Check engine light comes on then flashes

Engine misfire ! Flashing check engine light , catayltic converter damaging misfire . Been on for three years ? No inspection were you live ? Flashing check engine light CarMD

A blinking or flashing check engine light indicate misfiring. I suggest you check the components of your secondary ignition system especially if it worsens when it's damp.

Change coils,fuel filter and check the code.

The check engine light is because all check engine light codes are caused by components that affect emissions. It's not actually an engine problem, it's a problem with either your O2 sensor, MAF sensor, fuel/air ratio, pyrometer, or exhaust.
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gm diagnostic tools

If it is running rough & no check engine light on then the first thing I would to is tune it up. If you have a check engine light then pay someone to diagnosis it & go from there. Usually when the light comes on there is a more promenient issue; that is WHY the light continues to flash.

the light is flashing from a misfire have it scanned and the codes will lead you to the bad cylinder

Its either running too rich or too lean, either way have it seen to quickly or engine damage MAY result.

Go to Advance or Auto Zone and have them run an obd scan on it and it will pin point why your light is on and could solve your problem. This is often done for free.

WHEN THE LIGHT IS FLASHING IT MEANS THAT YOU HAVE A MISFIRE. I SUGGEST YOU REPLACE PLUGS AND WIRES. BECAREFUL DRIVING BECAUSE ALTHOUGH UNLIKLY, IT COULD BE MORE SERIOUS AND CAUSE A FIRE