W221 320cdi glow plug light on after start

traffic0703

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My S320cdi (2006) has developed a glow plug issue.

The glow plug light has started to come on after engine start. On the first cold start of the day all normal.

On all 4 subsequent occasions today the light has initially gone out but come back on shortly after engine start but only stayed on about 10 seconds. After that has not come back on for the duration of each journey.

On all occasions the engine was not stone cold but at about 40-50 degrees so happening during the warm up phase only.

My Mercedes used warranty runs out in 2 weeks - if it is a glow plug I am not covered but if the relay is faulty I am insured.

What is the likely cause?
 

tode

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Quite likely to be a glow-plug, but could also be the relay.

Can be both (if the glow-plug has gone short-circuit).

If your warranty runs out soon, best to get it seen to ASAP.
 

Parkgate

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Its either a duff glow plug or the relay, don't worry about it, (probably just a gp) your CDI doesn't need fully functioning glow plugs in the UK. I changed all mine, the difference is....absolutely zero...except the light goes off and stays off....so book a nice hotel and have a weekend away for the same money, or burn a wad of cash.
 
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traffic0703

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On this engine, how long does it take to change a couple of glow plugs?
 

tode

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If all goes well, it's done in an hour. But if you snap one of the plugs, considerably longer (and more expensive).

In general, it's best to get problems sorted straight away.
 

M80

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With an ohm meter check the plugs, if any are shorted or open circuit then that's most likely the reason for the light. With plugs replaced you will then find out if you have to claim for the relay (£200 +)

If you're changing them you might as well do all. Beru seem to be a reasonable price these days and there are bad reports from the fitting of the alternative brands.

I would allow a bit longer than an hour but start pre treating a few days before change out. They might be ready to come out easily but a little WD40 into the recess and running up to temp for a few days might improve their readiness to come out.

Remove from a hot engine.
Get a torque wrench that can reliably torque at 7Nm, these plugs twist very easily.
 

ThinkPad

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Get it on star and you will have your answer. As said could be either. On one of my cars had to do the relay. On the other It was the plug. I changed all at same time which makes sense once you get someone in there.

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denchen

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I had the same light come up on my C200 about 3 weeks ago. I got a pair of long nosed pliers and gently pulled the caps off the heater plugs one at a time and with a multi tester checked the readings. 3 of the plugs were the same except number 3 plug was giving no reading at all. Off I goes to see my mate at Andrew Page auto factors who have various makes in but my mate says Bosch are better than Bero. I got just the one plug, about 10 quid, came home and whilst the engine was still hot got my sockets out, no oil or WD40 etc, and keeping the socket straight I gently put pressure on the plug. Out it came no problems. In went the new one and the light no longer comes on after initial cold start.
 
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traffic0703

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does Star store the fault

hi and thanks for the answers.

Car in tomorrow with the main dealer in case I have a valid warranty claim.

Out of interest, does Star store the fault each time the warning light activates?
 

dav1952

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My S320cdi (2006) has developed a glow plug issue.

The glow plug light has started to come on after engine start. On the first cold start of the day all normal.

On all 4 subsequent occasions today the light has initially gone out but come back on shortly after engine start but only stayed on about 10 seconds. After that has not come back on for the duration of each journey.

On all occasions the engine was not stone cold but at about 40-50 degrees so happening during the warm up phase only.

My Mercedes used warranty runs out in 2 weeks - if it is a glow plug I am not covered but if the relay is faulty I am insured.

What is the likely cause?
My w221 2007 has had the same issue twice both down to faulty glow plugs. If you take off the rectangular connector that fits into the glow plug controller @ the front of the car ( best to remove the controller first ) when you look into the connector there are 6 terminals on the left hand side 2 @ the bottom on the r/h side and 1 at the top r/h side.. working from the bottom of the l/h side of the plug working upwards the glow plugs are connected as follows.. 1st 3 terminals are.. l/h engine block front middle and back glow plugs respectively the 4th is r/h engine block front glow plug .The r/h side of the connector the 2 terminals on the bottom r/h side are r/h engine block middle and back glow plugs if you put a ohmmeter with 1 lead to earth then put other lead on the terminals above in turn should highlight any faulty glow plugs , when testing via the connector a good glow plug will show approx 2 ohms just compare the readings on each plug.Hope this helps..Dave
 

Mr Filipov

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Its either a duff glow plug or the relay, don't worry about it, (probably just a gp) your CDI doesn't need fully functioning glow plugs in the UK. I changed all mine, the difference is....absolutely zero...except the light goes off and stays off....so book a nice hotel and have a weekend away for the same money, or burn a wad of cash.

Not quite. The CDI does need the glow plugs. When I had a duff plug or two and the relay went as well, it was a bastard to start in the morning. It will start on the second turn of the key with a bunch of white smoke from the unburnt diesel. It was the same 320CDI iteration as the ops.
 

Steve@Avantgarde

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Star will store frequency counts if the same fault code is stored.

Glow plugs aren't just used for engine start (contrary to popular belief) they can even be used at 70mph with a hot engine. Which is why the glow plug relay is more like a control module. It measures the fuel temperature constantly and will use the glow plugs to give the optimum burn temperature.

Which is why CDI glow plugs burn out a lot more often than in a regular pump diesel engine.
 

Wighty

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Star will store frequency counts if the same fault code is stored.

Glow plugs aren't just used for engine start (contrary to popular belief) they can even be used at 70mph with a hot engine. Which is why the glow plug relay is more like a control module. It measures the fuel temperature constantly and will use the glow plugs to give the optimum burn temperature.

Which is why CDI glow plugs burn out a lot more often than in a regular pump diesel engine.
Thanks Steve , that's the first new thing I've learnt this year :D . ( only 3 left now !)
 


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