Transmission Range (TR) Sensor

Overview - The TR sensor communicates the gear selector position that the driver selects to the PCM. The PCM determines a gear mode based on the TR input and the vehicle speed signal. The PCM then broadcasts a gear mode message over the communication link. The TCM uses the gear mode message to engage the transaxle in the gear that the driver selected. The other control modules use the gear mode message to control the rear lamps or a brake shift interlock solenoid. The TR sensor is mounted at the base of the gear selector assembly and the sensor shaft is moved by the selector.

Fig 1: Gear Selector Assembly

Courtesy of FORD MOTOR CO.

TR Sensor and PCM Interface - The TR sensor is a linear potentiometer device that provides the PCM with a percentage of input voltage proportional to the rotational angle of the sensor shaft. The TR sensor consists of:

3 independent (TR-A1, TR-A2 and TR-A3) signals.
2 5-volt reference (TR-VREF1 and TR-VREF2) lines.
2 signal return (TR-RTN1 and TR-RTN2) lines.

Fig 2: Transmission Range (TR) Sensor

Courtesy of FORD MOTOR CO.

The TR-A1 signal has a negative voltage slope, meaning the voltage decreases when the sensor angle increases. The typical TR voltage ranges from approximately 4.5 volts in the PARK position to approximately 1 volt in the LOW gear position. The TR-A2 and the TR-A3 signals both have a positive voltage slope. Voltages increase as the sensor angle increases. The typical voltage for the TR-A2 and the TR-A3 range from about 0.6 volts in the PARK position to about 3.5 volts in the LOW gear position.

The TR-VREF circuits are bussed together internal to the TR sensor, and both TR-RTN circuits are bussed together in the TR sensor. One of the TR-VREF and one of the TR-RTN circuits are dedicated signals from the PCM. This design of redundant signals protects against an open circuit condition.

Fig 3: Voltage Versus Angle and Gear Selected Chart

Courtesy of FORD MOTOR CO.

If the PCM detects a concern in one of TR signal inputs, it uses the other 2 TR signals to determine what gear the driver selects. If the PCM detects 2 or more TR signals that are invalid, the PCM:

allows the vehicle to travel in DRIVE position or LOW gear position if the vehicle was driving forward at a significant speed when the concern was detected.
allows the vehicle to travel in REVERSE gear if the vehicle was driving backwards at a significant speed when the concern was detected.
broadcasts gear mode - NEUTRAL over the communication link when vehicle speed decreases to 8 km/h (5 mph).
sets the DTC and illuminates the indicator light.