Check engine light started flashing then stopped. P0300

Chief Paw Paw · April 7, 2023

5 hours ago, crj19 said:

I had all of those issues weeks before my lifters went and then bent a pushrod.

My check CE light stayed on for about 24 hours. went off yesterday. My appointment at the dealer was today. They stated the code was recorded but didn't store any history so they can't diagnose. Recommended I leave it with them for a while. I told them I will bring it back when it happens again and they can keep it until fixed. Sorry about your pushrod issue. These trucks cost way too much to be having these problems.

GMCustomerService · April 12, 2023

On 4/7/2023 at 11:21 AM, Chief Paw Paw said:

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?

This is certainly not what we like to hear, Chief Paw Paw. Please know, customer satisfaction is extremely important to us. Our team would be more than happy to take a closer look into the concerns with your 2020 GMC Sierra. To do so, please send an email to [email protected] with ATTN: Chief Paw Paw/GM Trucks in the subject line.

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JK4090 · August 21, 2023

On 4/7/2023 at 11:21 AM, Chief Paw Paw said:

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.

Having similar experiences to others on this thread with the dealer not finding the correct fix. Before it was the flashing CE light going away and P0300. Now I experienced this exact same thing with the "Service Parking Brake" and subtle jerking slowing down and coming to a stop. Twice now within a week.

Anyone have new updates to resolve the issue(s)?

Edited August 21, 2023 by JK4090

Chief Paw Paw · August 22, 2023

8 hours ago, JK4090 said:

Having similar experiences to others on this thread with the dealer not finding the correct fix. Before it was the flashing CE light going away and P0300. Now I experienced this exact same thing with the "Service Parking Brake" and subtle jerking slowing down and coming to a stop. Twice now within a week.

Anyone have new updates to resolve the issue(s)?

Allow me to provide an update.

I took my truck back to the dealer and let them know the new, very expensive plugs they installed did not correct my problem as the CE and multi misfires were still occurring. BTW, When the changes the plugs I had dealer perform full injector cleaning.

The dealer stated they would need to inspect the truck. I waited 2.5 hours and the dealer said they couldn't find anything wrong. When I pulled out of the lot the truck was running better than ever. When I took it in for my next oil change I asked the service manager what the tech did to the truck. He said they did nothing as they found nothing to service. I told him I disagreed with that response but went on my way. It wasn't long before the CE came on again and, yep, another multi misfire but I haven't seen the "service parking brake" warning again. Another thing I noticed is the auto stop feature and the AFM doesn't seem to work anymore since I was last at the dealer. Well, i still get the CE's and random misfire codes. Got one last week. I have all of the data sheets generated by OBD readers for each incident. I notice a ticking in my engine last week as well. I have an appointment at the dealer for oil change, tire rotation and transmission service. I will discuss my ongoing issues with the service manager and see if he can help. I love my truck but the many thousands you have to shell out to own one and then have to deal with all of this and I hate to say it, but I don't have confidence my engine will last much longer.

Flores2020 · October 15

Was there ever a remedy found for this? My 2020 Trailboss LT just started doing this at 72k miles. At first i thought it was the battery due to this issue and low horn chirp, so i changed battery. Then i was cruising fine at 75 and the service esc, parking brake, and CEL flashing happened. I went to an oreillys to read codes due to dealership being closed. It came out at P0300. Truck was running fine: no rough idle, temps and pressures good. I disconnect and reconnected battery to try and reboot the computer. It took off my CEL and truck ran fine as ever. 2 weeks later same thing happened. My dealer says no engine light, no diagnostic. I then thought of maybe foul spark plugs, dirty injectors, etc. If dealer cant help im thinking of taking it to a performance shop to flash computer and deactivte dfm/afm and have v8 full time.

asilverblazer · October 15

6 hours ago, Flores2020 said:

If dealer cant help im thinking of taking it to a performance shop to flash computer and deactivte dfm/afm and have v8 full time.

This won't fix a miss fire.

Its an old thread, but there is documentation to visually inspect for other problems that the truck can detect as a miss fire that are nothing of the sort. It listed items such as tire out of balance, accessory drive belt problems, road imperfections, bad motor mounts, etc. The point being that the knock sensor can 'feel' some abnormal vibrations and assume it is an engine miss fire.

Flores2020 · October 20

On 10/15/2024 at 2:50 PM, asilverblazer said:

This won't fix a miss fire.

Its an old thread, but there is documentation to visually inspect for other problems that the truck can detect as a miss fire that are nothing of the sort. It listed items such as tire out of balance, accessory drive belt problems, road imperfections, bad motor mounts, etc. The point being that the knock sensor can 'feel' some abnormal vibrations and assume it is an engine miss fire.

Now that you say road imperfections, the roads ive been driving on have been ****** and the times these problems occured were during stop and go, stop and go driving in cities