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 1: Identifying Transmission Range (TR) Sensor Connector Terminals

  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 2: Voltage Versus Gear Selected Chart

Courtesy of FORD MOTOR CO.

If the PCM detects a fault condition 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 fault was detected.
• allows the vehicle to travel in REVERSE gear if the vehicle was driving backwards at a significant speed when the fault was detected.
• broadcasts gear mode - NEUTRAL over the communication link when vehicle speed decreases to 8 km/h (5 mph).
• sets the diagnostic trouble code (DTC) and illuminates the indicator light.