P0300 on 2020 Sierra 5.3

Chief Paw Paw · March 14, 2023

Hello to the group. I am hoping I can get some idea as to what happened on my 20 Sierra SLT 5.3. I was on the interstate cruising at 75 and sped up to 80 to pass a slower vehicle. Right afterwards I was back to 75 and suddenly the CE light started flashing and the dash stated flashing the message "Service Parking Brake". This went on for about 30 seconds and disappeared. I could detect a change in performance. 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 plugged in my 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

vucelick · March 15, 2023

You will likely get better action to your post on the light-duty forum. This is the HD forum and none of the HD trucks have the 5.3 motor.

https://www.gm-trucks.com/forums/forum/236-2019-2023-silverado-sierra/

64BAwagon · March 15, 2023

My guess would be that its an electrical malfunction of some sort.

Your codes are varied and to me indicate a ground or power issue. The first thing I would do (always start with the cheap and easy first) is to remove the battery cables and clean and tighten them. From there inspect them very carefully and assure that the connections in the underhood electrical center are tight and that nothing has a rub through or looks compromised.

I replaced the battery on my Cruze a little over a year ago. I cleaned the battery cables during the replacement and went through all the ground connections and cleaned them and tightened everything. A few weeks ago I got some crazy generic code (dont recall which one) with a CEL. I looked at the connections on the battery and they were tight enough that you couldnt turn them but when I put a wrench on the ground side it didnt seem real tight. I try not to crank them down in fear of breaking the connectors but after removing it. cleaning it and tightening it again the issue was gone and has not returned. Modern GM vehicles are crazy sensitive to ground issues. Time to get out the 10mm socket and wrench and a wire brush.