and when driving for a while on the freeway, it will not stay in fourth gear. The car will jerk then just drop into 3rd gear, and the AT light and check engine light will both come on. If i pull over, the AT light will turn off but the check engine light will stay on. Then i have to drive no more than 60 MPH if i want the car to stay in 4th long enough to get me where i want to go. After my engine is off and has time to rest, the car will easily stay in fourth gear but the check engine light will stay on for a couple of days. Any ideas on what is wrong? Im thinking transmission sensor.

 

try reseting your ecu, if it doesnt work or the problem continues, you may need a new TCM