Chart A1 - EBCM Problem
WARNING: This page is about a different car, the 1988 Buick Riviera and 1988 Buick Reatta. However, it is still accessible from the selected car via links, so may be relevant.
Codes 11 and 12 indicates problem with EBCM. In most cases, either code indicates replacement of EBCM. Ensure ground circuit is okay. False code can be set due to external electromagnetic disturbances.