Coolant temperature gauge

The ambient temperature sensor (arrow) is located in the bumper on the left, behind the radiator grille.

Left: under the injection system temperature sensor (2) on models with the 5-cylinder engine is the electronic thermal switch (1). The terminal layout is as follows:

T – temperature gauge;
R – air conditioning;
+ – power supply;
C – warning lamp "coolant overheating".

Right: models with the 6-cylinder engine have the same electronic thermal switch (arrow) with an identical terminal layout. It is screwed into the coolant line at the rear right of the engine.

The coolant temperature gauge works in much the same way as the fuel level gauge. Power is supplied to the instrument with the ignition on, and the ground connection is made through the temperature sensor on the engine. This sensor is a resistance that passes more current the higher the temperature, so the bimetallic element in the instrument heats up more and the needle deflects further. Audi uses two different types of temperature sensors.

Standard sensor (combined with the overheating switch for the coolant temperature warning lamp). Fitted to models with the 4-cylinder engine without air conditioning.

Electronic thermal switch (with additional functions) on models with the 4-cylinder engine with air conditioning, and on models with the 5- and 6-cylinder engine.

The terminal layout of the temperature sensor is shown in the illustrations.

Note: if the coolant temperature is too high, the red flashing warning lamp also illuminates. On vehicles equipped with a self-diagnosis system, the "coolant" symbol appears.

Malfunctions
An inaccurate coolant temperature gauge reading together with an inaccurate fuel gauge reading indicates a faulty voltage stabilizer.

A completely absent reading may be caused by either the temperature sensor or the instrument.

If the reading is correct but the warning lamp flashes at the same time, check the coolant level sensor located in the expansion tank.

Checking the coolant temperature gauge
PROCEDURE

Disconnect the temperature sensor connector in the engine compartment.

Using a piece of wire, extend the separate connector terminal to the temperature gauge (blue-brown wire) in the multi-pin connector and connect it to bare metal (ground).

Switch the ignition on briefly: if the gauge needle, which was previously stationary, now moves across the scale, the temperature sensor is faulty and must be replaced.

If nothing changes in the gauge, there is a break in the wiring or the gauge itself is faulty. Its removal is described at the beginning of this chapter.