If the control lamp does not light up when the engine is cold:
Pull out the glow plug relay (see pictures).
Disconnect the mounting plate together with the fuse holder; terminal "L" in the relay socket, connect to ground with a wire.
Turn the ignition key to position 1 and observe the pre-glow indicator lamp.
If it is lit, then there is a defect in the pre-glow relay or in the engine temperature sensor.
If it does not light up, then the light bulb with a glass base is defective or a defect in the light diode (in models manufactured after August 1980). Then a replacement should be made. See section "Devices".
Another possible malfunction is an interrupted power line.
Check relays manufactured before July 1977: remove the red-white wire of the engine temperature sensor; insulated or so secured in the engine compartment so that it does not come into contact with "weight".
Turn the ignition key to the 1st position and observe the pre-glow indicator light - it should turn on after about 1 minute. go out.
Turn the ignition key to position "Aus" ("Off") and then back to 1st position. The control lamp lights up again.
Now hold the red-white wire near the ground, the light goes out.
If the above test conditions are not met, then the glow plug relay is defective.
Otherwise, the engine temperature sensor must be changed.
Check relays manufactured after August 1977: unscrew the positive wire from the contact bar and insulate it.
Remove the wire from the engine temperature sensor and insulate. Or so strengthen the wire in the engine compartment so that there is no contact with "weight".
Turn the ignition key to the 1st position.
The pre-glow indicator light should now light up for about 1 minute. (maximum 2 min.) and then turn off.
Turn the ignition key back and then back to the 1st position
Now hold the wire of the engine temperature sensor at "masses"; the control lamp will go out immediately.
If the bulb does not light up as indicated above, the preglow relay is defective.
If it is on, there is a defect in the engine temperature sensor.
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