check engine light

my girlfriend has an 07 caliber, 2.0, 66,000 miles. She was losing power when the ac was on, I disconnected the battery and replaced the plugs with NGK's, now it runs fine but has check engine light which wasn't there before. Any ideas?? Thanks

you can dissconect the negative battery cable for 5 minutes , it should clear any codes , if it comes back on ,you may have knocked a wire loose somewhere when you did the plugs.

the check engine light has cleared itself . thanks for the replys