Why is your CHECK ENGINE light on?

Why Your Check Engine Light Is On?
This video dives deep into what causes the check engine light to come on, and more importantly, what you SHOULD do about it. We'll break down the most common reasons for the light, from simple fixes like a loose gas cap to potential sensor issues.
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[@pakjohn48]

I discovered another reason for the check engine light. On occasion, while driving with no obvious engine problems nor fault symbols on the dashboard diagnostic display, the car would pass over a pothole in the road causing a mechanical shock to both the car and it's ocupants. Simultaneously the check engine light would illuminate on the dash.and remain on thereafter. If I used my OBD2 reader to turn the check engine light off, it would remain off thereafter until the car ran over another pothole or bump in the road, etc.

[@ArrowGearhead]

Thank you for sharing
It could be an electrical continuity issue due to vibration from the hole, or it could just be a faulty sensor.
Is it only the check engine light or some other light also? What is the code?

[@ThisisTulsa918]

bad fuel, or fuel quality and requirements.

[@shrimp8004]

Why does my check engine light strate flashing when I give it all the gas ,( floor it)

[@ArrowGearhead]

@shrimp8004 would it be a misfire?
What other symptoms do you see?

[@shrimp8004]

@@ArrowGearhead the 2 ground n studs back of 5.3 GMC on passenger side that ground wire is brake n where it's connected to it at an can't remember code but it was knock sensor o ya I do show po300 randem misfire to sorry bout that.