290GD glow plug light

If the symptoms are as follows:

Glowplug light won't come on until you star the engine and then stay on for about one minute...

then one or more glowplugs are faulty.

If glowplug light won't come on until you star the engine and then stay on forever, it's the glowplugs relay the one which is faulty.

I had the first problem when I bought my G three years ago and decided having all six glowplugs (OM603) replaced. Then last friday I had the same problem again, after only 28,000 kms (17,500 miles). I had all glowplugs tested and found that the one in the six cylinder was faulty. This was lucky because I could replace it without having to remove the inlet manifold and fuel lines which is a PITA!

If you don't know when were your glowplugs replaced, I would advise changing them all (you have five in your OM602 engine). Cost in any Bosch distributor is very affordable (I paid just 8 pounds for one with a 35% discount on the list price). This is the best solution if you don't have the equipment to tell which one is faulty. Also if the faulty one(s) is/are in the middle cylinders you will have to remove the inlet manifold and fuel lines and given the hassle and/or the labour cost, it's better to replace them all.

Cheers