20V Motronic ECU System

1991 200TQ and 1992-95 S4/S6 with 20V Turbo Engine:

Engine Timing Sensors, Reference and Engine Speed

There are two magnetic Inductive pickup sensors mounted on the rear portion of the engine block and are inserted into the bell housing near the flywheel.

The Engine Speed Sensor is mounted near the flywheel "starter" teeth to monitor engine RPM as the metal teeth pass by the sensor tip.

The Reference Sensor is mounted further inward near a pin that is pressed into the front side of the flywheel. Here is a view from the flywheel side with the transmission and flywheel removed.



This Reference pin is located on the flywheel to give the ECU a reference point that is 62 Degrees Before Top Dead Center (BTDC) for Cylinder #1.

NOTE: If either one of the sensors fail, the engine cannot be started, but, if the reference sensor fails while the engine is running, the system will use the #1 cylinder signal that was originally used when the engine was first started to allow the engine to keep running [1][2]

Some have found these sensors will fail intermittently when the engine is hot/warm, but work ok after cool down. These sensors are available if you find you have a defective sensor.


Please note that if you are interrogating the Engine Control Unit to check for any stored fault codes with the engine not running, the Engine Speed sensor may show up with a fault.

Return to 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
[2] "Motronic Engine Management System for the Audi S4 and the 4.2 Liter Audi V8" All rights reserved.

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