Table of contents: Malfunctions ↓ Checking the coolant temperature… ↓
The coolant temperature indicator works in much the same way as the fuel level indicator. Power is supplied to the device when the ignition is on, and the connection to ground is made via the temperature sensor on the engine (see illustrations). This sensor is a resistance that allows more current to pass through the higher the temperature, so the bimetal element in the device gets hotter, causing the needle to move further. Audi uses two different types of temperature sensors.
Standard sensor (combined with "overheat" switch for coolant temperature indicator), in 4-cylinder models without air conditioning.
Electronic thermal switch (has other functions too) in 4-cylinder models equipped with air conditioning, as well as in 5- and 6-cylinder models.
The location of the temperature sensor contacts is shown in the illustrations.
Hint: When the coolant temperature is high, a red flashing warning light or the "coolant" symbol will also come on.
Malfunctions
An inaccurate coolant temperature indicator and an inaccurate fuel level indicator indicate a damaged voltage stabilizer.
The reason for the completely absent indication may be both the temperature sensor and the device.
If the indicator is correct, but the indicator is also flashing, you should check the coolant level sensor located in the expansion tank.
Disconnect the temperature sensor plug in the engine compartment.
Checking the coolant temperature indicator
Use a piece of wire to extend the individual plug contact to the temperature indicator (brown-yellow wire) in a multi-pin plug (see also illustrations on the next page) and bring it to bare metal ("ground").
The location of the temperature sensor in a 4-cylinder engine. The numbers indicate:
1 — contact of the "coolant overheating" indicator;
2 - "mass" (body);
3 — coolant temperature indicator.
Vehicles with 4-cylinder engines use the same temperature sensor that you see in the illustration below in vehicles with 5- and 6-cylinder engines.
Turn on the ignition briefly.
If the previously stationary indicator needle now starts moving along the scale, this means the temperature sensor is faulty - replace it.
If nothing changes in the indicator, then there is a break in the wiring or a defect in the indicator itself. Its removal is described at the beginning of the chapter.
(The article was copied from the website «Audimanual.ru»)