I was working on the brakes on this e300d yesterday and drove it around. Today the glow plug light that comes when starting and turns off when its ready to start does not come on at all. The car turns over but will not fire. Anyone have a clue? Did I trip something while bleeding the brakes?

If the glow indicator light does not light, one or more glow plugs are defective, the glow plug relay is defective, or maybe (I just don't remember) a 30A fuse is blown.

No light on means no current to glow plugs means diesel no start. It might start if you crank for long time depending on the air temperature, but that's hard on the starter.

The glow plugs are about a year old so I dont think it is that. I will check the other items. Thanks

I dont get it. Put an OBD2 scanner on the car and no codes came up then attempted to start the car and it started right up. For two days nothing and I didnt touch anything on the car and today it starts no problem???

does the light still not work? find relay and check 30A fuse as suggested...also check relay terminals and such for voltage & continuity...

have friend turn key on while you listen to relay for a click

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1987 300TDT
1981 VW MKI Caddy 1.6 diesel, waiting on engine swap
1983 D-50 Power Ram 4x4 "Mitsubishi" 2.3 turbo diesel
assorted gas powered crap and motorcycles

RIP: 1984 300TDT, 1982 300TDT, 1984 190D 2.2, 1992 300D 2.5, 1987 300TDT, 1982 Maxima LD28, 1983 Maxima LD28, Isuzu C223 P'ups X3, 1983 Holiday Rambler 6.2 Banks turbo diesel, 1984 Winnebago LeSharo 2.1 TD, 1985 Allegro 6.5

IIRC there is a 15amp fuse on top of the K40 relay in the computer box that could be at fault. The fact that it is an intermittent problem now suggest the K40 relay itself might be the problem.

When was it last changed?

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Terry Allison
N. Calif. & Boca Chica, Panama

09' E320 Bluetec 77k (USA)
09' Hyundai Santa Fe Diesel 48k (S.A.)

I have had the car for 30 months and 55K miles and have not replaced anything but the fuel lines, glo plugs, brakes, and ball joint. Was not aware that the K40 relay is a maintainace item.

The PCB in the relay gets minute cracks in the circut pathways from continous exposure to heat. Causes lots of intermittent type electrical problems as it expands and contracts and current is interrupted. Most common K40 fault is the SOV closing while driving causing the engine to shut down instantly. Loss of power also prevents codes from registering in the ECU.

I'd guess most of them don't last for longer than 5-8 years typcially.

Some folks claim they can see the cracks with a good magnifying glass.

Something to keep in mind if you cant find something else causing the problem.

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Terry Allison
N. Calif. & Boca Chica, Panama

09' E320 Bluetec 77k (USA)
09' Hyundai Santa Fe Diesel 48k (S.A.)

Exactly the same! Under hood fuse is OK. Where is the glow plug relay located?

LFB - The GP relay is on the drivers side fender well next tot he ABS. The K40 relay is the front most relay inside the computer box on the pass side.

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Terry Allison
N. Calif. & Boca Chica, Panama

09' E320 Bluetec 77k (USA)
09' Hyundai Santa Fe Diesel 48k (S.A.)