20V Motronic ECU System

1991 200TQ and 1992-95 S4/S6 with 5 Cylinder 20V Engine

KNOCK SENSOR Intermittent Operation? Hesitation? Low Power?

It is possible that the ECU is detecting a fault in the knock sensor system caused by a loose, defective or intermittent knock sensor(s). Abnormal engine noises, knocking, lifter clacking, loose mounting brackets etc, may also fool the knock sensor into thinking the engine is pinging.

The mounting torque of the knock sensor is critical to correct operation and should be checked, the 3B and AAN engines use two knock sensors that should be torqued to 15 lb-ft.

1991 200TQ 20V with 3B engine
The newer style replacement knock sensors have gold plated terminals and the wiring harness connector terminal pins should be replaced with these gold plated versions as well. Some of the 1991 200TQ's have the "Check Engine" light bulb removed from the dash, so if the car is having a problem with one or both of the knock sensors, you may not know it.

The "Check Engine" light should come on with the ignition key turned on to the first position. NOTE: The ECU will retard the timing 6 degrees if it thinks one or both of the knock sensors are not working [1]. Sensor #1 is for Cylinders 1,2 3. Sensor #2 is for cylinders 4 and 5.

This can make the car stumble or hesitate on acceleration. Check for any stored fault codes NOTE: A defective pressure sensor inside the ECU may also cause the "Check Engine" light to come on and the engine may have excessive pinging.

The hose from the intake manifold to the ECU should be checked for leaks as well.

Audi parts on-line catalog

20V ECU system information index

References: [1] Audi of America, Technical service training publication:
"The New 20V Turbo Engine for the Audi 200 Quattro-publication All rights reserved.

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