ASE G1 Auto Maintenance and Light RepairAutomatic Transmission/TransaxleMedium
A customer reports that their vehicle's automatic transmission occasionally fails to shift into overdrive (the highest gear), causing higher than normal engine RPM at highway speeds. All other shifts seem normal, and there are no dashboard warning lights. What is the most likely cause?
- AA faulty transmission range sensor (TRS).
- BA worn torque converter clutch (TCC).
- CAn open circuit in the overdrive shift solenoid.
- DA failing input speed sensor.
Show answer & explanationAnswer & explanation
Correct answer: C. An open circuit in the overdrive shift solenoid.
If only overdrive is affected, while other shifts are normal, it points to a specific issue with the component responsible for commanding or engaging that gear. An open circuit in the overdrive shift solenoid would prevent the hydraulic circuit for overdrive from being activated, thus preventing the transmission from shifting into that gear.
Why the other options are wrong
- A. A faulty TRS typically affects Park/Neutral safety switch function or incorrect gear display, not specific gear engagement like overdrive only.
- B. A worn TCC causes shudder during lock-up, not a failure to engage a specific gear like overdrive.
- D. A failing input speed sensor would likely affect multiple shift points or cause erratic shifting across the board, not just overdrive.
Shift Solenoid
Shift solenoids are electrically controlled valves within the transmission's valve body that direct hydraulic fluid to engage or disengage specific clutch packs or bands, thereby controlling gear changes.
- One or more solenoids control each shift.
- Controlled by the TCM.
- Failure can cause delayed, harsh, or missing shifts.
Memory trick: Solenoid, Sensor, or Valve Body, is the key to the specific gear mystery.