Knock Sensors, Checking

The following procedure is used to diagnose all Knock Sensors --.

Special tools and workshop equipment 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) - J220- fuses OK.
  Fig 1: Identifying Fuses On E-Box In Engine Compartment, Left Side

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• 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 (GND) connections between engine/transmission/chassis OK.
• Ignition switched off.

Test procedure

-- Perform a preliminary check to verify the customers complaint. Refer to GENERAL DIAGNOSIS .

Start diagnosis

-- Remove the engine cover with air filter.

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

Fig 2: Identifying Electrical Harness Connectors

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Checking internal resistance

-- Using a Multimeter, check the Knock Sensor -- terminals 1 to 2 for an internal short.

Fig 3: Identifying Engine Speed (RPM) Sensor G28 Terminals

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Specified value: ∞ (Infinity).

If the specified value was not obtained:

-- Replace the faulty Knock Sensor (KS) 1 -G61- /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. Refer to Repair information.

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

-- Remove the Motronic Engine Control Module (ECM) -J220-. Refer to MOTRONIC ENGINE CONTROL MODULE, REPLACING .

-- Using a Multimeter, Check the Knock Sensor -- electrical harness connector to the Motronic Engine Control Module (ECM) J220 electrical harness connector T121 for an open circuit.

Fig 4: Identifying 3-Pin Connector

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Specified value: 1.5 Ω Max.

If the specified value was not obtained:

-- Check the wiring connection for an open circuit, short circuit to Battery (+) or Ground (GND).

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

-- If necessary, repair the faulty wiring connection.

If no malfunction is found in the wiring and the resistance was not OK:

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

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

-- Replace the Motronic Engine Control Module (ECM) -J220-. Refer to MOTRONIC ENGINE CONTROL MODULE, REPLACING .

-- Install the engine cover with air filter.

Final procedures

After 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 .
2. If necessary, erase the DTC memory. Refer to DIAGNOSTIC MODE 04 - ERASE DTC MEMORY .
3. If the DTC memory was erased, generate readiness code. Refer to READINESS CODE .

-- End of diagnosis.