Check engine light started flashing then stopped. P0300

Bigfoot98 · July 6, 2021

2020 Silverado L84, 12800 miles.

Today on the highway going about 80mpg and letting off the throttle a little the check engine light started flashing then stopped, came back on while getting off the ramp flashing 2 or 3 times then went away. No messages on the dash or reduced performance, no new knocks ticks or vibrations. Using Shell 87 for fuel. No onstar alerts either, I have gotten 1 for the airbag system when the steering wheel bag was replaced a while back(I hit the horn too hard on the side and broke the horn switch and mounting bracket while avoiding an accident).

Anyway

Went to the dealer and they pulled P0300 Random/Multiple cylinder misfire detected Failure code:00 Status: Test Failed since code cleared

No active codes are noted just stored

They said without diag, obviously, they can't point at any one issue. They said if it's not doing anything in front of them the probably can't find anything anyway but I am free to let them look at it later if needed.

My plan is as per their recommendation to wait and see if it happens again, light comes on and stays, messages appear, or any performance or other concerns are noted.

My thoughts are that it was probably just a glitch with the DFM system and PCM not agreeing on what cylinder was supposed to be firing and when.

Put the truck thru its paces and it takes off smooth and nothing seems wrong with it.

Knock on wood it stays that way.

Anybody have something similar happen?

jerryz06 · July 7, 2021

I had that happen to my 2021 GMC Sierra SLT with 5.3. It happened 3 times so far, each time it flashed for a few seconds and the blinking light shut off when i got on the gas.

The first time around 1,000 miles 3 weeks ago (engine was warm) and the last two times it happened this Friday ( engine warmed up) and Tuesday morning (cold engine) around 1,400 miles. It runs and drives normal, the dealer said they cant do anything since the light is off and it makes no weird noises and cleared the code history.

They had a couple of trucks come in 2 weeks ago due to misfires and rough idle and all of them filled up with gas at costco, i also only put 87 at costco for mine, ill try different gas this time.

I always shut off the start stop every time i drive it, i wonder if it is a glitch in the computer. i'm debating installing the PULSAR and see if it continues to happen after i try new gas first.

Jerry O

OGreatOne · July 17, 2021

check out this link

Engine Misfire Detected without Drivability Concerns – TechLink (gm-techlink.com)

Bigfoot98 · July 17, 2021

12 hours ago, OGreatOne said:

check out this link

Engine Misfire Detected without Drivability Concerns – TechLink (gm-techlink.com)

Thanks for that

Transient · July 25, 2021

I just had a similar issue tonight, but I have the L87. Driving southbound on I-15 from Vegas, headed to San Diego. While dropping down into Baker, CA, cruise control was set at 78 mph. Time was approximately 10:30pm. Outside temp was 95°. AC was off because sunroof and rear window were open. Engine temp was normal, oil pressure was normal, and trans temp was 147°. Just me in the truck, and no payload nor trailer. Southbound I-15 dropping into Baker, CA is a steep decline. Iirc, 6% for several miles. The mountain pass parks at over 4,000 feet, and Baker is below 1,000 feet. Due to no reportable issues with the truck I continued to drive, but immediately closed the windows, turned on the AC, and pressed the OnStar button. OnStar ran a check for codes and didn't find a single one.

One thing to note: this is the 2nd time I've had an issue with the truck on this exact same stretch of highway, and both times it was 90°+ outside. Cruise is always set at 8 mph over the posted limit, and it only happens while going downhill. I've made this same trip several times over the last year, but outside temperatures were much milder, and nothing happened during those trips.

Imo, no point in taking the truck to the dealer since they won't find any codes to help them. So I guess that just leaves me to being curious what everybody thinks. If it's happening to both the L84 and L87, then it's probably associated to something common for both engines.

msween313 · July 26, 2021

I had the same problem with my 2021 1500 Sierra AT4 5.3. Bad lifter arms which are on backorder. Truck only has 3,600 miles and now it sits at the dealer.

Bigfoot98 · August 13, 2021

Happened again today, same part of the highway, going 83 and coasting, temp is 93 feels like is 100 with no breeze or clouds, similar to the first time it did it.

stayed on for about 30 seconds but didn’t seem sluggish or reduced power and no onstar alert. 14400 miles.

May take it in and see what they say this time, idk yet.

kmeleon · August 14, 2021

21 hours ago, Bigfoot98 said:

Happened again today, same part of the highway, going 83 and coasting, temp is 93 feels like is 100 with no breeze or clouds, similar to the first time it did it.

stayed on for about 30 seconds but didn’t seem sluggish or reduced power and no onstar alert. 14400 miles.

May take it in and see what they say this time, idk yet.

My truck has flashed the SEL light about 15 times in 5800 miles. Always once truck is warmed up for the day, always around 0-20mph and usually after making a turn out of my development or leaving my work. Always light on the throttle when it occurs. Interesting thing though, I decided to drive around in L9 for a month and it never went off once. It always does it when in D.

