It is impossible to check the control unit using the devices available to the motorist. This can only be done by a workshop. On the assumption that the preheating system is faulty, the motorist can check it himself by following the steps below.
1. Check control box fuses 21 and 27.
2. Check the 80A fuse.
3. Open the cover of the central distribution box and check that the fuse link has not oxidized or burned out. Replace defective insert.
4. Check the voltage supply to the candles, if the fuse is OK.
5. Remove the tip of the power wire of one of the candles (see illustration).
6. Connect one tester wire with a control diode bulb to the removed spark plug power wire, and the second tester wire to «mass» (-).
7. Disconnect the coolant temperature sensor connector.
8. Turn the key in the ignition switch to position «warm up». The tester's diode lamp should light up and remain in this state for about 28 seconds. In this case, the power supply to the glow plugs and the control of the duration of the warm-up are normal. The indicator light on the instrument panel goes out after about 20 seconds. If the tester's diode lamp does not light up, then the fuse is blown or the relay is faulty. If the time parameters for the duration of the warm-up are violated, then the reason for this is a malfunction of the control unit.
Open the cover of the central distribution box and check the relay. It is located in block number 12.
To check the glow plug itself, it must be removed.
9. Remove all glow plugs and place on a refractory pad. Before that, remove the tips of the candles and unscrew them with a socket wrench by 10 (see illustration)
10. Connect the spark plugs using auxiliary wires with a cross section of at least 2.5 mm directly to the battery. Watch the candles to determine which one is not working or glowing weakly.
11. Replace defective spark plugs. It is recommended to change all candles. The moment of an inhaling of candles is 15 Nm.
On AUDI 80 vehicles with a TDI engine, glow plugs of the following names are installed:
- Beru 725 MJ;
- Rosch, N2 article 0250 202 009;
- Audi article no. 101 40101.
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