Our AAN engine ECU uses signals from two separate piezo-electric knock sensors to help control and adjust ignition timing, etc. to prevent pinging (pinking in UK-speak). Here's what VAG says:





Here is where they live (under the intake manifold):

The part numbers are shown in this diagram (Item 12), one green one, one blue one. They connect to the ECU harness at the firewall connector rack.


If there are problems, you might get at check engine light (CEL) with these codes:

*2141 (Blink Fault Code), 00535 VAG1551/2 Fault Code Number
Knock regulator #1
Excessive knock, timing is being retarded by maximum amount,
Symptom: Low boost on 20V, Fuel octane too low, Excessive Compression, excessive boost

*2142 (Blink Fault Code), 00524 VAG1551/2 Fault Code Number
Knock sensor #1 (G61)
Open or short circuit, Defective sensor Check sensor and wiring
Symptom: Timing retarded, High fuel consumption, power loss, Boost pressure not attained

*2143 (Blink Fault Code),00536 VAG1551/2 Fault Code Number
Knock sensor #2, (Cylinders 3, 4, 5)
Excessive knock, timing is being retarded by maximum amount.
Symptom: Fuel octane too low, Excessive Compression, excessive boost

*2144 (Blink Fault Code), 00540 VAG1551/2 Fault Code Number
Knock Sensor #2, (G66) (Cylinders 3, 4, 5)
Open or short circuit, Defective sensor or wiring
Symptom: Timing retarded, High fuel consumption, power loss, Boost pressure not attained
(Reference SJM Autotechnik)

This will be on the exam.