I just changed spark plugs in a o8 hhr and the engine light came on it starts no problem and runs great I don't understand what could be the problem
spark plugs on 2008 Chevrolet HHR
You could reset the Check Engine light with a scan tool or just disconnect the battery. You may have had the ignition key on when you disconnected the ignition coil. Better yet if there is no fault the computer does a self check and after a few drive cycles will turn the light off itself when it realizes the fault is gone.