Cylinder 1 Glow Plug circuit question

[clanc]

Hi all,

I got a yellow engine light twice this week, and Obdelelven tells me that it's the glow plug circuit... error Code P067100.

I cleared the error and drove on both times...

A quick Google told me it is not too critical, but would appreciate your advice on the  urgency, and what will likely need doing, as I have the car abroad atm.

 

cheers 

 

[ApertureS]

Glowplugs are critical for a newer tdi. They assist with DPF regens and without them functioning the car will refuse to regen and instead block up the DPF.

[J.R.]

What function do they carry out?

 

I am not doubting you as I know you work with these vehicles but I have read everything that I could find on the subject (to keep up to date) including the VAG self study guides, I recall the measures to raise EGT above 600°c, EGR stopped, post combustion injection etc but not any glowplug intervention and I can't hypothesise how it would help.

 

Notwithstanding the above if a glowplug fault code prevents DPF regens the OP should indeed consider the fault an urgent one.

[ApertureS]

2 hours ago, J.R. said:

What function do they carry out?

 

I am not doubting you as I know you work with these vehicles but I have read everything that I could find on the subject (to keep up to date) including the VAG self study guides, I recall the measures to raise EGT above 600°c, EGR stopped, post combustion injection etc but not any glowplug intervention and I can't hypothesise how it would help.

 

Notwithstanding the above if a glowplug fault code prevents DPF regens the OP should indeed consider the fault an urgent one.

Take a read of Denso's little write up on glowplugs - Not 100% if the VAG group are included in this but i have no reason to think otherwise. Same way some glowplugs are not just a 12v feed but are a variety of voltages and even PWM now to more accurately control things. 

 

https://pmfmag.co.uk/features/denso-discusses-the-role-of-glow-plugs/

[J.R.]

Thanks.

 

Having read it I think the info contained within regarding glowplug actuation during DPF regeneration is just plain incorrect.

 

The engine has to be at operating temperature with the oil and water above a certain threshold as well as RPM etc, well beyond the minute or so after a cold start where glowplug actuation might be maintained.

 

The exhaust temp must indeed be above 600°c for active regeneration, post combustion fuel injection takes care of that as does stopping EGR, using glowplugs to preheat a mixture that is already being 100% combusted by the diesel cycle is not going to raise the temperature of the exhaust gases.

 

Were there to be an additional injector just upstream of the DPF for the post combustion injection (would make more sense and avoid oil dilution) then I could perhaps see the need for a glowplug also but with the EGT well above the flashpoint of diesel probably not.

 

Perhaps some manufacturers do use such a system, it's what I would do for a city car that would spend a lot of time at low revs and low power, such a system could regenerate at tickover.

 

I have never been comfortable with using the cylinder injectors for post combustion injection to increase the exhaust gas temperature.

Edited 18 September, 2022 by J.R.

[Hozz]

My daughter's 150 TDi had two glowplugs fail and I was concerned about regeneration even though a VAG dealer said it would be ok.

In fact she drove around for 3 months before getting them replaced, the regeneration worked fine and there were no ill effects.

 

[varooom]

I could be wrong, but my understanding is the glow plugs are for very cold starts (obviously) but they also function in the emissions whilst warming up iirc. to keep them under control.

 

I don't think I have ever heard of it being used as part of the DPF regeneration cycle.

[ApertureS]

4 minutes ago, varooom said:

I could be wrong, but my understanding is the glow plugs are for very cold starts (obviously) but they also function in the emissions whilst warming up iirc. to keep them under control.

 

I don't think I have ever heard of it being used as part of the DPF regeneration cycle.

It used to be a simple case of glowplugs for cold starts. Nowadays with fuel so clean, glowplugs arent needed for cold starts hardly (at least in the uk) im not saying they arent used, because they are as this reduces emissions on cold starts and allows the engine to warm up quicker and reduce knock.

 

That being said im not saying VW use it in their TDIs as im not sure, but many manufacturers do.

 

Quote from Denso above, quote for NGK below

 

Quote

3. Regenerating the DPF
Intermediate glow is equally vital to diesel particulate filter health. Although the DPF has a continual mission to reduce diesel car emissions, it only has limited capacity to capture and store exhaust soot. It therefore has to be regularly ‘regenerated’ (trapped carbon must be burned off) in order to continue filtering effectively. Wilschrei continues: “To regenerate, the DPF must be heated up to more than 600 ^oC for around ten minutes. The ECU therefore initiates a number of measures to achieve this, one of which is a so called “regeneration glow” from the plugs of well over 1,000 ^oC, even if the engine has warmed up. This raises the combustion chamber temperature, which in turn increases the exhaust gas temperature; supporting DPF regeneration. Defective glow plugs, however, can lead to the point that the DPF cannot be regenerated, causing clogging, which in turn means an expensive DPF replacement will be necessary.”

https://www.ngkntk.com/newsroom/blog/emea/glow-plugs-the-exhaust-system-heroes-and-why-a-summer-service-is-key/

 

Glowplugs arent a simple item either anymore.... theyre a whole lot more complicated with PWM glowplugs and cermamic tips.