It's most likely not catastrophic. Do as Matt suggests and connect into the ODB2 with a code scanner. You need to buy one anyway if you work on '96 and newer cars. This should allow you to clear the codes.

In the future, no matter what you are working on always take the time to properly charge the battery by connecting directly to the battery posts making sure the cables from the car are already removed completely.

Good Luck,

-GH

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1992 Mercedes Benz 500SL
1998 BMW 528i
2003 Honda Element
2002 CBR600F4i
1977 Coachmen Motor Home