If you can get it to flash the light twice in a row it will throw a solid SEL light. But it has to be within a few engine warm-ups or miles. Mine always seems to do it after sitting for 30min-3hrs and then within 1/4 mile of leaving wherever I am. It's never done it while driving at speed. Also, I absolutely believe it's related to DFM hence why when driving in L9 it doesn't flash the light.

I took it in for the 5 or 6th time this past Thursday when the light was solid, they openly admit they don't know what to do with it and neither does GM's engineers. I called gmc Thursday night to see what they're going to do about this. I'm due a call back from the investigator by Wednesday next week. I'm pushing for 100k engine warranty if they want me to keep it.

Bigfoot98 · July 12, 2022

Well figured I would update this again

Happened today, 26260 miles

same part of the same highway going 75-80, 96 degrees and AC on full blast.

Slowed down and it would go away. Stayed on for 30 seconds or so and stopped

no codes active.

Maybe I will have it reprogrammed, idk.

kmeleon · July 18, 2022

On 7/12/2022 at 4:43 PM, Bigfoot98 said:

Well figured I would update this again

Happened today, 26260 miles

same part of the same highway going 75-80, 96 degrees and AC on full blast.

Slowed down and it would go away. Stayed on for 30 seconds or so and stopped

no codes active.

Maybe I will have it reprogrammed, idk.

Mine was fixed by a CPU update back in 10/21. Hasn't done it since. Make sure they follow the directions to the T provided in the bulletin.

Bigfoot98 · July 18, 2022

2 hours ago, kmeleon said:

Mine was fixed by a CPU update back in 10/21. Hasn't done it since. Make sure they follow the directions to the T provided in the bulletin.

I just stopped by the dealer on my way home from work and talked with the SA that I actually trust since it did it for the fourth time. She pulled the codes and found the p0300 again.

We looked at the tsb 21-na-154 and setup the appt in a few weeks, obv they’re gonna do a diag first then go from there but hopefully that fixes it.

it’s supposed to be brutally hot for the next few weeks so it’ll probably happen a few more times

And there no loss of power or knocking/ticking so that’s good news.

Bigfoot98 · July 21, 2022

Another update

saw an alert on my onstar app for engine, transmission, stabilitrac, abs, and airbag

called onstar and no codes are showing on their diag report, also no cel.

decided to get a BlueDriver obd scanner overnighted by Amazon, my OBDLink was showing no codes at all, BlueDriver pulled the p0300, as well as u0102, u0131. u0140 and u0403.
found another tsb that has all but the u0403 on it. Based on the code names I don’t think it would be that far of a leap for it to set as well. 21-na-149 engine wire harness chaffing

calling the dealer in the am, moving the appt up to asap from in a few weeks when it would be convenient. Figures

I’ll keep this updated for anyone that may be going through something similar, especially since there’s 4.2k views as of this post.

Edited July 22, 2022 by Bigfoot98

Bigfoot98 · July 25, 2022

Just had 21-na-154 performed

Dealer said that the U codes weren’t able to be retrieved on their scanners, just the p0300 and the codes for the led turn signals

They think it may be an issue with the BlueDriver, however they did see a long history of misfires being recorded.

Chief Paw Paw · April 7, 2023

Hello to the group. I'm new here and was hoping I could get some idea as to what happened on my 20 Sierra SLT. I was on the interstate and passed going around 80 mph. Right afterwards I was back to 75 and suddenly the CE light started flashing and the dash had flashing message "Service Parking Brake". This went on for about 30 seconds and disappeared. I could feel some subtle jerking as I pulled off at the next exit. Felt like the trans (10 speed) was searching for a gear. As I began to put on the brakes there was more profound jerking like the parking brake was pulsing.
Everything on this truck is electronic including the parking brake.

I have an OBD tester and it pulled codes P0300 (Random, multiple cylinder misfire), U0401 (Invalid Data Received From ECM/PCM "A"), U0131 (Lost Communication With Power Steering Control Module), U0102 (Lost Communication with Transfer Case Control Module) and U0140 (Lost Communication With Body Control Module).

I shut the vehicle off and checked under the hood but everything still looks pretty new under there. Checked for loose wires and didn't detect any. I went directly to the dealer and they said they would need to have their engine specialist diagnose it but couldn't get me in until 3/23. The truck ran much better on the way to the dealer and now runs like nothing ever happened. Full power and smooth. WTH!! Any ideas folks? I'm not sure anyone has experienced this exact issue but would appreciate any ideas. Thank you

Update: the issue above happened on 3/8/2023. The truck was running normal until 4/3/2023 when the CE light started flashing again and this time the code was P0308 (cylinder 8 misfire) On shortly thereafter the light went out and ran normal again. I took it to the dealer who performed diagnostic and said the issue was fouled plugs. They replaced the plugs and all seemed fine until yesterday the CE came on again with a P0300 and runs like crap. Runs worse than ever. This seems to be a widespread occurrence in these vehicles. Has anyone had this resolved?