The transmission position sensor, also known as the transmission range sensor, is an electronic sensor that provides a position input to the Powertrain Control Module (PCM) so that the transmission can be properly controlled by the PCM according to the position commanded by the sensor.
1. Car does not start or cannot move
Without a proper Park/Neutral position input from the transmission range sensor, the PCM will not be able to crank the engine over for starting. This will leave your car in a situation where it cannot be started. In addition, if the transmission range sensor has completely failed, the PCM will not see any gear command input at all. This means that your vehicle will not be able to move at all.
2. Transmission goes into different gear than selected
There could potentially be a mismatch between the gear selector lever and the sensor input signal. This would cause the transmission to be in a different gear (controlled by the PCM) than the one selected by the driver using the shift lever. This could lead to unsafe operation of the vehicle and could likely become a traffic hazard.
3. Vehicle goes into limp mode
On some vehicles, if the transmission range sensor fails, the transmission can still be mechanically placed into gear, but the PCM will not know which gear that is. The transmission will be hydraulically and mechanically locked into one specific gear for safety, a situation known as limp mode. Depending on the manufacturer and the particular transmission, limp mode could be 3rd, 4th, or 5th gear, as well as Reverse.
Any of these symptoms necessitate a visit to the shop. However, instead of taking your vehicle to a mechanic, the technicians at YourMechanic come to you. They can diagnose whether your transmission range sensor is bad and replace it if necessary. If it turns out to be something else, they’ll let you know and diagnose the issue with your car so it can be repaired at your convenience.
This article originally appeared on YourMechanic.com as Symptoms of a Bad or Failing Transmission Position Sensor (Switch) and was authored by David Smith.