Update: The exhaust system on the diesel is quite complicated. The first thing the exhaust gas enters is the DPF, Diesel Particulate Filter canister. This one unit consists of two separate processes. First Oxidation Catalyst section and Diesel Particulate Filter, both in one assembly. This one container has three temperature sensors. First is at the input flange to the device, second is in the device, the third is on the output of the device. I was not able to find out which one of the three may be the problem. I have reasoned the first sensor experiences the harshest conditions so I have replaced that one, the first temperature sensor of this system. I hope this was the right choice. It's been four weeks now, five full fill ups of fuel, and so far so good. I like to think this problem has been resolved. To truly understand what is actually happening in this exhausting process one needs a degree in chemical engineering.