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2004 CTS 3.6L check engine light flashes

My 2004 Cadillac CTS 3.6L started running rough, check engine light flashed on and off. Codes P0300 and P0303. Car has about 119000 miles. Could this be just be the plugs? Car has been running fine up to today.
Thanks for any help you can offer.

Those are misfire codes so sure: it could be the plugs or wires and anything related to spark.
Have those parts been replaced in the car’s lifetime? If not, it may be due.

When the Check Engine light flashes it means the engine has a major misfire. And driving the vehicle with the Check Engine light flashing can result in damage to the catalytic converter(s).

It could be plugs or anything else to do with the ignition system or even the engine. Drive it to the nearest service center and have them figure out what’s causing the major misfire.