VW Golf Mk6 (2011) 2.0 diesel: particulate filter & dash warning lights

[Anthony Nonymous]

Hello All. Advice appreciated and I would have posted also to uk.rec.cars.vw.watercooled, but that group seems to be pretty dead, now.

The problem: diesel particulate filter (DPF) light came on, briefly, about 2 weeks back. After a week or so of no problems, DPF, engine management and curly symbol light (glow plug indicator, but also indicating other issues) lights all came on and stayed on, with the car stuck in limp mode. Various amateurs plugged in assorted gizmos and failed to identify a relevant fault code. Handed over to a trusted local garage (independent) and their diagnostics also said all was well, so they reset the fault codes and attempted a forced DPF regeneration; no dice. Concluded that the fault might be any number of sensors, but that the investigative work would probably cost a significant portion of the car's value. So, we're stuck with car in limp mode.

One possibility for a faulty sensor (and by far the easiest to replace) is the pressure sensor for the DPF. The only issue is, a new one needs to be "adapted" to the car, by instruction from a gizmo. I'm not sure whether any of the cheapo gizmos (e.g. Carista dongle and app) will do the job and I'm not fancying paying for the VCDS software that VW use. On the off-chance that anyone knows, advice would be greatly received.

Apparently (according one of the amateurs and the garage), the DPF sensor is giving sensible values for the differential pressure either side of the DPF (what it measures to determine DPF clogging), so replacing that sensor is perhaps clutching at straws. Then again, no sensors were showing as faulty in the diagnostic tests run to date, so DPF sensor seems as good a place as any to start.

A question now more for academic interest than anything: how does the car estimate separate figures for soot and ash within the DPF if only differential pressure is recorded? Are other sensors involved? I've not come across discussion of them in documents returned in Google searches. It is perhaps of relevance that the soot figures on the limping golf showed a (clearly incorrect) large minus value on a "Carly" OBD2 data reader. If the combined feed of data from the DPF differential pressure sensor and A.N.Other sensor are processed to calculate the soot value, then presumably, we have to suspect A.N.Other sensor?

Thanks for any help.

Ant

[jon]

Just off the top of my head, I would change the filter first and if necessary disable the sensor.

[Tim+]

No specific advice I?m afraid but if it hasn?t been done already, they would be no harm in disconnecting the battery for a while (an hour maybe to be sure?) to see if that clears things and brings it out of limp home mode.

I would then check out the glow plugs as they are very much an integral part of emission control these days and if they?re not working properly, they could be responsible for your DPF issues. If you can get a multimeter on to them (access being the issue) it should be possible to see if any of them are open circuit.

It would also be worth checking out the VW forums for advice and maybe get a recommendation for a VAG specialist garage local to you.

Tim

[Tim+]

I think you?ll find changing the filter is non-trivial and costly.

Tim

[David]

Depending where you are, you could search the VW fora to see if there is anyone near you with a copy of VCDS.

People are usually happy to share once they have coughed up for the kit.

However we live in difficult times so mixing with strangers may be off the menu at the moment.

Cheers

Dave R

[Lee]

<snip>

Although the sensors are a known problem on these, depending on mileage and usage, the EGR or DPF could simply be clogged. Not what you want to hear, but not uncommon.

Firend (who is an independent mechanic) has had to to replace the DPF and EGR on 2 relatively low mileage Golf Mk6 in the last year. Not a trivial task either.

Apart from routine servicing, a large proportion of his workload is emmisions related problems with modern diesels. :( :(

[Fredxx]

All I can suggest is get an OBD reader and provide the fault codes. If the ECU has gone into limp mode I don't believe there aren't any fault codes.

[Tim+]

I?ve been thinking about this.

Ash isn?t removed by regeneration (as it?s non-combustible). I would guess that the system looks at the pressure across the DPF before and after regeneration. Any residual back-pressure after a regeneration cycle will be assumed to be ash. The reduction in back-pressure after regeneration will be soot.

Tim