Advise wanted.
Glow plug indicator clears after about 5 secs as per normal,
I then start the engine with no problems but then after approx
5 seconds the glow lamp indicator lights up again for anything
between 30 & 90 seconds before going out again whilst driving.
As the car is only 30 months old it has been repaired under warrenty but this is now the 3rd time it has happened.
Each time so far the garage has said that a timer has failed.
The first time the timer was replaced, the 2nd time the timer was replaced along with ONE glow plug that it had burnt out.
I've contacted the garage again and they state it can just be the
glow plug itself.
I'm a bit wary of this as i would have thought that once the lamp
went off after initial 5 secs this proved all plugs ok but after lamp
goes back on this proves fault lies elsewhere....Any ideas..

Sounds like the relay is detecting a burned out glowplug. This is pretty typical behavior of MB diesels for the last 20+ years. One caveat, though. We've never received the CDI engines over here on the left hand side of the Atlantic, so we have no direct experience with them. On my 1998 E300 turbodiesel (with OM606 engine) a failed glowplug typically caused the glow light to turn back on, and stay lighted, the "Check Engine" MIL would light, and a message would be displayed in the dash display. Difficult to miss it all.

Glowplug life on the OM606 engine is much shorter than previous MB diesels, perhaps this is true of the CDI engines as well?

- JimY

In the CDI's during the afterglow stage (after engine start) a
glow plug can become "open" after being heated for 10+ seconds
then the glow relay will detect this and activate the glow light
as a warning. Usually the check engine electronics signal will
activate as well.
You might want to start with a complete new set of plugs
instead of one at a time.
Good Luck.
DR.D