Transmission range sensor explained
Transmission range sensor (TRS) or neutral safety switch is a protection device used to prevent a vehicle’s starter operation in all other gears except “Park” or “Neutral.” The TRS relays information about current gear selection to the Transmission Control Module (TCM).
Cars manufactured with automatic transmissions are intended to start only in park or natural. The vehicle and driver’s safety may rely on this feature. If the car starts in the wrong gear, it may accidentally move in the wrong direction unintended. For this reason, automotive companies began installing range sensors that prevent the starter controls in any gear besides park or neutral.
After a while, the transmission range sensor may start to fail or wear out. There are a few symptoms that are noticeable when this happens.
Car does not start or go into gear
Without the transmission range sensor relaying the proper “Park” or “Neutral” setting, the Powertrain Control Module (PCM) will not know how to start the engine. If the transmission range sensor has gone out, the PCM will not receive any gear command at all, rendering the vehicle immobile.
Transmission does not go into selected gear
If the TRS becomes worn out, it could send the wrong gear information to the PCM. This could cause the PCM to send a command to a different gear than selected by the driver. If the TRS sends incorrect information, causing the wrong gear selection, an accident can happen.
Some vehicles can still be manually placed into gear when the range sensor fails. Doing so will bypass the PCM, and the TRS will mechanically lock into a specific gear. The bypass is what is known as “limp mode.” Depending on the manufacturer and the transmission design, the limp mode may be locked into 3rd through 5th gear or Reverse.
Additional warning signs of a faulty TRS
If the vehicle has a defective transmission range sensor it will
- Not start
- Start in the wrong gear
- Cause the “Check Engine Soon” light will come on and stay on
The transmission range sensor was designed to keep vehicles and their owners safe by preventing the car from starting in the wrong gear. However, even things that are designed to keep us safe can wear out and cause protentional harm. If you suspect that a faulty transmission range sensor is causing your transmission problems, ask an Expert to help find a solution.