E class 2002 heater plug light

[The Duke]

Hi Guys. I have a 2002 E class. when I switch on the heaterplug light is on. start the car and the light goes out but shortly afterwards the light comes on and stays on. I have replaced the heater plug relay but the problem still remains. any ideas please. thanks. Phil.

 

[V6Matty]

when you say heater plug are you talking about the glow plugs on the engine? i would guess if yes that you have a dead glow plug that needs replacing. car will run fine without it but better to get it sorted sooner rather than later.

 

[The Duke]

Hi and thanks for your reply. I did have the glow plugs checked and they were said to be fine and was told that it must be a faulty relay. I replaced the relay but its still the same! Initally the glow plug light goes out after a few seconds as it should but sometimes it comes back on after a minute or two and then stay on all day and sometimes it dosent and stays off all day.
This is mind boggleing but if you could shine some light on it, that would be great. thanks. Phil

 

[WG M-B]

So a plug left in the engine that is said to be fine has blown the fused link in the relay? And probably the new relay? Is there 12v dc at the relay?

 

[Beese]

Heater Plug Warning Light

Hi - my Heater Plug light has started to stay on for approx. 30 seconds after moving off, all six were changed only 3000 miles ago - any ideas? Thanks

 

[whitenemesis]

It goes off, then comes back on for approx 30sec?

One or more glow plugs faulty or possibly the glow plug relay failing. STAR diagnosis will point you in the right direction.

 

[The Duke]

OK Guys. Thanks for your input. will double check glow plugs, as all seems to point to these. Thanks for you help. Phil.

 

[V6Matty]

i did have a problem with mine once where i had a faulty one changed it for a none branded one from a motor factor who said it will be fine, worked for about a week and failed again, they kindly replaced it FOC i fitted the new one and 2 weeks later it failed. took it back got a refund and bought one from Merc dealer havent had a problem since. have since replaced the rest of them just to be sure no more would fail and have to admit during the winter my car starts every time with only a couple of cranks of the engine before firing.

i think i read somewhere that the plugs can have a slightly different amp rating to Merc ones, so could be that this different ampage is causing the problem?

 

[Little Phil]

Silly question, when you say Glow plugs, do you mean spark plugs? are they 2 separate things?
My R320 showing similar symptoms... curly wurly dash light comes on, goes out when started then comes back on for 30/40 seconds then goes out.
Car starts normally and seems fine.. had this issue for 9 months or so with no apparent difference to cars characteristics

 

[mersum1es]

Silly question, when you say Glow plugs, do you mean spark plugs? are they 2 separate things?
My R320 showing similar symptoms... curly wurly dash light comes on, goes out when started then comes back on for 30/40 seconds then goes out.
Car starts normally and seems fine.. had this issue for 9 months or so with no apparent difference to cars characteristics

Spark plugs are in gassers (ignite air fuel mixture), glow plug in diesels (pre heats cylinder of the cold engine so that compression ignition happens easier). Your light behavior indicates faulty glow plug.

Edit: modern diesels are not requiring all glows working, though in colder conditions some starting issues may be detected if engine has lower compression ratio (like MB V-engines). Inline CDI engines are more robust.

 

[Frontstep]

A simple test of the glow plugs, which are essentially simple electrical elements should show up a faulty one.
They either work or they don't.
An ohmeter will tell all, it does not warrant a star test at this stage.