Glow plug lamp stays on

[Danny DeVito]

Todays problem...my glow plug lamp was coming on after start for approx 2 mins then going out for a few weeks. Now it comes on after start and stays on all the time. Does anyone know why it changed? does it mean more plugs gone or a fault in the relay perhaps ?

 

[BlackC55]

Normally one or more glowplugs will be faulty

 

[Danny DeVito]

i think i wrote that a little unclear. initially the glow plug lamp only lit for a few seconds (normal conditions) Then for about three weeks the lamp would stay on for about 2mins after starting the car. Then a few days ago the lamp comes and stays on as long as the car is running. First i thought fine a plug is faulty but now why does it stay on all the time ?

 

[ianjay]

I had the exact same problem, and 3 weeks ago changed all the glow plugs.
All this did was sort it for 2 days, then it started again.
Last Thursday it went to Merc and on to the magic machine,
this showed up a faulty sender unit, and it was changed.
£85 later, problem solved.

 

[Danny DeVito]

I removed the sender unit and yes one of the circuits is burnt out. I have repaired it but its too late to test, i may do a 'How To' on the repair its quite simple. I just hope one of the gps is not shorted to earth

 

[ianjay]

Great, that's good news, at least you were able to do a repair.
A 'How To' for this would be very handy as it's apparently, a
common problem.
You would think the boffins at Merc would design a stronger
unit, but is that being silly, they would not make as much in
the parts department!

 

[paul m]

tv ianjay

Hi ian did u get sorted with analogue to digital tv as i am trying to do the same thing on same car?

 

[Uncle Fester]

Todays problem...my glow plug lamp was coming on after start for approx 2 mins then going out for a few weeks. Now it comes on after start and stays on all the time. Does anyone know why it changed? does it mean more plugs gone or a fault in the relay perhaps ?

It does say in the manual somewhere that the glowplugs and light will remain on for a short period of time after starting (2 mins seems feasable) if the enginine management system requires it for better combustion, and mine does do this from time to time, so I don't worry about it.
As yet I has not stayed on permenantly, but I'm sure it will at some time in the future as things wear out.

You say you found and repaired a fault in the sender unit, so I agree with the other guys that a how to would be most useful.

 

[panason1c]

The g/plugs do stay energised for a couple of minutes after the engine has started, to reduce black smoke, but the g/plug warning light should normally stay OFF during this period.

If all g/plugs are good and the light comes on for a short while after starting, or where the light stays on all the time, the usual reason is because one of the fusible links inside the relay has blown, which is the result of one of the g/plugs failing and where instead of the plug going 'open circuit' on failing, it goes into a 'dead short' mode, thus blowing the fusible link(s) inside the relay.

The relay repair is dead easy........just open it up and you will see a row of fusible links, just solder a 30amp fuse (with tags) over the blown link.

A cost of only pennies to repair instead of circa £85 for a new relay.

 

[Danny DeVito]

Quite right mR P1c. It seems that on my car that with previous owners the light came on,. then they got the plugs replaced but never repaired or replaced the relay. Then someone dismantled the dash and put tape over the warning lamp. So when i removed the tape i saw the lamp stay on for a while and i repaired the relay. It lasted a while but then blew the link, i suspect due to shorted plug /s . Sorry i never did the how to i have pics ready but never got to it (yet ) It's easy and clear to see when you open the relay though and plenty of room for soldering.

 

[merlin0251]

Hi newbi here , do you or any other know the location of the relay on the C270 cdi 53 plate. Thanks in advance

Grahame

 

[BlackC55]

Under the bonnet on the right as you look at it. A box with a big connector on it. The largest plug has 5 pins. One for every glow plug.