Knock Sensor: Testing and Inspection

Knock Sensor, Checking

The following procedure is used to diagnose all Knock Sensors.

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

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

Start diagnosis

- Remove the engine cover. Refer to the Repair Information.

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

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

Checking internal resistance

- Using a multimeter, check the Knock Sensor terminals 1 to 3 for an internal short.

Specified value: infinity (Infinity or OL reading).

If the specified value was Not obtained:

- Replace the shorted Knock Sensor (KS) 1 (G61)/Knock Sensor (KS) 2 (G66).

If the specified value was obtained:

Checking wiring

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

- Using a multimeter, Check the Knock Sensor electrical harness connector to the Motronic Engine Control Module (ECM) (J623) electrical harness connector T60 for an open circuit. Refer to Wiring Diagrams for pin locations.











Specified value: 1.5 ohms Max.

If the specified value was Not obtained:

- Check the wiring connection for an open circuit, short circuit to Battery (+) 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 sensor resistance was OK:

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

- Install the engine cover with air filter. Refer to the Repair Information.

Final procedures

After the repair work, the following work steps must be performed in the following 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 ] Monitors, Trips, Drive Cycles and Readiness Codes.