Problem: The vehicle will not shift and is stuck in second gear. The MIL is on.
Details: When the tech connected a scan tool, he found a DTC P0750 (LR Solenoid Circuit). The first step was to check the fluid level and condition. It was full and looked/smelled normal. Next, he tested the resistance of the solenoid pack. They were all in specifications so he tested for power and grounds to the solenoid pack. He found that the solenoid pack red wire was intermittently getting power. After looking at the wiring diagram, he tested the power and ground circuits for the transmission control relay. The circuits tested good so the relay was determined to be faulty.
Confirmed Repair: He replaced the transmission control relay, cleared the code and test drove the vehicle. The transmission shifted correctly again and the MIL remained off.