Fluid Temperature Sensor

The fluid temperature sensor is located within the gearbox on the valve block. See Fig 1 . The EAT ECU uses this sensor to monitor the gearbox fluid temperature.

When the fluid is cold, the EAT ECU changes gear at higher engine speeds to promote faster fluid warm-up. If the fluid temperature becomes too high, the EAT ECU transmits a cooling request on the CAN link to the ECM to operate the cooling fans.

The fluid temperature sensor has an electrical output to pin 39 of the EAT ECU which also provides an earth path for the sensor.

The fluid temperature sensor is a negative temperature coefficient sensor. As the temperature rises, the resistance in the sensor decreases. As temperature decreases, the resistance in the sensor increases and the output voltage to the EAT ECU changes in proportion.

The output voltage from the sensor is in the range of 0-2.5 Volts with the lower voltage representing the highest temperature.

The change in resistance is proportional to the temperature of the gearbox fluid. See FLUID TEMPERATURE SENSOR RESISTANCE VALUES  table. From the resistance of the sensor, the EAT ECU calculates the temperature of the gearbox fluid. Should the fluid temperature sensor fail the EAT ECU uses the last recorded EAT ECU value as a default value.

The fluid temperature sensor can fail in the following ways:

• Sensor open circuit.
• Short circuit to 12 or 5 volts.
• Short circuit to earth.

The EAT ECU will detect temperature sensor failure when the vehicle speed exceeds 12.5 mph (20 km/h) and the temperature sensor provides a reading of less than -30°C (-22°F). In the event of a fluid temperature sensor signal failure any of the following symptoms may be observed:

• Upshift to 5th gear inoperative.
• Torque reduction request from the EAT ECU to the ECM inoperative.

Fig 1: Fluid Temperature Sensor

Courtesy of LAND ROVER NORTH AMERICA, INC.