I have a stupid question. I have a 2015 Silverado HD with about 19,000 miles on it. At the bottom of the gauge cluster there is this little green and sometimes yellow car symbol that comes on and I kept thinking that this was telling me that the diesel particulate filter was being cleaned by the exhaust fluid (Or I think some may call this "regen" cycle) but when I read the manual it said that the DIC would actually tell me it was doing that and I never could find any info on the green car symbol. I then thought that it was telling me I was getting optimum fuel mileage but it is on all the time no matter how I am driving and I have a lead foot. I do also drive slow and watch the fuel economy gauge so I have all types of driving habits. What is the green and sometimes yellow light telling me?