I bought this used 2012 GMC 2500 Sierra Denali Diesel December 2021. I didn't drive it 3 months and in April 2022 the diesel exhaust fluid light came on and would not go off after refilling the DEF reservoir. Repair was to put in a new DEF injector, fix broken line. Then drove it until November 2022 when same thing happened all over again. This time, GMC (Clason GMC) replaced almost the entire system, (particulate filter, catalyst, heater (basically replace from the engine to the tail pipe) and it still did NOT work. The light kept coming back on, limiting my speed. Finally took it back to my original place of purchase and they repeatedly called GMC and their parts store; put on a 2nd after market catalyst, light STILL came back on. The final solution was to plug in a 1000.00 part to override the DEF system and it has been working.... 1 week.

One diesel mechanic on record told my other mechanic that the 2012 is the WORST for DEF problems.

Absolutely ridiculous! I didn't buy a diesel to spend 8351.74 on DEF problems.

Carried the vehicle to a parts store to see what code was stored in computer, no code in computer. Dash displays, "Poor Def Fluid Quality". Carried to dealer to have service performed under an extended warranty for the DEF issue. Got a call saying there was a code in computer for Nox sensor bank 1. Took truck straight to another parts store, guess what, no code for Nox sensor. I replaced it because dealer wanted $600.00 to replace, thinking they were guessing at what was wrong. I replaced with OEM part for less than $200.00. Same display on dash. Carrying back to dealer this morning to probably take another shot in the ass. Called GM, but they have foreigners answering the phone, and they could give a rats ass if you get taken care of. I advised them that I moved a couple of streets over, but It was the same town, same zip code. The very next time I called, the woman wanted to verify address. She stated street number, and then proceeded to tell me, "Same town, AR.?" I could not believe this. Three calls to GM. They just don't understand the magnitude of my anger, and frustration. This is ridiculous that GM can slow my truck down, force me to spend money, when they know they have, and continue to have from 2010 to now. They are just putting the repair cost on the customer, when they are too incompetent to repair their own truck they manufactured. Whey they do issue a recall, or service bulletin, they will just cover the one part they deem defective, and leave me with the cost of the other parts, "Thrown" at the truck to try to repair it. They suck!

Out of nowhere, a message appears on my dash:

EMISSION SYSTEM REQUIRES SERVICE SEE OWNERS MANUAL NOW 280KM TO 105KM/HR SPEED RESTRICTION

When i look in my owner's manual, i am advised to take it to a dealer. I make an appointment the next morning with the dealership that i purchased it from, on the other side of the city. I check the fuel cap to make sure it's on tight. Ensure it's filled with good quality gasoline, and top off the DEF fluid. Warning still in effect, and counting down to my doom. When i arrive at the dealership, (after the service guy finishes an extended social conversation with his mechanic friend) they appear shocked that this is a diesel engine (though i have bought and serviced it there) as their 'diesel guy' is unable to look at it until the following day. This won't work for me, as I am supposed to be hauling a 5th wheel the next day, and I need this truck to do it.

I contact another dealership, on the other side of the city who can see me immediately. They take it in and shuttle me home. I find out at the end of the day that "all the sensors in the DEF tank are screwed and not working". The only fix is to replace the tank. HOWEVER, they tell me that the HAVE NO STOCK on tanks, and have not heard back from GM as to where or when they can get one. When asked how long this is going to take, I'm told that they could have my truck for 1 - 2 weeks, and it is not driveable. Yes, 1 -2 WEEKS! Really?!

The 5th wheel trailer that i was going to be hauling home after a weekend of camping is now stranded in another province, and i'll have to make a special trip to retrieve it in the coming...weeks?! Thanks GM! You ruined my weekend and caused huge issues for me and my family, on a NEW vehicle. And there is NO STOCK on a part that it obviously an issue on these trucks?!!! Ridiculous and unreliable. Take your truck and shove it.