There has been some good info posted here and some not so good. I own a Ford 6.7 diesel with DEF injection and am also quite familiar with the GM as well. I hope all take what I am about to say as helpful information and not an attempt to belittle any brand. There is a lot to cover so this may be a long post.
DEF injection as emissions control has been around for several years, mainly in Europe. It is a mature system. Pilot Truck Centers have DEF bulk dispensers at many locations. The DEF runs $2.79 a gallon. Here is a link to the current Pilot locations that dispense bulk DEF.
Pilot Flying J - Locations with Diesel Exhaust Fluid
The product, as noted earlier is available at all major auto parts stores.
DEF freezes at 12 degrees F. The systems in both trucks are designed to accommodate freezing DEF. EPA regulations allow full operation of the engine at any time the DEF would be frozen. DEF is only injected into the exhaust stream at elevated Exhaust Gas Temperatures(EGT's). The higher the EGT's, the more demand placed on the DEF system. At cold operation temperatures, DEF is never injected. MY truck uses about 1 gallon of DEF per 1200 miles of driving during the summer. 8000 miles of towing my 13000 pound 3055RL have given me a good feel for the DEF consumption rate. The 1000 miles per gallon is inline with posted information as the GM does consume DEF at a higher rate. During these cold months my DEF consumption has dropped by 40%. This is also in line with predicted consumption at cold temperatures. I have had no problems with my truck.
The complaints about cold weather issues with some trucks are valid. The quantity of affected Ford trucks is very small and almost all of them are located in Northern Canada. There have been a couple in Alaska and 1 reported truck in the Vermont area. All events so far are in ambient temperatures well below 0 F. Ford's problem has been identified as a DEF/NOX sensor calibration problem. Some trucks have a NOX sensor that has an out of specification range and a wider reporting ability than the interpretation software allows. When this happens, it looks to the software like there is a problem and a Check Engine Light(CEL) appears. Ford investigations have shown that 95% of these CEL's are nuisance reports. Dealers are instructed to check for DTC codes and turn off the CEL light. If the CEL light reoccurs, the customer is told to drive the vehicle normally and ignore the CEL for the time being. There is nothing inherently wrong. The Ford does not go into limp mode with this problem. Ford has developed the software solution for recalibrating the DEF NOX sensor parameter problem. However, because this is an emissions problem, all software solutions must be approved by the EPA. As soon as the approval is granted, the necessary programming changes can be made.
Unfortunately, as of last week, GM's problems are more in number, cover a larger geographic area and a wider and warmer temperature spread. The ugly side of their problem is a large number of the affected trucks go into limp mode. There have been a couple of temporary software updates issued to stem the spread of the problem. I do not know what the success rate is for the latest revision. These upgrades must remain temporary until the EPA approves whatever final software update that GM proposes.
What is really ugly about this whole mess, for both manufacturers, is that all trucks coming off the assembly lines are required to be programmed with the current approved emissions coding. This means that even if the solution has been developed, they can not apply it until an EPA approval is obtained. Ford has tightened the quality control on the suspect sensors to attempt to mitigate immediate problem child trucks. I have no information to share on GM's progress. I just do not know.
I hope this helps
Regards
