p0300 misfire code

drivereye · March 24, 2020

New truck back at dealers. I have owned it a week and a half and most of that was in the shop for the shift out of park issue. This time it is a flashing engine service light that happened at 100km/hr. I am not sure how long, as when I noticed it, it stopped. Checked the code when I got home and it was p0300. Dropped it off at the dealers and they ran it, checked it, called it in, cleared it and shrugged their shoulders. cylinders 3 and 8 showed a history of misfires. Suspect a faulty dynamic fuel system, but not sure until that throws a code.

hopefully is was a random once only, but I am losing my confidence to be driving anywhere remote.

Michael Ruch · May 31, 2020

On 3/24/2020 at 3:14 PM, drivereye said:

New truck back at dealers. I have owned it a week and a half and most of that was in the shop for the shift out of park issue. This time it is a flashing engine service light that happened at 100km/hr. I am not sure how long, as when I noticed it, it stopped. Checked the code when I got home and it was p0300. Dropped it off at the dealers and they ran it, checked it, called it in, cleared it and shrugged their shoulders. cylinders 3 and 8 showed a history of misfires. Suspect a faulty dynamic fuel system, but not sure until that throws a code.

hopefully is was a random once only, but I am losing my confidence to be driving anywhere remote.

I have the same problem. Did they fix your problem?

GMCustomerService · June 4, 2020

Hi, Michael. Have you had the opportunity to bring this to the attention of your dealership? If not, we are more than happy to connect with them on your behalf. To get started, please send an email to [email protected] ATTN: Forum Username/GM Trucks with your contact information, VIN, brief description of your concern, and preferred dealership. We look forward to hearing from you. To learn more about GM's privacy policy, please visit http://bit.ly/2h3ZUnC.

Aleigha W.

SAVA6E · February 23, 2021

OP- did anything come of this? My 2020 Sierra started flashing the CEL on two separate occasions and it also had P0300 codes on all cylinders. The dealer read the codes but since it wasn't currently acting up didn't act on anything. So far I have not noticed any difference, even when the CEL was flashing.

Thejet07 · February 23, 2021

I had the same issue as well. Not sure if these trucks are finicky with gas but I had the flashing cel on 2-3 occasions. I switched gas stations and ran premium for a bit. I’m back to 87 and I haven’t had the code come back yet(knock on wood). One time was on the highway and the other were switching from reverse to drive if I recall correctly. Like you said, didn’t feel a difference in the car when it happened.

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kmeleon · February 24, 2021

Just had this happen to me again this morning. Last time was at 1300 miles on the clock.

At 1300 miles is started flashing the CEL under light acceleration at about 20-25mph... let off the gas and the light went out... hit the gas lightly again light started flashing again, pulled over and turned the truck off. Started the truck, drove off and no issue from there. I took it to the local dealer West of me and they hooked it up to the Tech2 and found P0300 (generic misfire) but that usually will be accompanied by a p0301-p0308 to call out the cylinder that misfired. No such luck. So they sent me on my way and I didn't have another light until today.

Fast forward to today (2050 miles on the truck), remote started the truck for warm up and left about 15 minutes later from my house. I got a couple 1000 ft and the CEL is flashing, doesn't matter on the gas, off the gas...it's flashing. So I pulled over and shut the truck off. Start the truck, no issues going to work.

Luckily I have an appt tomorrow (at a dealer East of me this time, wasn't thrilled with the lack of effort on the West dealer's part) for my On-star/Sirius unavailable message that pops on my screen every time I start it up. Oh, and my drivers side temperature readout on the climate knob has a bad segment that won't display for about 10 seconds until it warms up a bit.

This is getting old.

Thejet07 · February 24, 2021

If it’s flashing and you can, go straight to the dealership so the could get the active misfires. If you shut it off and wait they just get the p0300 code and can’t see the misfires in real time.

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kmeleon · February 24, 2021

1 hour ago, Thejet07 said:

If it’s flashing and you can, go straight to the dealership so the could get the active misfires. If you shut it off and wait they just get the p0300 code and can’t see the misfires in real time.

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I'm not questioning you and this would explain why they couldn't get the actual cylinder misfire code but why would GM not store the code? The chances of (A.) me having time to drive straight to a dealer and (B.) them just taking my truck in to scan it at a moment's notice seem slim to none.

Thejet07 · February 25, 2021

If you’ve had the problem before they will know and scan it. Takes two seconds and usually the service writer will do it. So no need to wait for tech. But yeah, totally a pita. I don’t get why the codes aren’t stored either

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kmeleon · February 25, 2021

Yes, they can do it quickly but the problem is, the last service writer came out with an overpriced MAC scan tool that is worth $20 and couldn't even get a code off of it. She wanted to send me on my way but I then had to kind of force the issue to get them to take it in the shop and hook the Tech2 up to it. Then they found the p0300 but nothing else. I also had On-star do a scan at the time it happened (but after the light went out and I had shut the truck off) and they couldn't see anything either.

We'll see what happens today at my appt.

Thanks for the info.

Thejet07 · February 25, 2021

Next time don’t shut the truck off and turn it back on

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kmeleon · February 25, 2021

Right, but my on-star trial is up so they're no use now.

kmeleon · February 26, 2021

So the dealer found p0300, p0301 and p0306. So misfires on cylinder 1 and 6, about 22 of them to be exact. They're blaming it on old gas/covid, blah blah. They told me to use toptiergas.com to find a station that GM recommends....Costco is on there as a recommended filling station in my area....it's the only gas I've put in this truck so far.

So I'll continue to report on here and to the dealer if it misfires, I finally ordered a new OBD code reader because I forgot to pull the old one out of the 07 Avalanche when I sold it. So at least I'll be able to read the codes and keep track if they happen to pop again.

Dissappointing.

Thejet07 · February 27, 2021

I’ve read it’s pretty common with these trucks. Probably is crappy gas. Try 91 or 93 for a few fill ups and see if it throws a code again. At least it will rule the gas issue out

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