20V Motronic ECU System

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

MULTI-FUNCTION TEMPERATURE SENSOR (MFTS) Intermittent operation? Defective?

One additional sensor to check when having low boost problems on the 1991 200TQ 20V, is the Multi-function Temperature sensor which is mounted underneath the intake manifold on the coolant pipe on the side of the cylinder head. It uses a 4 terminal connector which is normally is covered with a protective rubber boot.

The 1991 200TQ 20V and 1992-95 S4/S6 Engines use the same Multi-Function sensor as the 5000/200TQ etc. but it is mounted upside down on the water pipe that connects to the upper radiator hose.


1991 200TQ 20V Location

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1992-95 S4/S6 Location

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Look underneath the intake manifold to locate this sensor. The newer style replacement Multi-Function Temperature Sensors will have only 3 terminals as they simplified the internal design of this sensor and eliminated the +12V supply to this sensor.

1991 200TQ 20V: Unfortunately, the 3 terminal version may fail with a "false" overheat signal which will shut off the A/C compressor and send a signal to the 1991 200TQ 20V ECU to lower the boost.

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The 1992-95 S4/S6 Engine Control Unit does not use this Multi-Function Temperature Sensor input and will not experience low boost problems from its failure.

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Located in the Body Electrical section of our catalog as the "Water Temperature Sender"

This MFTS temperature sensor supplies the signal for the dash mounted coolant temperature gauge and can cause intermittent temp gauge operation. In some cases the connector terminals can be corroded and will be causing a poor connection.

If the connections are ok, then the sensor is likely defective inside and is causing this intermittent coolant temp. gauge operation. It is very common for the gauge to begin working after this 4 pin connector is removed and installed due to internal sensor connections being moved.

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1991 200TQ 20V:
This MFTS sensor also provides a ground signal from Pin 2 on the sensor to PIN 36 on the Motronic ECU (J220) if the engine is running too hot (over 247F, 119C) which will reduce the amount of boost the ECU will provide.

The Waste Gate (WG) operation is not allowed when this overtemp condition occurs. The BL/G wire (2/R terminal) coming from this sensor should be tested to ensure that it is not grounded. If you remove the connector from the Multi-function temp sensor, pin 2 is the one on the lower right, with the connector end facing you and the connector notch towards the top.

If you suspect the Multi-function sensor is causing the low boost, you should remove the connector from the Multi-function switch and redo the test.

If it works with the connector removed from the Multi-function temp sensor, then the temp sensor is defective and is grounding Pin 2 which will prevent correct operation and this will limit turbo boost output. You should check the wiring between the throttle switch and the ECU as well.

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ALL 20V Turbo

This wire from Pin 2 on the sensor, is also routed to the A/C control head unit which will turn off the A/C if the engine temp. exceeds 247F. The sensor is also connected to the dash mounted warning system and will issue a warning symbol if the engine coolant temp exceeds 247F [1].

I have some additional information on this "wonderful" multi-mal-function sensor in the cooling system

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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