Dtc code P1098 present related to faulty coolant control valve on 3.0 duramax diesel engiine. This is a known issue with this engine and is supposed to be covered under the 100K mile powertrain warranty. Previously took vehicle into dealership for repair involving replacement of the coolant control valve but was told reprogramming of the ECM was required first step per GM repair bulletin. Reprogramming cost me $195 and was told this was not covered under the 100K powertrain warranty. Now, a few months later, the same issue and dtc code P1098 happened again while driving on freeway at freeway speeds and caused vehicle computer to limit speed of the vehicle which caused hazardous situation in construction zone as was not able to maintain speed of traffic while towing trailer with boat. I also understand that GM has issued special extended warranty related to this coolant control valve in September 2025 which extends the warranty coverage up to 15 years and/or up to 150K miles but I was told at the dealership that my VIN# does not qualify for this extended coverage for some unknown reason?

- Waterford, MI, USA

The engine coolant flow control valve position sensor is faulty. I brought mt truck in to my dealership and I have been waiting for over a month to get the issue fixed because -??the part is on backorder-??. This issue makes my truck sound like a jet engine because it makes the truck think overheating and causes the fan to come on at full blast. After drivinf for awhile it goes into -?? reduced engine power mode-?? which is totally unsafe because it reduces the horse power to that of a lawn mower. It takes about 30 seconds to get from 0-60, so merging onto freeways or in conditions where you need extra speed its completely useless and increases the scenario of being rear ended, immensely.

- Medford, NJ, USA

Tried to accelerate and heard a loud pop and the truck didn-??t accelerate. Pretty much went idle in the middle of the road. The check engine light, the traction control light, and the ABS light all came on. I would press on the gas and it would rev but nothing would happen till a few seconds later the RPM-??s would shoot up and you could tell it was trying to get going but didn-??t very slowly and I would hear a clicking noise every time it was around the second gear. It put my children and myself in danger because traffic was heavy with vehicles going 70+mph merging into one lane. Took it to a dealership and they stated it was the the push rod and camshaft were damaged and all 16 lifters should be replaced and camshaft also. No, the vehicle has not been inspected by any of those except a car dealership and a mechanic. This problem first appeared the day it happened and continued after. Even took it to a mechanic and had all 16 lifters changed and problem still persists. Spent over $6,000 on a brand new truck and it is still undrivable because every time you get in to drive it the cylinder #2 misfires.

- Gillett, TX, USA

On the morning of 1/19/25, my 2021 GMC Sierra 6.2L AT4 went into limp mode heading south on HWY 207 in Leavenworth, WA at approximately 60 m.p.h. Fortunately, I was able to avoid a rear end collision. I quickly turned the truck off in the middle of the road and restarted it with a CEL. When I returned home almost 180 miles away, my local mechanic diagnosed a code P0303 and cleared it. Since, the truck has continued to shutter at various speeds without throwing a code. It is currently at Haselwood GMC in Bremerton, WA being scanned, recorded, and findings set to GM waiting for resolve. I have notes, exact dates, times, call records, return voice mail messages, and dealership personnel spoken to, etc. The dealer-??s lead technician and I were able to replicate the shutter on a road test together on 1/27/25 at 3 p.m. after having driven just 10 miles. During my visit on the morning of 1/30/25, the lead technician stated he has since been able to replicate the shutter seemingly getting worse. I was strongly encouraged by the service manager, service writer, and lead technician their collective -??personal recommendation-?? was to not take the truck back. Haselwood has had the truck since 1/27/25. Still awaiting a response and resolution.

- Seabeck, WA, USA