Flashing Check Engine Light - Followed by Rough Shifting

[MarkAlbert1219]

Apologies in advance if there is a thread for this, searched through 10 pages of topics and didn't see anything, so here goes:

 

2018 Silverado LT

5.3 

 

In May of 2019 got a vibration accompanied by a flashing check engine light which I figured was a misfire or stuck valve. That lasted about six seconds and never had an issue following that. 

 

Noticed this fall (2020) whenever going at highway speeds, each time engine switched over to V4, I'd gat a strange humming noise that would start faint, and get louder. As soon as it went back to V8, no noise. Took to dealer and they couldn't replicate the issue because they obviously aren't road testing the truck doing 70mph, and because of COVID, I wasn't allowed to drive it with a tech in the truck on the highway in order to replicate it. 

 

Tonight (Feb 2021) truck was driving fine, and got a flashing check engine light again, but no vibration / misfire, that lasted about 15 seconds. Just as I went to pull over to shut off/restart the light stopped flashing. I was a mile from home and figured get it home, evaluate later. The rest of the drive however, it shifted rough both up and down through at least 4th gear. Going from 2nd to 1st feels like I'm being rear-ended. 

 

Taking to dealer on Monday, but was curious if anyone has had an experience like this in the past? 

[JimCost2014]

17 minutes ago, MarkAlbert1219 said:

Apologies in advance if there is a thread for this, searched through 10 pages of topics and didn't see anything, so here goes:

 

2018 Silverado LT

5.3 

 

In May of 2019 got a vibration accompanied by a flashing check engine light which I figured was a misfire or stuck valve. That lasted about six seconds and never had an issue following that. 

 

Noticed this fall (2020) whenever going at highway speeds, each time engine switched over to V4, I'd gat a strange humming noise that would start faint, and get louder. As soon as it went back to V8, no noise. Took to dealer and they couldn't replicate the issue because they obviously aren't road testing the truck doing 70mph, and because of COVID, I wasn't allowed to drive it with a tech in the truck on the highway in order to replicate it. 

 

Tonight (Feb 2021) truck was driving fine, and got a flashing check engine light again, but no vibration / misfire, that lasted about 15 seconds. Just as I went to pull over to shut off/restart the light stopped flashing. I was a mile from home and figured get it home, evaluate later. The rest of the drive however, it shifted rough both up and down through at least 4th gear. Going from 2nd to 1st feels like I'm being rear-ended. 

 

Taking to dealer on Monday, but was curious if anyone has had an experience like this in the past? 

My guess would be your torque converter is failing, becoming a very common issue in the early K2's.

 

The flashing CEL is kind of a mystery, could be a failing lifter, hope you do not have multiple issues going on at once.

Edited February 21, 2021 by JimCost2014

[Lsgun1]

Pull codes to start

[MarkAlbert1219]

1 hour ago, Lsgun1 said:

Pull codes to start

Only code pulled was P0300 which is a misfire code. 

Still stuck on the rough shifting, but it seems awfully coincidental that the rough shifting started the same time the misfire code was thrown. 

[evad]

idk but it sounds like electrical issues ..maybe a bad pin connector or green crusties ...just a guess tho

 

[rlcole321]

Is it the 8 speed or 6 speed trans?