2016 Chevy LML Duramax service exhaust fluid system

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Hi I’ve got a 2016 Chevy Silverado LML Duramax started throwing a check engine light last winter for the exhaust fluid heater it went away when the weather got warmer never really worried about it until recently when we started having cold nights end it through a check engine light for the same thing I did go online and I did order a Bosch exhaust heater yesterday I drop the tank put the new heater in meanwhile as I was still driving it before the part came in it started Throwing A message on the screen that said 65 mph speed limit in 99 miles. I kept driving it and shortly after about 150 miles it said speed limit 4 mph and 75 miles I put the new heater in and I still have the message I did get it to go away but I came right back on and started all over don’t really know what the problem may be Thanks for all the help I really don’t want to take it to a dealer and have a $3000 bill