Location of Glow Plug Control Unit on W124

[SilverSaloon]

Hi

my E300 Diesel saloon (1995 W124)'s glow plug light doesnt illuminate when you switch on the ignition (key pos II). car starts fine however and then the light comes on and it glows until you drive the car away.

i have read that this could be either down to knackered glow plugs or the fuse in the glow plug control unit, so thats my 1st point of call.

anyone know where its located or know can actually diagnose my problem?

how hard are GP's to change?

thanks

Derek

 

[Dieselman]

The glowplug relay unit is mounted on the inner wing in the engine bay.

Follow the leads back to a box about 3" x 2" x 1.5".

To change the plugs is easy once the intake manifold is off.

If it starts ok then there's nothing likely to be wrong with the plugs but they can be metered from the glow relay connector as they are individually fed.

 

[TonyVianoAmbiente]

My E300 Diesel saloon (1995 W124)'s glow plug light doesnt illuminate when you switch on the ignition (key pos II). car starts fine however and then the light comes on and it glows until you drive the car away.

i have read that this could be either down to knackered glow plugs or the fuse in the glow plug control unit, so thats my 1st point of call.

Hi Derek,

I hope your caravan holiday went well.

I have exactly the same problem with my E300 Diesel. My car's glow plug light behaved perfectly pre-veg oil. Could it perhaps be a veg oil issue?

Tony

 

[SilverSaloon]

will a 1995 W124 definatly have a fuse in this box? there is a box i've found (only one i can see on the passenger side) but it only has 2 block connectors in it - no fuse....

 

[SilverSaloon]

Hi Derek,

I hope your caravan holiday went well.

I have exactly the same problem with my E300 Diesel. My car's glow plug light behaved perfectly pre-veg oil. Could it perhaps be a veg oil issue?

Tony

hi tony,

i suspect it isnt a veg issue as the saloon has only done about 1000 miles on about 70% veg - whereas the estate thats done almost 8000 miles on veg has no glow plug issues (oh no i've gone and said it now!!)

 

[230K]

Hi

Your glow plug relay is beside your abs pump and self levelling reservoir about the sixe of a BIG match box. Pull off the cover and detach the plug with 6 wires going into it. On the underside of the plug it is numbered 1-6. If you test the resistance from each of the connections to earth any bad plugs will show up.

230K

 

[SilverSaloon]

is there a fuse for this?

 

[KLP 92]

i don't think there's a fuse.

Had the same problem on a w123 diesel, i believe my dad changed something (a resistor?) in that control unit.

It happened on another w123 diesel, same prob but started working again by itself after a few weeks.

 

[SilverSaloon]

i don't think there's a fuse.

Had the same problem on a w123 diesel, i believe my dad changed something (a resistor?) in that control unit.

It happened on another w123 diesel, same prob but started working again by itself after a few weeks.

i may swap the unit with the one from the estate and see if it fixes the issue - if it does i guess i can source a 2nd hand unit

cheers

 

[KLP 92]

i may swap the unit with the one from the estate and see if it fixes the issue - if it does i guess i can source a 2nd hand unit

cheers

If its the unit, its not necessary to replace if the car starts ok.

All that happens is that the light won't light up when you start, if you listen carefully you'll hear the "click" which indicates its ready to start. Or just wait a few secs from starting to give the glowplugs time to heat up.

 

[TonyVianoAmbiente]

If its the unit, its not necessary to replace if the car starts ok.

All that happens is that the light won't light up when you start, if you listen carefully you'll hear the "click" which indicates its ready to start. Or just wait a few secs from starting to give the glowplugs time to heat up.

That's good advice.

Despite the strange behaviour of my car's glow plug light, I know the glow plugs are working. If I try to start the cold engine straight away, it won't fire. If I put on my seatbelt and turn on the radio, at which point the light used to go out, the car starts as normal.

 

[Number_Cruncher]

It's possible that there's a wiring fault.

The glow plug control unit relies upon the signal from the temperature sensor located under the inlet manifold (quelle surprise!) towards the rear of the cylinder head.

I found the insulation was badly degraded on my 1995 E300D, and I could easily imagine a short circuit there could confuse the glow plug controller.

 

[SilverSaloon]

thanks for everyones input. i've got to have a proper look at this over the next few days but the weather has been poor and my garage is full of stuff to get the car in at the moment

but i did find this link that i hope will be useful so here it is for others:

http://www.dieselgiant.com/glowplugrepair.htm