Checking the knock sensor (VW Polo 3)

1. Connect the VAG 1598/18 tester to the engine control unit wiring harness (fig. 3.34).

2. Check the wires and the knock sensor for short circuit: sockets 19 and 39, 39 and 45, 19 and 45. Specification resistance: ∞ Ohms.

3. If no short circuit is found, remove the starter.

4. Disconnect wiring connector 1 from knock sensor 2 (Fig. 3.46).



5. Check the wires between the tester and the knock sensor for open circuit: pin 1 + socket 39, pin 2 + socket 19 Wire resistance: max. 1.5 Ohm.

7. Additionally check the resistance of the knock sensor contacts. Specific resistance: ∞ Ohm.

8. If no faults are found in the wiring, loosen the knock sensor fasteners and tighten it again to 20 Nm.

9. Install the starter.

10. Perform a test run. The following conditions must be met throughout the test:

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• the coolant temperature should not be higher than 80°C;
• after reaching the required temperature, perform the following modes: idle, partial load, full load. In full load mode, the rotation speed should be higher than 3500 rpm.

11. Read the fault memory again.

12. If no fault is found, replace the knock sensor.