What is the Transmission Position Sensor (Switch) all about?
Vehicles equipped with an automatic transmission are designed to start only in park or neutral gears. If a vehicle is able to start in reverse or drive gears, it can unintentionally move, causing damage to property or injuries to occupants or bystanders. For this reason, automakers have developed a safety shutdown called a transmission position sensor or range sensor that cuts the power to the starter control circuit if the vehicle is not in park or neutral. This sensor or switch is typically mounted on the side of the transmission and screws into the body of the transmission to detect in which gear the transmission is engaged. If the driver attempts to start the vehicle when the transmission is engaged in a gear other than park or neutral, power is not distributed to the starter circuit. The vehicle will not crank, preventing unintentional vehicle movement. If the transmission position sensor, or range sensor fails, the vehicle may be able to start while engaged in a drive gear.
Keep in mind:
- Symptoms related to the transmission position sensor mimic those of other common problems.
- Professional mechanics need to diagnose the symptoms for accurate repair.
- The transmission position sensor is also commonly referred to as a transmission range sensor.
How it's done:
- The faulty transmission position sensor switch is identified
- The vehicle is lifted and supported on jack stands
- The defective transmission position sensor switch is then removed
- The new transmission position sensor switch is installed and the vehicle taken off the jack stands
- The repair is verified and the vehicle is road tested for proper operation
While the transmission position sensor is does not require any routine service, as an electronic part, it can fail. If your automatic transmission-equipped vehicle is able to start in a gear other than park or neutral, or if your vehicle will not start when in park or neutral, you may need to replace the transmission position sensor.
What common symptoms indicate you may need to replace the Transmission Position Sensor (Switch)?
- Engine will not start at all
- Engine will only start in neutral gear, not in park
- Engine will start in engaged in drive or reverse gear
How important is this service?
If your vehicle is able to start in gear, there is potential to cause injury to people or damage to property. If the range sensor fails, have it replaced immediately.