Checking the coolant temperature sensor (VW Polo 3)

During self-diagnosis, the fault code "00522 Coolant temperature sensor" was detected.

1. Disconnect the 4-pin wiring connector 1 from the coolant temperature sensor 2 (Fig. 3.35).



2. Measure the resistance between contacts 1 and 3 of the sensor.

3. The set value is shown in Fig. 3.36. Area A shows the resistance in the temperature range of 0-50°C, area B shows the resistance in the temperature range of 50-100°C. For example, a temperature of 30°C corresponds to a resistance of 1500-2000 Ohm; temperature 80°C corresponds to resistance 275-375 Ohm.



4. If the specified value is not achieved, replace sensor 2.

5. If the specified value is reached, connect the VAG 1598/30 tester to the engine control unit wiring harness. Check the wires between the tester and the 4-pin connector for interruption of the circuit: contact 1 + socket 17, contact 3 + socket 42 (fig. 3.34). Specified value: max. 1.5 Ohm.



6. Additionally, check the wires for short circuits to each other, to the vehicle ground, and to the positive terminal of the battery.

Specification resistance: ∞ Ohm.

7. If no fault is found in the wires, then replace the engine control unit.

Additional check for a fault recorded as "Sporadic S/P fault".

8. If the fault code is stored in the memory as "Sporadic S/P fault": additionally check the sensor for functionality. To do this, the engine must be cold.

9. Connect the VAG 1551 tester and dial "01" to select the "Address word" function of the engine control unit. The engine should be idling. The display should show the following information:


10. Press "08" to select the "Read measured value block" function and confirm by pressing the "Q" button. The display should show the following information:


11. Press "001" to select the "Display Group 1" function and press "Q". The display should show the following information:



12. Check the value in field 2 with the engine running. The temperature should rise smoothly without delays.

• If the value on the tester display jumps from 2 to 5°C, this is caused by the control unit and not a sensor malfunction.
• If in some temperature ranges there are interruptions in engine operation and the coolant temperature does not increase smoothly, but intermittently, this means that there is a loss of signal and the sensor must be replaced.

13. Click "→".

14. Press "06" to select the "Complete Output" function and confirm by pressing the "Q" button.