Transmission Position Sensor/Switch: Description and Operation

ENGINE CONTROL COMPONENTS

Transmission Range (TR) Sensor

Overview
The TR sensor communicates the gear selector position 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 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 on the transmission assembly and the sensor shaft is moved by the selector shaft.







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:
- two independent signals (TR-A1 and TR-A2)
- two 5 volt reference lines (TR-VREF1 and TR-VREF2)
- two signal return lines (TR-RTN1 and TR-RTN2)

The TR-A1 signal has a positive voltage slope, meaning the voltage increases when the sensor angle increases. The typical TR voltage ranges from approximately 0.7 volt in the PARK position to approximately 3.8 volts in the LOW gear position. The TR-A2 signal has a negative voltage slope. Voltage decreases as the sensor angle increases. The typical voltage for the TR-A2 is approximately 4.3 volts in the PARK position to approximately 1.2 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 internal to 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.







If the PCM detects a concern in one of TR signal inputs, it uses the other TR signal to determine what gear the driver selects. If the PCM detects one or more TR signals that are invalid, the PCM:
- allows the vehicle to travel in the DRIVE 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 malfunction indicator lamp (MIL).