Aftermarket June 2022

JUNE 2022 AFTERMARKET 29 With performance not affected, David was keen to establish if the urea consumption was excessive. This was confirmed as one tank urea per two of fuel. We know the injector is delivering the correct volume, so there must be another reason. Returning to the efficiency data, and injector delivery ratio he noted the following. Please refer to Fig,5 and Fig.6, which show SCR CAT efficiency. The NOx catalyst efficiency was well down at .354/.495 when 1.000 is correct, so the focus shifted to the catalyst efficiency. The vehicle has only done around 54,000 miles so we were not expecting a problem. Removing the exhaust system from the front and rear allowed inspection with our ender scope. So here is the rub; Look at the pre-repair and post-repair Datazap images as seen in Fig.7and Fig.8 Fig.7 shows yellow trace, SCR injector activity, excessive during normal smooth driving. Fig.8 white trace, NOx sensor 1 G295 upstream, high concentration NOx, 580ppm. Fig.8 blue trace, NOx sensor two, G687 downstream even higher concentration of NOx, 707ppm. Back to the specific DTC David extracted at the beginning of the exercise; NOx sensor G295 signal low? It is not low – it is just lower than sensor 2 G687, which is very high. The problem is now obviously a dead NOx catalyst. Further close examination of ECTA shows several update catalysts for this vehicle application, so the manufacturers have previous experience of premature failure. What? No recall programme? Don’t be silly. The active coatings which As technicians, we must be conversant with the systems we intend to interrogate ” reduce NOx, platinum, palladium, and especially, barium have obviously been insufficient in earlier substrate manufacture. Why are NOx higher coming out of the catalyst? Quite simple really; The rear sensor is reporting the incoming NOx plus the stored NOx in the dead catalyst. New catalyst Now let us look at the new catalyst. Please refer to Fig.9 and Fig.10. Fig.9, SCR injector activity normal, occasional intervention. Fig.,10 white trace NOx sensor 1 G295 normal NOx activity. Fig.10, blue trace NOx sensor 2 G687, passive activity confirming no NOx emissions. Straightforward? It can be, providing you follow the correct process with the correct information and tools, not forgoing the £2,000 for the catalyst plus our costs. This is why I love cycling! Fig 8 Fig 9 Fig 10 Fig 7 Fig 6 Fig 5 Fig 2 Fig 3 Fig 4