When CEL flashes it usally is detecting a engine missfire. When the CEL flashes it also means you should have checked ASAP due to the fact that continued driving with an missfire can be damageing to the catalytic converts.
[v. mis-fiuhr; n. mis-fahyuhr] Show IPA verb, mis·fired, mis·fir·ing, noun
verb (used without object)
(of a rifle or gun or of a bullet or shell) to fail to fire or explode.
(of an internal-combustion engine) to fail to ignite properly or when expected.
to fail to achieve the desired result, effect, etc.: His criticisms completely misfired.