Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
Knock Sensor, Checking
This procedure is used to diagnose Knock Sensor (KS) 1 -G61- and Knock Sensor (KS) 2 -G66-.
Special tools and workshop equipment required
- Multimeter
- wiring diagram
Cylinders 1, 2 are monitored by Knock sensor (KS) 1 --G61--. Cylinders 3, 4 are monitored by Knock sensor (KS) 2 --G66--.
Knock sensors themselves cannot be checked electrically.
When servicing terminals in the harness connector of knock sensors, use only gold-plated terminals.
For the knock sensors to function properly, it is important that the tightening torque be exactly 20 Nm.
Contact surfaces between Knock Sensor (KS) 1 -G61- and Knock Sensor (KS) 2 -G66- and cylinder block must be free of corrosion, dirt and grease.
Test requirements
- Mounting bolt of Knock Sensor (KS) 1 -G61- /Knock Sensor (KS) 2 -G66- tightened to 20 Nm.
- Fuses for Engine Control Module (ECM) -J623- OK refer to appropriate SYSTEM WIRING DIAGRAMS.
- 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 PRELIMINARY CHECK .
Start diagnosis
-- Pull engine cover out of first mount at front arrow 1, then at right rear arrow 2 and finally at left rear arrow 3.
-- Disconnect the electrical harness connector from Knock Sensor (KS) 1 -G61- -1- or the electrical harness connector from Knock Sensor (KS) 2 -G66- -2-.
-- Using a Multimeter, check Knock Sensor (KS) 1 -G61- or Knock Sensor (KS) 2 -G66- component terminals 1+2 for a short to each other.
Specified value: ∞ (No Continuity).
If the specification is not obtained:
-- Replace the faulty Knock Sensor --. Refer to KNOCK SENSOR OVERVIEW .
If the specification is obtained:
If the manufacturers test box is being used. Perform the following step.
-- Install the Adapter Cable (121 Pin) VAG 1598/31.
-- Using a Multimeter, check the following wiring connections for an open circuit.
| Knock Sensor 1 -G61- electrical harness connector terminal | Motronic Engine Control Module (ECM) -J623- electrical connector T121 terminal or test box socket |
|---|---|
| 1 | 106 |
| 2 | 99 |
| 3 | 108 |
| Knock Sensor 2 -G66- electrical harness connector terminal | Motronic Engine Control Module (ECM) -J623- electrical connector T121 terminal or test box socket |
|---|---|
| 1 | 107 |
| 2 | 99 |
| 3 | 108 |
Specified resistance 1.5 Ω max.
-- Check the wiring for a short circuit to Battery positive (+) or an open circuit.
-- If necessary, repair the wiring connection.
-- Erase the DTC memory. Refer to DIAGNOSTIC MODE 04 - ERASE DTC MEMORY .
-- Perform a road test to verify repair.
If the DTC does not return:
Repair complete, Generate readiness code. Refer to READINESS CODE .
-- End diagnosis.
If the DTC does return and no malfunction is detected in the wiring and the voltage supply was OK:
-- Replace the Motronic Engine Control Module (ECM) -J623-. Refer to MOTRONIC ENGINE CONTROL MODULE, REPLACING .
-- Assembly is performed in the reverse of the removal.
Final procedures
After the repair work, the following work steps must be performed in the following sequence:
- Check the DTC memory. Refer to DIAGNOSTIC MODE 03 - READ DTC MEMORY .
- If necessary, erase the DTC memory. Refer to DIAGNOSTIC MODE 04 - ERASE DTC MEMORY .
- If the DTC memory was erased, generate readiness code. Refer to READINESS CODE, SETTING .
End of Diagnosis.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.
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