Knock Sensor: Testing and Inspection

Diagnostic Procedures

Knock Sensors, Checking

Special tools, testers and auxiliary items required

• Multimeter.

• Wiring diagram.

Test requirements

• The mounting bolt of Knock Sensor (KS) 1 (G61)/Knock Sensor (KS) 2 (G66) tightened to 20 Nm.

• The Motronic Engine Control Module (ECM) (J623) fuses OK.





• Battery voltage at least 12.5 volts.

• All electrical consumers such as, lights and rear window defroster, switched off.

• Vehicles with automatic transmission, shift selector lever into position " P" or "N".

• A/C switched off.

• Ground connections between engine/transmission/chassis OK.

• Ignition switched off.

Test procedure

- Observe safety precautions. Refer to => [ Safety Precautions ] Safety Precautions

- Observe Clean Working Conditions. Refer to => [ Clean Working Conditions ] Clean Working Conditions

- Perform a preliminary check to verify the customers complaint. Refer to => [ Preliminary Check ] Preliminary Check.

Procedure

• Before disconnecting the Knock Sensor electrical harness connectors, mark the component location.

- Disconnect Knock Sensor (KS) 1 (G61) electrical harness connector- 1 - or Knock Sensor (KS) 2 (G66) electrical harness connector - 2 -.





Checking internal resistance

- Using a multimeter, check terminals 1 to 2 of both knock sensors for an internal short.





Specified value: infinite (Infinity).

If the specified value was not obtained:

- Replace the faulty Knock Sensor (KS) 1 (G61) or Knock Sensor (KS) 2 (G66).

If the specified value was obtained:

Checking wiring

If the manufacturers test box is being used. Perform the following step.

- Install the test box.

If the manufacturers test box is not being used. Perform the following step.

- Remove the Motronic Engine Control Module (ECM) (J623). Refer to the Repair Information.

- Using a multimeter, Check the knock sensor electrical harness connectors to the Motronic Engine Control Module (ECM) (J623) electrical harness connector T60 for an open circuit.













Specified value: 1.5 ohms Max.

If the specified value was not obtained:

- Check the wiring connection for an open circuit, high resistance or short circuit to voltage or ground.

- Check the wiring connection for damage, corrosion, loose or broken terminals.

- If necessary, repair the faulty wiring connection.

If no malfunction is found in the wiring and the resistance is OK:

- Replace the knock sensor that set the code.

- Erase the DTC memory. Refer to => [ Diagnostic Mode 04 - Erase DTC Memory ] Diagnostic Modes 01 - 09.

- Perform a road test to verify repair.

If the DTC does not return:

Generate readiness code. Refer to => [ Readiness Code ] Readiness Code.

If the DTC does return, no malfunction is detected in the wiring and the resistance is OK:

- Replace the Motronic Engine Control Module (ECM) (J623). Refer to the Repair Information.

- Assembly is performed in the reverse of the removal.

Final procedures

After repair work, the following work steps must be performed in the mentioned sequence:

1. Check the DTC memory. Refer to => [ Diagnostic Mode 03 - Read DTC Memory ] Diagnostic Modes 01 - 09.

2. If necessary, erase the DTC memory. Refer to => [ Diagnostic Mode 04 - Erase DTC Memory ] Diagnostic Modes 01 - 09.

3. If the DTC memory was erased, generate readiness code. Refer to => [ Readiness Code ] Readiness Code.