Heating & Ventilation, A/C

B2355

Evaporator temperature sensor. Shorting to ground
Evaporator temperature sensor. Open circuit/short to B+
Evaporator temperature sensor. Out of range





Fault symptoms
Temperature sensor in evaporator stops functioning, which means that the A/C system does not supply cold air.

Diagnostic help
The evaporator temperature can be read on the diagnostic tool.

A reference resistor is useful when diagnosing a faulty sensor. This would give the following readings on the diagnostic tool:
- 6.2 kohm gives approx. 20 °C
- and 11 kohm gives approx. 8 °C.

See Evaporator Temperature Sensor, "Application and ID" for the association between temperature and resistance.
Evaporator Temperature Sensor / Switch





Diagnostic procedure

1. Checking the sensor's ground connection
- Unplug the connector: Temperature sensor, evaporator A/C: (621).





- Connect test lamp 86 11 857 between B+ and pin 2 on the female connector.
- The test lamp should light.

Is the function correct?
YES
- Go to step 2.
NO
- Rectify open circuit/short circuit to B+ in lead between pin 2 on the sensor connector and pin 30 on the control module connector.
- Go to step 3.





2. Checking the signal input on the control module
- Turn the ignition key to ON





- Measure the voltage
- Red test lead:
Temperature sensor, evaporator A/C:1.
- Black test lead:
Temperature sensor, evaporator A/C:2.
- Value should be 6.5V - 8.5V.

Is the function correct?
YES
- Replace: Temperature sensor, evaporator A/C.
- Go to step 3.
NO
- Rectify faulty lead between pin 1 on the sensor connector and pin 10 on the control module connector.
- Go to step 3.





3. Final check
- Delete diagnostic trouble codes in all Systems.





- Carry out a function check.
- Evaluate the function check.





- Check that the diagnostic trouble code does not recur.

Does the diagnostic trouble code recur?
YES
- See "Before changing a control module." Before Changing a Control Module

NO
- The steps taken to rectify the fault were correct.