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2021 Silverado TB 5.3L.  

 

Bought with 13 miles on it.  When I hit around the 500 mile mark, I noticed that every now and again within a minute or two of starting and driving out of the neighborhood, I would get a flashing SES light.  Sometimes it stays on for 20 or 30 seconds and clears.  Other times I will shut the motor down and restart and all is fine.  It does this maybe once a week.  

 

Never felt the motor misfiring when the light was flashing, and the Onstar does not report any issues with it.  Right now it is just irritating, but as anyone else experienced this and more importantly found a solution?

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Mat, we're guessing SES = Service Engine Soon? Which in your truck would be equivalent to the MIL = Malfunction Indicator Light (aka Check Engine Light). Here's a pic from my 2019 manual.

 

2019 Silverado Manual - MIL.jpg

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He means SEL or CEL. And to Mat, I have the exact same issue exactly how you explain it. Start the truck (usually after it sits for my lunch break) and drive slowly out of my neighborhood and I get the flashing SEL which means the truck is misfiring. On star doesn't see anything but my code reader shows misfires on cylinder 1 and 6. Truck has been at the dealer for a over a week, they say they can't get it to do it. I tell them who cares, you see the misfires when you scan it.... Fix it. I've been under the impression that eventually it will break a lifter or valve spring. Although the dealer says they're seeing weird fuel readings on those injectors.... I've told them I'll come get the truck tomorrow, I'll drive it, it'll do it again and I'm bringing it right back and calling GM and starting the lemon law option or buyback process if they don't fix it. They claim they can't rip the engine apart because there are no parts available. He believes there may very well be a recall for trucks built from 6/20 thru 10/20. We shall see. 

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Mine has the same thing. These are my thoughts on my 2021 5.3l Sierra. Just started this issue a week or so ago. 


I noticed mine at low speed (maybe 10-18mph) after sitting with the engine idling. This is under very hot conditions. 110 plus ambient and high under hood temps. This is just staying at this speed in the neighborhood. 
 

One thing I have changed was fuel brands. I was using maverick branded gas 88 octane. I changed back to Exxon Mobil after running the maverick fuel fill almost completely empty.

 

I haven’t had enough time to check it completely but I’m wondering if maybe too high alcohol content or RVP fuel. You never know what you’re getting. 
 

maybe gm has the misfire algorithm too sensitive? Also I’m not sure what speed the skip fire (dfm) starts to work?

 

as of today the light has not come back on. So as a first change, maybe run the tank empty snd switch to a top tier fuel or at least a different brand  

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21 hours ago, Big Bopper said:

Mine has the same thing. These are my thoughts on my 2021 5.3l Sierra. Just started this issue a week or so ago. 


I noticed mine at low speed (maybe 10-18mph) after sitting with the engine idling. This is under very hot conditions. 110 plus ambient and high under hood temps. This is just staying at this speed in the neighborhood. 
 

One thing I have changed was fuel brands. I was using maverick branded gas 88 octane. I changed back to Exxon Mobil after running the maverick fuel fill almost completely empty.

 

I haven’t had enough time to check it completely but I’m wondering if maybe too high alcohol content or RVP fuel. You never know what you’re getting. 
 

maybe gm has the misfire algorithm too sensitive? Also I’m not sure what speed the skip fire (dfm) starts to work?

 

as of today the light has not come back on. So as a first change, maybe run the tank empty snd switch to a top tier fuel or at least a different brand  

 

BB, exactly the same as mine. Got the truck back today and then leaving work it flashed again. Drove straight to the dealer. They can't see anything but the code P0300. They ordered an injector for cylinder 1, we shall see. Makes sense because if it was a vlave spring or lifter it would be constantly misfiring. 

 

 

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Yes I am referring to the check engine light.  The build date of my truck is Mar 2021.  I have not had the issue in over a week.  Fuel wise I normally use BP or Shell 87 octane.  She is due for her first oil change so for ****** and giggles I'm going to take the filter apart and see what I see.  Sooner that later I am going to get a Pulsar so I can halt the DFM and see if that's a contributor.  Those who have taken theirs back to the stealership, let me know how the repairs work out.  

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As mentioned above, after running the fuel tank almost empty, then refilling at a different brand station,  have gone one week or more without a misfire code.

 

Did go to the dealership so they could pull the history on this. Just the P0300. 
 

I believe fuel related. Make sure to run the tank empty. I tried refilling a couple times (to top off) previously and it didn’t seem to fix it. 

Edited by Big Bopper
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  • 2 weeks later...
Posted (edited)

Found this on a competing site:

this is a “too sensitive” misfire calibration issue as mentioned above. 
 

PIP 5809 

 

2020 and 2021 5.3l misfire

 

bulletin with revised calibration to follow

Edited by Big Bopper
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Update...

At the stealership to have the issue addressed.  Apparently there is a software update which was released on 7-5-21 to address this flashing MIL light with no misfire.  GM was allegedly aware of it and needed to tweak the PCM software.  

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I had the same problem with my 2021 Sierra 1500.  It will show the flashing CEL about once a week for a few weeks, go off and then it went solid.  I took it in and they said it was problem with the lifters, which seems pretty common with trucks built between like September of 2020 and March of 2021. They replaced the right bank of lifters, and gaskets and bolts and sealed it up again. Changed the oil and flushed and refilled the coolant.   I got it back and it ran great for about 2 weeks, now just today the CEL came back on again.  Incredibly frustrating.  To have a brand new truck to have less than 3,000 miles on it and have this kind of major engine failures.  I don't think it has anything to do with fuel, but poor quality parts.  The service receipt said misfire on #4 cylinder due to failed intake lifter and bent push rod. I have always had F150's, and went with an almost $60K GMC this time and very disappointed.  I hope you can get your issue resolved.  I am heading back to the dealership again in the morning.  Now they will probably replace the left bank of lifters.       

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