This is a diagnostic mode. The car is telling you it has a burned out glow plug. The glow plug relay measures the resistance of the plugs - it is finding something it doesn't like - probably infinite resistance in one plug.

The car will still start and run just fine with one plug out. If you pay attention, you'll probably notice following the first cold start of the day the car runs a bit rough and smokes a bit much for the first few seconds. It's pretty much running on four cylinders until the fifth heats up enough the reliably ignite the fuel.

If you have all original glow plugs, your best option is probably to replace them all. They're not expensive - about $15/each from mail order vendors, nor are they difficult to replace. I'd also recommend replacing the 80 amp strip fuse inside the glow plug relay. They too occasionally fail due to age. It's available at your local MB dealer for a buck or so.

You'll be good for another ten years after this service.

- Jim