2001 Honda Accord EX 2.3L 4cyl. check engine light is flashing off and on with a PO1399 code
That code indicates random/multiple misfires. And if the Check Engine light is flashing it means the misfires are serious enough to where damage to catalytic converter can occur.
I wouldn’t drive the vehicle until it’s found out what’s causing the code. Unless you don’t mind spending the money on a replacement catalytic converter.
I wholeheartedly agree with Tester.
Unfortunately, there are numerous possible causes for this condition. You’d be better to just have it towed to a good reputable shop and let them diagnose it hands-on.