Anthony Nonymous wrote:
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


No specific advice Im afraid but if it hasnt 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 theyre 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
--
Please don't feed the trolls