ASE G1 Auto Maintenance and Light RepairAutomatic Transmission/TransaxleEasy
Which of the following is the primary purpose of the transmission range sensor (TRS), also known as the neutral safety switch, in an automatic transmission system?
- ATo measure the speed of the output shaft for shift timing.
- BTo prevent the engine from starting unless the transmission is in Park or Neutral.
- CTo regulate the hydraulic line pressure for smooth shifts.
- DTo detect excessive fluid temperature and alert the driver.
Show answer & explanationAnswer & explanation
Correct answer: B. To prevent the engine from starting unless the transmission is in Park or Neutral.
The primary purpose of the transmission range sensor (TRS), or neutral safety switch, is a safety feature that prevents the engine from starting unless the transmission is in Park or Neutral, thereby preventing accidental vehicle movement upon starting.
Why the other options are wrong
- A. This is the function of the output speed sensor.
- C. This is the function of the pressure regulator valve and pressure control solenoids.
- D. This is the function of the transmission fluid temperature sensor.
Transmission Range Sensor (TRS)
The Transmission Range Sensor (TRS), or neutral safety switch, identifies the selected gear position (P, R, N, D, L) and sends this information to the PCM/TCM, also serving as a safety interlock.
- Located on the outside of the transmission.
- Prevents engine start in any gear other than Park or Neutral.
- Also used for gear display on the dashboard.
Memory trick: Park, Neutral, Start, no other gear will impart.