The relay guarantees the current supply time of candles and controls the value of the current voltage. This relay has a special electronic unit (to be heated up to 1300 degrees Celsius, the candles consume from 8 to 40 each). On board a spiral light is enlightened that announces the driver who must return the appetizer until he turns off. For the most recent car models, everything is electronically monitored, announcing the engine temperature and, if it is quite hot, the candles will not light up.

The ignition can fail for two reasons, that is to say:
- The relay is worn (this happens after 75,000 -100,000 km of running)
- Fuel fuel supply equipment.
Before starting the diagnosis of the Diesel preheating system, it is necessary to inform which thermal conditions heated the combustion room of the equipment and also what kind of candles, because there are two construction types:
- With auction (the heating element is made in a refractory metal spiral)
- For ceramic article (the heater is a ceramic powder)
Symptoms that recall the problems can report:
- White gray smoke at the start: this can announce that it is fuel, but it is not correct
- Go defective
- The engine does not start: the relay controls the fuel power; If the car does not receive fuel, obviously it will not start
- The engine dies immediately after the start
- Sometimes it starts, sometimes not – sometimes the relay works, sometimes
- The car does not start, even if the interior is hot: the connections that provide the relay are dislocated
- Hard operation of the cold engine in the ranks
- The engine trembles at the beginning – because the mixture of some cylinders lights up late
Causes symptoms for incandescent candles of oscillating relay:
- The candle partially destroyed the tip
- Thick carbon deposits in the upper part
- Deformation of the candle due to overvoltage
- The relay contacts oxidation due to the lack of sealing the housing and the penetration of humidity. The oxidation of contacts leads to a heavy start of the engine (or may not start at all, depending on the degree of oxidation)
Nr | Symptoms of defective relay | Car model |
1 |
|
Opel Astra H. |
2 |
|
BMW |
3 |
|
Renault Megane 1.5 DCI |
3 |
|
Citroen c4 |
4 |
|
Mercedes Benz |
5 |
|
Dacia Logan McV 1.5dci |
6 |
|
Volkswagen Golf 4 1.9 TDI |
Depending on the constructive version, access to the relay is easy or more difficult. Sometimes you can change it alone, but most of the time the witness of the error will appear on board, which will not disappear and will also have to be deleted with a specialist, who will charge the same rate, so we recommend replacing it for a service.
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