Glow Plug Problem

[duncanh]

My glow plug light came on this morning as usual, went off after a few seconds, but came back on after the engine started.

As I drove away, I expected it to go out a few minutes later. It stayed on until I stopped about 40 minutes later.

I restarted the car, the same happened again. I switched off and restarted again, this time it went out and stayed out.

I have always understood that a faulty plug will cause the light to stay on for up to five minutes, but it will then go out.

If this is the case, I may have an electrical problem. Glow plug relay? Where is the control unit for the glow plugs on a 2002 W203 c220 cdi?

I welcome your thoughts, Faulty glow plug or faulty electrics? I will dig out the multimeter if it happens again.

What is the expected life of a glow plug (mine have done 186,000 miles in 7 years and are original. No problems until today). Also, as the battery is original, could this be an early warning? I am aware that odd things happen when the battery gets old and worn, although I have had no other symptoms.

 

[roadhog]

7 years for a battery is good going but it'll be past it's best. 186k is not a problem for plugs, I'm on 206k miles and still have some of the originals fitted. A lot depends on the type of use the car gets, lots of short journey or cold starts will shorten their life.
As for the rest, get the fault codes checked, that should tell you more.

 

[duncanh]

Same again today, the glow plug light stays on until I switch off and restart. However, when I tried a switch off and restart after 10 miles, it stayed on. Tried again after 20 miles, it went off.

Does this sound like a glow plug problem or an electrical problem?

 

[wireman]

Its unlikely to be the battery.

It is an electrical fault, the glow plugs are electric and have a cold resistance of about 1 ohm.

The lamp staying on is usualy an indication of one or more plugs gone tired, the intermittent nature of your fault may be the relay/control unit, one plug very much on its last legs or a poor connection.

Check each plug for continuity or if you can measure low resistances measure them and the resistance of their wires from the relay, expect 1 ohm (ish) or less.
Examine all the wiring associated with the power to each plug from the relay and the power and ground/body/earth to the relay. Pay particular attention to any crimp lugs, these can get some corrosion inside the crimp and go high resistance.
If the relay is powered from a terminal box near the battery as on 124 models check this as well.

Beware of the risk of breaking the plugs off whilst attempting to remove them.

 

[dizzy lizzy]

I have known glow plugs to last 250000mls but Mercedes recommend changing them at 70000. Hope this helps

 

[The Rock]

My 210 behaved similarly. I had all six plugs changed (my indy won't do just 1 - says it's not cost effective). Behaved correctly ever since.

Rock

 

[terry steward]

My wifes 06 c320 began to have problems last week,our warranty ended nearly 3 weeks ago,and now the glow plug light stays on,and we have to switch the engine on and off a number of times,before it will permanently extinguish,so we can carry on our journey.the car has done around 60,000 miles now

 

[Alex Crow]

oh, thanks for telling us.

 

[duncanh]

Problem solved!

Thanks for all the advice and help.

It was glowplug number 4, the one nearest the bulkhead. I took the top off of the glowplug relay and used a multimeter to test the resistance from the glowplug connector to earth. Plugs 1 - 3 were all just under 1 Ohm, plug 4 had no continuity.

I swapped it and the problem has gone away. It was quite difficult to get access to it as there were some electrical cables and a fuel line in the way. It is just possible to push them out of the way to get the glowplug out (and back in again).

The other three look easier to access, so I will leave them until they fail. I have had the car since new, so I know they have not been changed before. The original plug that I removed was a Bosch (with Mercedes logo). I thought MB used Beru.

Once again, thanks for the good advice.