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Glow plugs pre-heating when they shouldn't?
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wasted   
Mon Feb 17 2014, 10:14pm
Joined: Feb 12 2012
Member No: #799
Location: Cambridge
 I've noticed that my glowplug preheat light comes on most mornings at the moment. Its seems a bit strange because winter is so mild this year. From what I've read on here it should only need pre-heat if it's properly cold.

I'm guessing dodgy coolant temp sensor but nothing comes up if I read the codes via a generic ODB2 scanner. Is it worth swapping out for a new coolant sensor? I cant think of any other way that it would know the ambient temperature?

Cheers.
Dave Mc   
Mon Feb 17 2014, 10:35pm
Joined: Mar 02 2010
Member No: #64
Location: Weston-super-Mare
 I've got the C5 with the same 2.7 engine and my glow plug preheat light has been coming on. Not something I would worry about, as it's been so windy it has resulted in the engine block becoming very cold.
Tjensen   
Mon Feb 17 2014, 11:51pm
Joined: Jul 17 2012
Member No: #954
Location: Bergen
 Glow plugs start to function a bit below 10 celcius and way before 5 celsius, I think.
gmerry   
Tue Feb 18 2014, 02:02pm
Joined: Dec 11 2009
Member No: #21
Location: Scotland
 Without wishing to over-complicate this, I'm guessing that the glow plug warning lamp is NOT directly related to the status of the glow plug function.

In other words, the glow plugs may come on in normal cold start service without the driver being aware. The warning lamp is just there to say "wait a minute for the glow plug to heat up because the block is VERY cold". Normally there is no need to wait and so no lamp appears.

If the lamp is always coming on, even for mild weather starts, this would indeed point towards a system component having failed or being faulty.

Note, over 4 years of Scottish winters, I have probably only had the warning light come on maybe 5-6 times.

Regards

G
magicands   
Tue Feb 18 2014, 02:18pm
Joined: Sep 13 2012
Member No: #1021
Location: Coventry, Warwickshire
 My pre heater light has been coming on most mornings just lately, its not a fault but just down to weather and atmospheric conditions, I'd forget about it as its not a fault.
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wasted   
Tue Feb 18 2014, 07:28pm
Joined: Feb 12 2012
Member No: #799
Location: Cambridge
 OK. Thanks all. I might replace the coolant temp sensor next time I service and see if it changes anything but I wont loose any sleep over it if its a common thing
ChrisHunter   
Wed Feb 19 2014, 09:51am
Joined: Jul 20 2010
Member No: #188
Location: Lancashire
 as we understand it, HDi engines use the glow-plugs (suitably controlled) to help all-through engine warm-up, all year ... presumably the light is informational, because delays could be handled automatically ... ours is garaged overnight & have never noticed it !
 

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