DTC P0603: Keep Alive Memory Error
WARNING: This page is about a different car, the 1997 Suzuki X-90. However, it is still accessible from the selected car via links, so may be relevant.
Turn ignition off. Connect scan tool to Data Link Connector (DLC). Turn ignition on. Clear DTC(s). Start engine and run for one minute. If DTC(s) reset, replace PCM and retest system. If DTC(s) do not reset, check for an intermittent problem. See TESTS W/O CODES article.