Electric fan activation sensor
Examination
1. Sensor welding is described in paragraph 5, as part of the electric fan welding procedure.
Withdrawal
Note: The engine and radiator must be completely cool before removing the sensor.
2. The sensor is installed on the left side of the radiator. above the lower hose fitting, accessible from above on most models. Loosen the fixing screws and remove the lower motor protection cover so that the sensor is accessible from below.
3. Disconnect "mass" battery wire.
4. Drain the coolant up to the level of the sensor, as described in the relevant part chapter 1. Proceeding otherwise, prepare a suitable plug to install it immediately after unscrewing the sensor. In any way, try not to damage the radiator and do not allow foreign particles to enter it.
5. Disconnect the multi-pin connector from the fan switch.
6. Carefully unscrew the sensor from the radiator and remove the O-ring from it (if provided). Plug the hole to prevent fluid loss.
Installation
7. If the old sensor was installed with an o-ring, install a new one. If there was no O-ring, apply sealant to the threaded part of the sensor.
8. Installation - reverse procedure. Tighten the sensor to the specified torque and fill the system with coolant as described in the appropriate article chapter 1.
9. Finally, start the engine and warm it up to operating temperature. Check that the fan turns on in time.
Temperature indicator/emergency temperature indicator sensor
Examination
10. Not all models have the sensor installed in the cooling system outlet at the left rear of the cylinder head (pic. 6.10). If two sensors are installed, the outer of the two is the temperature gauge sensor (internal sensor - for BEU engine).
11. The temperature gauge receives stabilized power from the instrument panel (from the ignition switch through the fuse). Connecting the device with "weight" carried out through the sensor. The sensor contains a thermistor - an electronic element whose electrical resistance decreases according to a certain schedule with increasing temperature. If the temperature is low, the resistance of the sensor is high, the current through the pointer decreases, the arrow of the device deviates to blue (cold) scale sector. As the temperature rises, the reverse process occurs, the arrow creeps into the red sector. A defective sensor must be replaced.
12. The emergency temperature indicator is powered in the instrument panel. Negative terminal connected to "weight" through the sensor, which is essentially a bimetallic pair of contacts that close when the engine reaches an emergency temperature.
13. The sensors are mounted in one housing with a four-pin connector.
14. If a malfunction occurs in the panel, first check the supply voltage to all devices on the panel. If there is no voltage, or it is incorrect, the voltage regulator may be faulty, which in this case must be replaced (stabilizer - part of the instrument panel circuit board - see chapter 12). If the fault is only in the temperature gauge, carry out the following check.
15. If the gauge needle shows a low temperature all the time, although the engine is warm, disconnect the wiring connector from the sensor and attach it to "mass" - the metal part of the engine. With the ignition on, the arrow should move to the high temperature area on the device. If not, the defective sensor must be replaced. If the arrow does not move and when the connector is shorted to ground, remove the instrument panel as described in chapter 12 and check the condition of the circuit between the sensor connector and the device and the power supply to the device. If the circuit is working and voltage is supplied, the device is faulty and you need to lure it.
16. If the arrow of the device specifies high temperature at the cooled-down engine, disconnect a socket from the gauge. If at the same time the arrow returned to the lower temperature area with the ignition on, the sensor is faulty. If the arrow still moves, check the condition of the chain as described above.
17. This basic principle also underlies the verification of the emergency temperature indicator. The indicator should light up if the connector of its sensor is shorted to "mass".
Withdrawal
1S. Drain the coolant as described in chapter 1A or 1B. Proceeding otherwise, unscrew the expansion tank cap to relieve pressure in the system and keep a new sensor block or suitable plug on hand. If you use a plug, be careful not to damage the sensor opening or allow foreign particles to enter the system.
19. On diesel engines, remove the plugs, unscrew the fastening nuts and remove the engine top cover to get to the sensor.
20. Disconnect the multi-pin connector and determine whether the sensor is screwed in or inserted.
21. If the sensor is screwed, unscrew it from the engine and remove the sealing washer.
22 If the sensor is inserted, push it in and unhook the retainer. Remove the sensor and its O-ring from the engine.
Installation
23. If the sensor is screwing in, install a new O-ring, refit the sensor and tighten it securely.
24. If the sensor is inserted, replace the O-ring and insert the sensor with the retainer.
25. Connect the connector and fill the system as described in the relevant part chapter 1 or top up as described in weekly checks, on diesel engines, install the engine top cover.
Temperature sensor of the BEU of the engine
26. On all models, the sensor is installed in the outlet of the cooling system in the left rear of the cylinder head. If two sensors are installed, the outer of the two temperature gauge sensors (internal sensor - for BEU engine).
27. The sensor is a thermistor (see point 11). The ECU of the engine supplies the sensor with voltage by measuring the current passing through the sensor, calculating the temperature of the engine. Together with data from other sensors, the received information is processed and used to control the injection ignition timing, idle speed, diesel engine glow plugs, etc.
28. If the sensor circuit is broken, the BEU will switch to a spare mode of operation, the engine will continue to work, albeit with less efficiency. This will cause a warning light to come on in the instrument panel - consult your Audi/VAG dealer for advice. The sensor itself can only be checked using specialized equipment at a dealer car service. DO NOT attempt to test the sensor with other equipment, risking damage to the ECU.
Removal and installation
29. Refer to the information given in p.p. 18...25.
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