Originally Posted by T-Stick
I was not asking if it had a DPF (Diesel Particulate Filter) but whether it uses the DEF fluid (Diesel Exhaust Fluid) and uses regeneration cycles like a larger diesel. So while they are similar in that they both regenerate the use of DEF with the DPF was part of the problem they were having. The DEF was gelling in the cold temps and causing regen problems. I understand you use DEF also--I was not aware that SCR means that. Most experienced diesel mechanics will tell you that the tier 4 diesels are much more prone to failure--whether in farm equipment, OTR trucks, or small diesels. That is simply the statistics of the industry--not to mention how detrimental tier 4 is to engine longevity. Adding cold weather to the equation only increases the chance of failure. Your good experience with a BMW does not discount the fact that tier 4 diesel systems are far more prone to failure.
However I don't doubt that BMW likely has a superior execution of a Tier 4 system than what is in the GMC Canyon and I don't doubt the reliability of your reporting. Day after day of driving in those temps will find any weakness in a tier 4 system, while an older diesel without those systems will just chug right along with the proper fuel.
SCR-Selective Catalytic Reduction. Anything after 2009 in the US in passenger diesels has to have SCR to be compliant with EPA and CARB requirements.
However, you are right, SCR system, especially first generation that I had on BMW are prone to failures. BMW was actually very reliable except SCR system (take that out I only had to deal with open thermostat).
While BMW did not have these "rookie" mistakes, system itself is overly complicated for every day use, on top of that due to BMW chasing weight distribution, it had two tanks which added to complexity since DEF had to be transferred from passive (larger non-heated to smaller, heated tank). Keeping this part in best shape required some interest in system, as solution was to always fill passive tank, never active tank and with that keep system constantly working. That added additional plumbing on top of already complicated plumbing. The heat unit in active tank was prone to failure which BMW only replaced as tank assembly ($2,400. Luckily mine failed during warranty period). However, heat unite could be purchased for VW Touareg and Audi Q7 TDI and some other vehicles as it is same, and it was like $206 and some 3hrs of work. Passive tank had level sensor issue, but nothing that $5 resistor could not resolve it. The biggest problem was diagnosis once SCR sensors go bad. Is it pre CAT or post-CAT sensor? Is it DEF injector or SCR mixer (CAT). The second generation BMW utilized on X5 F15 and 328d F30 was much more robust, but with all these moving parts it is really not worth it.
However, all this would not leave you on the road. Active, heated tank was in engine compartment very close to exhaust manifold.
On other hand I had BMW E61 525d in Europe that just had DPF, not SCR, and made 485k km, was starting as low as -42c, and never had any failure except two thermostats and one EGR.