Mercedes E220CDi Glow Plug Warning

Valetta

Hi
I have a 2006 Mercedes E220CDI (170 BHP).

In the last couple of weeks, just after starting the engine, the Glow Plug warning light comes on. It stays on for about 15-20 seconds and then goes out. I have a couple of questions before bringing it to a garage:

a) As I understand it, glow plugs are used to heat the cylinder to make starting easier. However, on older diesel cars the light would come on as soon as the ignition is turned on, then go out to indicate the plugs had heated up and you would then start the engine. In my car up till now the light has never stayed on for more than a fraction of a second. Does this mean the glow plugs are an unnecessary component?

b) As the car is starting without any problems, what, if any are the implications of just ignoring the warning light?

Many thanks for any advice.

Slideways

The light on the CDI only comes on to indicate a faulty plug.
On the vans there was a plug away from the engine that you could unplug and do a resistance test to check which plugs and how many are faulty.

These have a habit of twisting off so a bit of caution is needed when taking them out

MercMad

The issue will be that one or more of the Glow Plugs has failed. You need to get the codes read to find which one. In my experience the failed plug will take out the relay also which has fusible links for each plug. You could be lucky and get away with one plug, but they are cheap enough so I tend to replace the set then open the relay and solder in a link.