FWIW --- debugging my son's 1993 Firebird I ran into these simple steps to clear SES (Service engine Light) in this mid-year model.

1. pull both fuses for the ECM (EFI) computer and battery in the fuse box to the left of the drivers side light switch in the door jam.

2. step on the brake for 1 minute.

3. replace fuses

Codes are clear now. verified no codes stored after using this procedure with a CanOBD1 tool kit (which reads but can not reset SES codes ).