intermittent glow plug light

[Whizzkid]

Hi. All.

 

Its that time of year, my TDI 2.0 Mk2 2011 glow plug light initially does not come on, so obviously with temps as they are the car will not start. After 2 or 3 tries the glow plug light comes on, goes out as normal and car starts. I am fairly certain its not a glow plug as the would normally show as the glow plug light staying on or flashing, in my experience. I am thinking relay is getting a bit tired. Not sure if that's possible or do they either work or not ? Battery good and fully charged, no codes coming up.

Any thoughts gratefully received as always.

[J.R.]

When you say "obviously" are you saying that the car does not start or you believe that it would not start without the glowplugs doing their job?

 

I ask because my MK2 Octavia would always start on 1/4 turn with or without glowplugs no matter how low the temperature got, they were all open circuit and replacing them made no difference.

 

My Yeti has the same engine as yours and its currently hovering around zero degrees, it still starts immediately and I will continue starting it without waiting for the glowplugs until the temperature drops low enough for it to not immediately start & run on all 4 cylinders if it indeed happens.

 

I am actually doing this to preserve the battery, the voltage drops considerably after the glowplugs have heated, if as at present it will start instantly and run without misfire I dont want to make the starter labour and finish off the battery which is past its prime.

[Whizzkid]

Interesting. Not my experience of glow plugs and diesel engine. The temp sensor will normally activate them below about 5C . Anyone have any thoughts on original question re the relay please.

[keef690]

Hi. I see you got little help with this! Did you find out the problem? Relay, control unit, fuse maybe. Mine is doing the same, if the glowplug light lights up for a while it starts fine, but if there is no glow plug light, then it will not start. Thanks for anything you can tell me.

[Whizzkid]

Unfortunately not. I did change the GlowPlug relay as a formality really. Is it still works fine for a couple of weeks even though it is being used every day and then one morning just does it. Couple of turns of the key on and off or leave it for 10 mins and then glow plug lights on and fires up. Once it has started in the morning it has never done it again during that day. Its obviously an electrical contact somewhere. No fault codes show which is the frustrating bit. I know we are not alone, Passats with the 2l diesel suffer from it as well. My feel is that is might be the electric lift pump which should fire up as you unlock the car. All the normal suspects such as coolant sensor, ignition switch, keys are fine. I really don't feel like keep replacing items on the hope that I might get it right one day. If anyone else has cured this issue it would be good to hear from them.

[keef690]

Thanks for coming back. I will try the fuse, then the relay and then the control unit. If I ever solve it, I will post here for you. Cheers

[Whizzkid]

Thanks , same here . Best of luck.

[Breezy_Pete]

Relay is the same thing as the control unit. It's all solid state now, no moving parts.

[pastiche]

Since I charged my battery the light goes off when starting. I was not aware the battery might be down as it always start right away.

[keef690]

On 23/02/2021 at 09:11, Wino said:

Relay is the same thing as the control unit. It's all solid state now, no moving parts.

Actually this is incorrect I believe. The relay is the big square one in with the fuses under the bonnet. Mine is marked 100. The control unit is under the fuses and you slide it out after removing the battery for access. Two very different items with different part numbers. I have noticed a lot of people on here think the relay is the one underneath the fuses. Pics attached for anyone's reference. 

[Breezy_Pete]

What car do you have @keef690? Year and engine code.

What makes you think that relay has anything to do with the glowplugs, or are you not claiming that?

The OP's post certainly seemed to be referring to a 'relay' in relation to glowplug function, in my opinion? That was what I was talking about.

 

[keef690]

2011 Octavia Scout. As I understand it the relay works with the control unit and either could be the cause of the intermittent starting. Of course it could be the sensor, ecu, ignition etc etc. I am just starting with the easiest ones, as nobody on here or any VW forum seems to have cured it yet.

[Breezy_Pete]

Engine code or I can't help.

 

[keef690]

CFH

[Breezy_Pete]

OK, well your glowplug control unit does have one direct dependency on that relay. The output of that 100 relay feeds into the glowplug control unit via fuse 15, as a non-permanent 12V feed. (It feeds many other things too).

The glowplug controller has 9 connections; four to the plugs, one permanent 12V, one earth, two to the engine ECU and this one from fuse 15.  

 

That same fuse also supplies the coils of the fuel pump relay(s) on your engine so seems like a good one to check in case of non-start.

 

 

Edited 24 February, 2021 by Wino

[keef690]

Thanks. Will post if I get anywhere with it.

[keef690]

Just thought I would post that changing the relay worked for me. Has started every time for 2 months now. The relay in question is the big square one in with the fuses under the bonnet, marked 100 on mine. Not to be confused with the control unit under the battery, I did not change that. Hope this helps someone and maybe Whizzkid you can edit the title to say solved?

[Whizzkid]

Will try that one keef690, I have had no issues with mine since the weather improved ( no its not the coolant sensor ). The biggest factor in my mind was I gave it a good pasting on a 3 hour motorway journey so everything got really nice an hot. It has spent a lot of time sitting on the drive and only doing the supermarket run, during lockdown. It has never done it since. I will get a 100 relay and sit on it . If it does do it again will change that next.