Mercedes-Benz W202 diesel glow plugs and glow light
Mercedes-Benz W202 diesel: the glow light stays on long after starting or the car does not start cold, what is the fault?
Usually one or more glow plugs are dead, and the light tells you so. The alternatives are the glow relay or the fuse inside it; the relay is in the black box on top of the driver's side wing in the engine bay. Moisture and oxidation can cause the fault.
How do I check the Mercedes-Benz W202 diesel glow system?
Battery voltage is about 12.6 V before the current is switched on. During glowing it should drop to about 11 volts; if it stays at 12 volts or above, the glow plugs are not working. An individual plug can be tested with a headlight bulb connected in series, which must light up briskly.
How do I replace a glow plug without it breaking?
Remove the cover on top of the intake manifold, and all four plugs are visible. Replace a faulty one at once, since an old plug seizes in place and breaks easily. When one is dead, it is worth replacing the others too. Tighten correctly so that soot does not build up in the threads.