PeachParts Mercedes-Benz Forum - View Single Post

jay_bob · #5 10-25-2015, 10:03 AM

Your engine needs fuel and a little heat to get it going.

Fuel in this engine is delivered by the injection pump. On the year/model you have (W210 with an OM606 engine) the fuel supply to the injection pump is electrically controlled by a shut off valve. Also the fuel quantity is determined by the computer. A pedal sensor measures how much you push and the computer tells the injection pump how much fuel to deliver. These all depend on the K40 relay to deliver conditioned power to the electronics. There are, as you have experienced, issues with the K40, mostly related to cold solder joints.

A Diesel engine also needs a little heat on a cold start, to get the air hot enough to cause ignition of the fuel. This is provided by the glow plugs. The glow plugs are regulated by the glow plug relay. It is nearly impossible to get a cold Diesel engine to fire without that initial heat from the glow plugs.

In the older models, the relay was a rather simple arrangement that took a signal from the key switch to start a timer to apply power to the plugs. The dash light was set up to provide a prompt for the operator when to go ahead and crank and also advise if one or more plugs have failed.

In your W210 they started putting all the electronics on CAN bus. Think of it like a network in your car that ties all the various devices together. The glow plug relay in the W210, instead of having a direct connection to the switch, sits on the CAN bus.

The connector that puts the glow plug relay on the CAN bus can be problematic. I believe our fellow member tjts1 has had this problem, he has the same car as yours.