L322 Range Rover System Description and Operation
AUTOMATIC TRANSMISSION – ZF 5HP24
44-2-34 DESCRIPTION AND OPERATION
Transmission Temperature Sensor
The temperature sensor is located inside the wiring harness in the fluid pan and is connected to the EAT ECU with
two wires. The sensor is a Positive Temperature Co-efficient (PTC) sensor which has a semi-conductor material which
increases its resistance as the temperature increases.
The sensor receives a predetermined current from the EAT ECU on one of the wires and is connected to earth via the
ECU on the second wire. The EAT ECU measures the returned voltage and using this information calculates the fluid
temperature.
In the case of low fluid temperatures, the EAT ECU prohibits torque converter lock-up to promote faster fluid warm
up. In the case of high fluid temperatures, the EAT ECU increases the converter lock-up control and modifies the shift
programme to reduce fluid temperature.
If the temperature sensor fails, the EAT ECU uses a programmed default temperature value. The default value is
derived from the engine coolant temperature sensor and received on the CAN from the ECM. A fault code is stored
in the ECM which can be retrieved using TestBook.
The temperature sensor has a semi-conductor material with resistance to temperature values as shown in the
following table.
Temperature Sensor Resistance Values
Temperature
Resistance
0
°
C (32
°
F)
820
Ω
20
°
C (68
°
F)
962
Ω
40
°
C (104
°
F)
1118
Ω
60
°
C (140
°
F)
1289
Ω
