DTC P0603 - Powertrain Control Module (Pcm) Memory Reset: Condition
WARNING: This page is about a different car, the 1996 Pontiac Firefly and 1996 Geo Metro. However, it is still accessible from the selected car via links, so may be relevant.
PCM has detected a failure in communication circuitry. Replace PCM if DTC P0603 is set. DTC P0603 will set when an EEPROM data readout occurs.