Fault Diagnosis (Volkswagen 16-Valve)

Connect voltmeter positive lead to positive post of battery. Connect voltmeter negative lead to single Blue/Brown or Brown/Blue wire connector in engine compartment (pin No. 4 of knock control unit). Turn ignition on. Voltmeter should indicate near battery voltage. Start engine. Voltage on meter should drop (a slight voltage signal may remain).
Accelerate engine to 3000 RPM (one time only). If voltage remains near zero volts, test is completed. If higher voltage signal returns, a knock fault has been detected. Connect a jumper wire to Blue/Brown connector. Hold jumper to ground for a minimum of 3 seconds and then remove. Voltmeter should start pulsing at this time.
If meter pulses in a pattern of 2 per interval, the knock sensor control unit or knock sensor circuit is faulty. Check knock sensor torque. Check for open or short circuit in knock sensor wiring. If knock sensor torque is correct and wiring is okay, knock sensor is defective. Connect ohmmeter across connector to knock sensor. Resistance should measure 300,000 ohms on type-1 knock sensor. Resistance should measure infinity on type-2 knock sensor.
If meter pulses in a pattern of 3 per interval, fault exists in pressure sensor (vacuum) circuit. Check White vacuum hose to knock sensor control unit for damage. If no faults are found, internal pressure sensor in knock unit is faulty.