2021 GMC SIERRA 3500 Engine Problems

Multiple instances of diesel engine emissions system parts and software failure. While driving, towing or not, the DIC would randomly display a message that the DEF level is low and reduced speed will occur in x-amount of miles and that mileage would then begin a visible countdown on the DIC, sometimes much more quickly than the actual speed I was traveling. In other words, it might at first state 500 miles remaining, but then be counting down from 500 miles by one mile per second of time, or faster. Each instance, I would park and attempt to refill the DEF tank, only to discover that the tank is already full or near full. My truck’s DEF tank has now been replaced twice under warranty with the latest tank being installed at only 35,460 miles on the odometer. During the latest replacement, the technician also diagnosed and replaced the electrical wiring...

The throttle body gets stuck wide open after the eninge gets up to operating temperature, it will give some warning with the throttle like on off throttle use and no codes show up at all. The risk of everyones is in extrem DANGER. The break are to soft and well not stop unless you put both feet on the break pedal down to the floor. Tranismission can NOT figure out what gear it needs to be in way too many gears and horrible fuel mpg for the 6.6L Duramax L5P. None of the GM dealership will look at the truck unless there is a code or it is happening right there when they look up the trucks VIN.

•The diesel exhaust fluid heater is a faulty component in the system, there is a back order on the part with no ETA • My pickup only does 55MPH right now and soon to do 5MPH you cannot drive on a public road doing 5MPH •There is thousands of other people having the same exact problem! •The DEF light is illuminated on my dash along with the check engine light, when you diagnose the error code it comes up with “P20C1 Reductant Heater C Control Circuit/OPEN”