2021 Sierra 1500 AT4 issues

Frustrated Chad · August 11, 2021

On 8/9/2021 at 3:22 PM, Rhino83 said:

Cel was on for 2 days and then off. Drove all last week with no cel but made an appointment to have it checked out again. Dropped it off today and they are looking at replacing the ecm since they updated it last time, but truck is running fine. Still tripping the p0300 code so no changes there. Luckily got a loaner to drive which is a Buick envision lol but at least at not walking. Will update when I get the truck back and let you know what they did.

I have driven so many loaners I could be an expert on other vehicles not to buy. Lol the most comfy was the enterprise rental they had to get me - 21 Tahoe. The gmc 21 acadia was nice and sporty/peppy (v6) both way better than the envision and a smaller one I think. Truck has been in shop since last Tuesday. No update yet. Did hear from the head tech/ mechanic they are going to offer me an additional extended warranty for the motor. Not sure how long though. If it happens again after this time we are getting a lawyer. I will be done, sad but done!! I love the truck but can't drive something I don't trust.

John Mcrae · August 21, 2021

On 4/9/2021 at 6:01 PM, Leslie Politron said:

Hi. I bought a new 2021 AT4 March 5. 20 miles on it. Drove home from the dealer (4 miles) and the next time I turned it on, CEL and OnStar diagnostics emails me to take it to the service department. They say they reset MAP sensor and send me on my way. Later that day, same thing happens. I take it back in, they say MAP sensory needs replacing. They had it almost 2 weeks waiting on the part. After they replaced it, everything went fine for about 1200 miles and then I get blinking CEL for about 30 seconds then it stops. Next day, blinking CEL for a minute or so, and then it turns solid. I took it back to the dealer and they say the only code pulled was P0300 misfire. They have no idea what’s causing it, and quite frankly I’m pretty fed up at this point. They’ve had my new truck longer than I have in the month I’ve owned it. Has anyone had something similar happen?

I'm in the same boat as you. Same code and the first parts they changed were the lifters, only had 1600 miles on it. Now it's back in the shop and they don't know what the problem is. Just throwing parts at it. Very dissatisfied with the product and dealership won't swap it for a new one without paying at least 5000.00 more. Are you kidding me. May have to shame this dealer into a deal that works for me.

Frustrated Chad · August 21, 2021

Latest update. Truck was in shop for 3.5 weeks. Think it was being used as a guinea pig by the GM engineers. App could not connect to it the whole time. Said there was something plugged into the diag port. Picked up today. Told to drive regardless of cel coming on. Per fm engineers. My karen(used to be a karen in her old days, not like the ones you see today but didn't take sh@t!) LOL we requested in writing that it was ok to drive with cel on. Denied. Told them we have lost faith in vehicle. I don't trust it if I have to travel for work. Mentioned buy back and lawyers. Got to see the dealership GM rep. Verbally agreed no issue if l

Cel comes back just keep them updated. Agreed. They are going to ask gm Corp to give us 72/100k for warranty. Plan b is if issue is still not resolved in a few months, vehicle swap basically. So we shall see how this goes. Just not looking forward to possibly getting lawyers engaged. Have me and the boss some piece of mind. As it stands we have had the truck in our possession 50%of the time since March. Want reviews on other vehicle models got me up. Acadia, numerous buicks, even a Tahoe that was an actual rental. Truck mfg date was last year so I think it was worked on by a mechanic building it with covid. Lol truck is sick just like the world today!

kmeleon · August 22, 2021

Guys, check out my thread. Same stuff. I can pretty much make the light go off at will at this point.

Rhino83 · August 24, 2021

Sorry for the delay since my last post on August 9th. Update as of August 24th. When I took it in, on the 9th, they were discussing replacing the ECM or doing another update on the ECM. Come to find out, did neither. Was told the ECM update that was done was for 5.3 V8s without the 10 speed transmission and that GM was working on an updated ECM software for the 10 speeds. Have not had a CEL since July 30th so fingers crossed my worries are over but still guarded. I'm approaching 3K miles so we will see. Service Tech even showed me the bulletin about the updated ECM software regarding 10 speed transmissions.

Frank 2021 · September 22, 2021

[2021 GMC Sierra 1500 AT4 - 5.3L ECOTEC3 V8 W/DFM - currently @ ~3676 miles - purchase NEW this past May 30, 2021]

After the first CEL occurring within two weeks of purchase (see previous comment on page 1 blaming old winter grade fuel) I have driven this truck all summer long (having put premium gas in once or twice shortly after first servicing) with several trips to the beach (including 4wd on the beach) no issues ... but a second CEL occurred two weeks ago (first week of Sept) after a long idle in line for a child pickup after school. It disappeared on it's own a day or two later. Just had it serviced along with another issue where my passenger window would roll back down after I rolled it up. (Sidenote: I did get a base model 2018 Silverado as a loaner but I ended up getting the truck back same day. - Better loaners were promised me by the sales manager after some dealer errors on the purchase day. Not sure that Silverado qualifies, but I digress.)

Written on the service order was the following:

"... DTC P0300 with cylinder 1 & 6 misfire counter history at 130 and 232 misfire counter and number of other cylinder with small amount of misfire counter history"

Since the CEL was no longer on they also documented this:

"No misfire detected ... Recommend reprogram ECM with latest calibration and relearn crankshaft variation Doc ID#5869744"

I don't seem to be getting the quite the same feedback from the technicians as some of the others here, not sure if that means they are being coached to not say it but I guess I'll see how long this "fix" will last.

James Goodin · June 27, 2022

Took my 20 AT4 to service dept due to heavy stuttering. Said that’s what the 10speed tranny does. I said yeah til it gets me killed in traffic. Took back a 2nd time and they want to replace the ECM. But it’s on back order with no eta and they won’t give me a loaner. Only 20k miles. Really frustrating!!