Essentially if the DEF fluid pump is supplying less than prescribed fluid quantity either by flow/pressure discharge into the mixing chamber where the injector is sited due to a fault, the temp sensor (a thermo couple) just down stream will record an over temp fault. It will throw a code!
Of course one of the reasons for pumping 95% of that pure water in DEF fluid is to cool it (exhaust gas) down so that NOX is reduced by chemical/molecular association to base elements
Remember 4/5th of the atmosphere is N2 and if you heat it as part of regen-(de soot) above 2800 dgf dis-association of the elements occurs and you get Nox. Brown smog ozone etc. However "Prompt Nox" starts occurring at about 450dgf and increase with temperature rises especially during de soot
The next thermo couple to see further down the exhaust body is also measuring the temp at the end of the exhaust cycle. The PCM by comparing the temperatures, is able to correlate the inputs of live date and determine if cleaning and toxic gas purification is taking place.
So if the DEF fluid is not being pumped out you may get a code for flow or pressure and with it often comes an exhaust gas over temp.
I had one last week with a clogged up injector, in fact I could feel the "crunchiness" of crystals in the pipe feeding the injector. I cleared it by removing the injector assy and commanding fluid discharge by scanner bi-directional interface and watching it pee out after clearing.