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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?

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  • 2 months later...

Yes, same exact vehicle (2021 GMC 1500 AT4) - 281 miles on it, not even two weeks old. Check engine light was on and I took it in. Initial diagnosis was misfiring - waiting to hear more. I heard a ticking sound on the test drive also - unsure if that is related though seemed to be mentioned on another website. Frustrated beyond belief that a new vehicle (that’s basically a 3rd gen) would be going thru this. Bought it for a family trip to & on the beach in less than a week and been customizing it with racks, etc. First GMC purchase and I’m not feeling confident about the brand at all now.

 

FYI - Couple of other sites referencing this issue:

https://gm-techlink.com/?p=13855

https://gm-techlink.com/?p=14363

 

Hoping my techs do their research and they can fix it fast, I’ll be furious if I have to get a rental for the trip. Hope they figure yours out fast too. No new vehicle purchaser should have to go thru this.

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We have had same issues. Purchased mid March 2021 AT4 drove 2 weeks about 700 miles and CEL comes on.  Take it to dealer P0300 code misfire, cleared error and gave back a couple of days later.  Had a week or two and it comes on again cleared again.  Very next day on again.  This time they crack open engine and change lifters, coil, coil wires and some sensor. Drove hour and halfout of town and truck shuts down, towed to shop. Dealer says bad coil wire and software code issue. Beyond frustrated.  Told GM engineers are working to fix software, and to drive with light on, which is quite scary.  Would love to know if others having same issues.

 

 

Rare week it was home. Lol

Screenshot_20210617-190005_Gallery.jpg

Edited by Frustrated Chad
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2 hours ago, Frustrated Chad said:

We have had same issues. Purchased mid March 2021 AT4 drove 2 weeks about 700 miles and CEL comes on.  Take it to dealer P0300 code misfire, cleared error and gave back a couple of days later.  Had a week or two and it comes on again cleared again.  Very next day on again.  This time they crack open engine and change lifters, coil, coil wires and some sensor. Drove hour and halfout of town and truck shuts down, towed to shop. Dealer says bad coil wire and software code issue. Beyond frustrated.  Told GM engineers are working to fix software, and to drive with light on, which is quite scary.  Would love to know if others having same issues.

 

 

Rare week it was home. Lol

Screenshot_20210617-190005_Gallery.jpg

 

 

What engine does your truck have???

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I just got my 21 5.3 back today from flashing SEL light. Throws P0300 code each time. It always seems to happen after it's been run once that day and sitting for 30 minutes to a couple hours. Then once I drive away under light acceleration and speeds around 15-25mph it flashes the SEL light within the first 1/4 mile of driving. 

 

Today i got the truck back at lunch, drove to work and then when I left 3hrs later it started flashing. Drove straight to the dealer and didn't shut the truck off. They said they'd be able to read it and see the snapshot of what happened. Well they couldn't see the snapshot but they're going to order an injector for cylinder 1 since it has a huge amount of misfires. Tech told me the injectors and lifters are junk in this truck. Very disappointing to hear, he recommends doing an afm/dfm delete. But he wasn't sure if there's a dfm delete for the 21's.

 

Anyway, I'll report back once they change the injector. 

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17 minutes ago, Kanon Morris said:

Will a DFM delete be as if the truck never had DFM, or could there be residual issues by virtue of the hardware being present?

My question is, is there such a thing? I know it exists for afm.... What about dfm? 

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37 minutes ago, kmeleon said:

Yes I'm aware of the Range device but the faulty DFM style lifters aren't removed. The lifters can still come apart. 

Ahh, gotcha.  That sort of answers a question I had.  I drove a 2021 elevation 5.3L that did not include the DFM (-$50 on the sticker).  I was curious if the actual hardware was removed, or if that was a software removal.  Sounds like GMC possibly removed the hardware?

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8 hours ago, Kanon Morris said:

Ahh, gotcha.  That sort of answers a question I had.  I drove a 2021 elevation 5.3L that did not include the DFM (-$50 on the sticker).  I was curious if the actual hardware was removed, or if that was a software removal.  Sounds like GMC possibly removed the hardware?

That I'm not sure about. Not sure if they just left the same hardware but no electronics. 

Edited by kmeleon
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Sorry for the late response. Still having issues with random CEL blinking after misfires. I’m at 7,250 miles now. It always happens when driving under 30 mph. 3 times this week already. I set up an appointment at the dealer for tomorrow and they just called and said “gm is aware and sent us word to hold off on any repairing or replacing of parts & they won’t fix or replace anything on my truck, basically they will clear the error codes and send me on my way until gm tells them what to do. She said it’s happening with a lot of Sierra/Silverados right now. I’m honestly losing my patience already. I have so many mods planned out and put on the back burner because I don’t feel comfortable doing them until all of this gets sorted out. Wondering if I just throw in the towel and switch to a different brand truck

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