Where is the engine coolant temperature sensor in a 1997 Audi A6 Quattro and how do I replace it?

The 1997 Audi A6 Quattro has Two ECT (engine coolant temperature) Sensors. One is located on top of the engine just behind the coolant neck. The other is found on the left lower side of the radiator hose outlet on top of the transmission bell housing.

Here is how to replace the ECT sensor behind the coolant neck:

1. Disconnect the coolant hoses from the coolant neck. There are two hoses; you may need a spring clamp tool.

2. Remove the two bolts holding the coolant neck to the intake manifold.

3. Gently pry the coolant neck up and off. Be careful not to damage the O-ring.

4. Remove the old ECT sensor by grasping it with a pair of pliers and twisting counterclockwise.

5. Apply some thread sealer to the threads of the new ECT sensor and screw it in clockwise.

6. Reattach the coolant neck, O-ring and re-install the bolts.

7. Re-connect the coolant hoses and top up the coolant level.

Here is how to replace the Lower ECT Sensor on the Transmission Bell Housing:

1. Remove the engine undercover if equipped

2. Reach down along the transmission bell housing from the top using a combination wrench to loosen the ECT from the Coolant hose connector.

3. Unclip the wiring connector from the sensor housing.

4. Remove the sensor.

5. Apply Teflon sealant tape to the threads of the new sensor.

6. Install the new sensor.

7. Reattach the wiring connector.