July 1: So it begins. Don't worry, this is not in the correct legal jurisdiction!
Diagnostic Aid
WARNING: This page is about a different car, the 1990 Chevrolet Corvette. However, it is still accessible from the selected car via links, so may be relevant.
Problem may be intermittent. Try performing tests shown while wiggling wiring and connectors; this can often cause fault to appear.
Fig 1: Code 72, Elect Brake Control Mod ECBM Serial Data Line Fault