Not sure whether this is the correct place for this, but as I didn't find any other specific place I'll just put it here (since the 3.0 TDi is common to a nr of Audi models) and if it has a more correct home to be sent to, I'd be grateful if the mods could redirect it there ...

OK, 2011 manufactured A6 allroad with std 3.0 TDi. Car was previously owned by a inner city dweller that only used it for short trips and managed to only put 80 000km on in 9 years, so lots of short journeys. I bought it in early 2020 and had it gone over and serviced by Audcare who looked after my previous A6 quattro Avant (unfortunately a victim of the great Takata 2019 airbag recall) post Strecker, post Audi Sydney.

The allroad did a lot of back and forth 300km journeys in the first two thirds of 2020, but in the latter 4 months, it's mostly been on 20km 80km/hr ones daily. The glow plug light and engine light started to come on randomly and occasionally would go into limp mode in December. Had it reset but would again randomly occur. It has always been fueled with Caltex Vortex diesel whilst in my ownership (about 15 000km) and 90% from the same garage on the far south coast.

In late January, I added Nulon Diesel Guard to a full tank of fuel and within a couple of days, the random warning lights disappeared (and have remained off for a couple of weeks now and no limp mode).

Is this a common way to resolve/prevent the dreaded EGR/DPF/other emission control stuff happening? Or will it eventually need to go the new part route? TIA, cheers.