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Hi the term Audi use is reducing agent, it is actually adblue and the term is derived from the system our cars use which is Selective Catalytic Reduction, the system works thus, you will have three sensors before the cat one is an exhaust gas temp sensor the other is an oxygen sensor the last one is a Nox sensor of which there are two, the correct designation are upstream for before cat and downstream post cat, before all of these is what is basically a small captive shower head which when commanded by the ECU will spray adblue into the exhaust stream pre the first bank of sensors, the first NOX sensor registers the amount of Nox in the stream and the second registers the particles after the adblue spray and depending on its in formation log may request more adblue, the whole mixture is then fed into the DPF which does its thing with the soot particle entrapment, here lies the problem to make the exhaust cleaner still there is an EGR cooler at the back of the DPF which is attached to another EGR valve which when opened by the ECU at low speeds sucks the already treated exhaust gas through the cooler with drastically cools the gas to so when it is reintroduced in to the engine to be re burnt by the combustion cycle it won't be to hot which reduces combustion temps and burns any Nox 1 that escaped the first time, as I said the main culprit for the blockages is the PCV system as this adds extra engine oil vapour and water vapour neither of which burn very efficiently if at all. thats why Audi recommend longer faster journeys as at higher speeds both EGR valves are shut as the engine needs as much oxygen rich air as it can get to maintain the speed therefore it burns slightly hotter and burns off a lot of the accumulation from town/city driving. Steve.

Superb explanation as always, thank you. The only diesel I use is Esso. And i'm using the Archoil now instead of the Millers. Oil is either Comma Prolife 5w30 or Castrol Edge 5w30 ll. I typically change oil (drain from sump plug) and filter every 6 months, which is usually around 8-10k miles. What are Audi referring to as "reducing agent" and if it's the AdBlue, how is that even getting back to the EGR cooler???

Hi your regeneration intervals are spot on, with regard to the adblue its not made of pigs urine which would require vast amounts of purification before use, its made of a component in the fertiliser industry which when mixed with de ionised water creates a synthetic ammonia, when subjected to extreme temperature the greater water element turns to steam and along with the ammonia turns the nitrogen oxide particles, Nox 1 into a inert particle Nox 2 which degrades rapidly in normal atmospheric conditions. Almost all the branded adblue sold in todays market are the same and unlike fuel do not suffer with blending differences, the consumption of adblue is very dependent on fuel/oil quality I.E. if you use supermarket fuel and cheap engine oil the regeneration factor will be increased as the amount of soot produced by both is accelerated and the DPF blocks more rapidly as the soot particles will be larger and physically more dense, therefore if you use good fuel and any Quantum spec low SAPS oil you are safe, with the additive going into the fuel as long as it has a Cetane booster that raises the burn quality this promotes much smaller soot particles which burn of more comprehensively from the core filters on the DPF. Steve.

Just an update on this, I knew my gut was right, only 3 out of 6 of my glow plugs were working! 😮🤦‍♂️ So I've had them changed for new bosh components. On top of that the battery was only working at 55% capacity! I also had the glow plug relay changed for peace of mind, but keeping the old one as a spare on the road trips. Needless to say my A6 is all ready for her adventure this weekend. More to follow in that once I'm back 😉

Mirrors aint cheap these days!

feeeeecccc me thats dear

Worth having a check Phil? Kind regards, Gareth.