Disconnect Battery
WARNING: This page is about a different car, the 2003 Pontiac Grand Prix, 2003 Chevrolet Malibu, and 2003 Buick Century. However, it is still accessible from the selected car via links, so may be relevant.
NOTE:
On many OBD-II systems, PCM will retain memory for an extended period of time with battery disconnected. Memory may be retained for several days.
Disconnecting PCM power or battery ground will clear all PCM memory including DTCs, freeze frame, failure records, adaptive learning and system monitors.