Test conditions: engine cold (has the same temperature as the air) the battery is charged and its voltage is at least 11.5 V.
Checking the power supply
This check can be performed without removing the glow plugs.
1. Remove the engine protection, see the relevant chapter.
2. Connect a power test light in parallel to the glow plug supply wire and to the ground (-).
3. Turn on the ignition and warm up the engine. Observe the indicator light while holding the key in the ignition switch in the preheating position. The light should come on and go out a few seconds after the preheating is complete.
(Article based on data from the website: MercedesMan.ru)
4. Connect the glow plug power wires.
Checking the spark plugs
5. Disconnect the glow plug power wires.
6. Measure the resistance of each spark plug with an ohmmeter by connecting the ohmmeter to the spark plug and to the ground (-) of the vehicle.
If the device does not register the presence of resistance (0 Ohm), then the spark plug is faulty and must be replaced.
7. Connect the glow plug power wires.
8. Install the engine protection back in place, see the relevant chapter.