This happens all the time.
The engine light is on and starts blinking when I go over 35mph. on 2004 Cadillac CTS
DON"T drive the car with the MIL blinking! The blinking means IT IS doing damage to the emissions system (kind way of saying you're trashing your catalytic converter(s) and likely worsening whatever the cause of the problem is.Have it scanned for codes .
To further assist, an mil code is needed. You might be able to get this code scanned for free at a local auto parts store.