C7 Misfire P0300 potential fix
Thread Starter
3rd Gear
Joined: May 2026
Posts: 3
Likes: 1
C7 Misfire P0300 potential fix
I purchased my 2017 Z51 a couple weeks ago, noticed a super rare low idle shake but it didn’t happen again on the 5 hour drive back home, Next day the car has a service rear axle prompt, stabilitrack, and a flashing check engine light. Spent 2 days trying to diagnose it tried plugs, wires, coils, acquired a snap on reader which didn’t help much due to the only code being a P0300, (Random multiple cylinder misfire) doesn’t state specifically what cylinder. Couldn’t figure out what was wrong with it so we took it to a chevy dealer and they diagnosed it as a bad driver side o2 sensor. The sensor was driver side right after the headers (1,3,5,7) cylinder bank. Replaced o2 sensor and problem is gone. Posted this to help someone figure out similar problems because i never knew a simple o2 sensor fault could cause such horrible shaking misfires and service lights.
Melting Slicks
Joined: Feb 2018
Posts: 2,172
Likes: 1,041
From: North Texas
I find it hard to believe that a Snap On scanner would not diagnose the bad O2 sensor better than it did.
But once again, you need the right kind of high quality tools and also the knowledge to be able to interpert the data for sucess.
Happy you got it fixed.
But once again, you need the right kind of high quality tools and also the knowledge to be able to interpert the data for sucess.
Happy you got it fixed.
Thread Starter
3rd Gear
Joined: May 2026
Posts: 3
Likes: 1
O2 sensor
Yeah i forgot to mention that i’ve only worked on 5.9 cummins and 90’s toyota 22re’s. So having the scanner didn’t help me much due to lack of knowledge of what to look for. like i said i had no idea o2 sensors could cause that bad of problems in a car, Usually in my experience a bad o2 sensor causes poor fuel economy and CEL not severe misfires. So In my head i kind of had it ruled out.
Last edited by tycececil; May 30, 2026 at 11:40 AM.
Moderator, Tech Contributor
Joined: Sep 2013
Posts: 15,594
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From: Cape Coral, Florida
I purchased my 2017 Z51 a couple weeks ago, noticed a super rare low idle shake but it didn’t happen again on the 5 hour drive back home, Next day the car has a service rear axle prompt, stabilitrack, and a flashing check engine light. Spent 2 days trying to diagnose it tried plugs, wires, coils, acquired a snap on reader which didn’t help much due to the only code being a P0300, (Random multiple cylinder misfire) doesn’t state specifically what cylinder. Couldn’t figure out what was wrong with it so we took it to a chevy dealer and they diagnosed it as a bad driver side o2 sensor. The sensor was driver side right after the headers (1,3,5,7) cylinder bank. Replaced o2 sensor and problem is gone. Posted this to help someone figure out similar problems because i never knew a simple o2 sensor fault could cause such horrible shaking misfires and service lights.
Yes, an O2 sensor can cause a misfire whether the sensor is "stuck" rich or lean...the ECM will either over or under fuel the injectors...if you had a Snap On and the misfires were consistent it should have identified what cylinder or cylinders were misfiring...I had a bad O2 years ago "stuck lean" and it was over fueled and the exhaust stunk...3 out of 4 bank 1 cylinders were misfiring...easy to diagnose if you can interpret the live data.
Thread Starter
3rd Gear
Joined: May 2026
Posts: 3
Likes: 1
Yes, an O2 sensor can cause a misfire whether the sensor is "stuck" rich or lean...the ECM will either over or under fuel the injectors...if you had a Snap On and the misfires were consistent it should have identified what cylinder or cylinders were misfiring...I had a bad O2 years ago "stuck lean" and it was over fueled and the exhaust stunk...3 out of 4 bank 1 cylinders were misfiring...easy to diagnose if you can interpret the live data.
Yeah, it did show what cylinders were misfiring and it was 1,3,5,7 still wasn’t thinking o2 sensor though but it definitely smelt like fuel it was burning my eyes
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From: Cape Coral, Florida
Instructor
Joined: Feb 2016
Posts: 223
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From: St. Marys Ohio
I had the same warning lights and the scan told me it was a miss on #6 cylinder, yep the plug wire was off the coil on 6. Put it back on and the lights went away. The CEL stays on but not flashing. A computer search told me that the light may stay on through a couple of engine cycles. I started it a couple of times in the garage and still on. I took it for a drive for about 5 miles and pulled over and shut the engine off. When I restarted the CEL went off. Being a 2014 with 98k it has time and miles so I think I will replace the plug wires shortly.
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Well, you got rid of the cel & have new plugs , coils, & wires to boot!
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Congrats on the successful repair and thanks for sharing the solution.
Moved to C7 Tech.
Moved to C7 Tech.