Q: There are continuing emission system problems with GMC LML diesel trucks to the point that they have become untrustworthy. These problems can only be addressed at a GM dealer, and if you are in a remote location (think Alaska), you can find yourself stranded for an extended length of time. This website, http://www.duramaxforum.com/forum/2011-lml-duramax-powertrain/193378-calling-out-all-who-had-problems-def-emissions.html, among other sites, provides an ongoing description of the problems that are being encountered. GM seems to be out of the loop. I suggest you publish this in Truck Trend so prospective GM Duramax buyers are forewarned.

A: We needed to clean up diesel engines to meet emissions requirements, and here's what we got. The key to the system is something everybody wanted to avoid: the add-on of a mandatory task for truck owners , DEF (diesel exhaust fluid). Now diesel drivers have to fill up (and pay for) DEF on a regular basis. The system as a whole is referred to as SCR (selective catalyst reduction). And it has completed its assignment by reducing Nitrogen Oxide (NOx) by 63 percent compared with 2010 Duramax-equipped trucks. But, as with most all-new complex automotive systems, it has its bugs.

DEF is 33-percent-ammonia-based urea and 67 percent purified water injected into the exhaust system. Exhaust heat converts DEF into ammonia. When the exhaust and ammonia reach the SCR catalyst, the NOx emissions are broken down. The Diesel Particulate Filter catches and incinerates the soot, and water vapor, nitrogen, and reduced emissions come out the tailpipe. DEF is stored in a 5.3-gallon tank, and you should get about 5000 miles per fill-up. There's no gauge, but a low level message will be displayed on the instrument panel. DEF prices will vary, but it's getting close to about $3 per gallon at the truck stops. If you run out of DEF, truck speed will be limited to 55 mph at the next startup, and steadily downward to 4 mph after that. Yes, there have been a lot of problems with the 2011/2012 models varying from DEF contamination to overly sensitive sensors. There was also a recall on the DEF tanks themselves. You 6.6-liter Duramax owners can expect messages including Exhaust Fluid Range, Exhaust Fluid Quality Poor, Service Exhaust Fluid System or Service Emission System, and/or the MIL. This type of system has been used in Europe for quite some time, and the 2013-and-up models should be showing significant signs of improvement in reliability. Earlier model owners should stick with GM service as they learn the correct fixes and modifications to the new system.


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