Gary s said:
I am aware the design of the exhaust is supposed to be not ideal leading to issues so I am going into this with an open mind but to date car is great and is driven slightly on the harder side which may be helping but only time will tell I suppose
I believe the highlighted phrase explains why some cars do better than others in this regard. We know from JLR's candid disclosure that during "normal" driving the DOC is ineffective and all the soot has to be collected in the SCRF(DPF) box. This leads to a requirement for
more frequent active regeneration events and then, due to the architecture, each regeneration lasts
longer which increases the risk of an interruption. The price to be paid for an incomplete regeneration is additional DPF warm up time the next time the engine is started. "More frequent" and "longer" periods of post injection are referred to in the SCN and that, I think, completes the narrative of why it occurs. How it affects ownership of the car depends on driving style - and there are broadly three styles to consider:
1. Driving "hard" reduces the frequency of regeneration events because it lights up the DOC to some extent and therefore less HC/PM arrives to be collected in the SCRF(DPF). Based on an analysis of forum contributions, a pre-N289 car driven in this fashion will reach 12,000+ miles before the diesel dilution reaches the safe level of 6%. For these drivers, an increase to 20,000 miles can be expected before the service message appears once N289 has been loaded.
2. The problem is amplified by calmer driving styles and respect for national speed limits. For this type of driving it doesn't make any difference whether journeys are 45 minutes long or 4 hours long because driving sensibly/economically (what JLR referred to as "normal" or "typical" driving) never lights up the DOC. Ever. With this driving style owners can expect 6,000 to 8,000 miles between pre-N289 oil changes, 10,000 to 14,000 miles after the update.
3. The problem becomes super-critical when journeys are regularly sub-45 minutes. Now the owner will be lucky to make 4,000-5,000 miles between oil changes. But that's not the worst problem - because now the DPF will start to regularly clog with soot and amber/red DPF lights will appear. It will have to be "coaxed" into regenerating. But eventually most of these cars will need a new DPF and so for them N289 assumes all the utility of a chocolate tea-pot.
So how many diesels in each category? Sticking a finger in the air having looked through our various surveys I would say the distribution has a "classic" normal distribution curve - about 10-80-10.
It's clear that 80-90% of drivers have the wrong driving style, just as JLR have been saying.
But is that the driver's fault? Or the manufacturer's ...?