http://www.datsc.com/tabid/122/OBD-Error-Code/P0603/Diagnostics/Toyota/Default.aspx
What does this mean?
OBD Code P0603refers to
Battery voltage is supplied to the ECM/PCM even when the ignition switch is turned OFF for the ECM/PCM memory function of the DTC memory, the air-fuel ratio feedback compensation value memory, the idle air volume learning value memory, etc.
Symptoms
Possible sumptoms of OBD code P0603
- Engine Light ON (or Service Engine Soon Warning Light) - Engine may not start
Causes
Possible causes of OBD code P0603
- Loose or poor battery terminal connection - Low battery charge - ECM/PCM power supply circuit is open or shorted - ECM/PCM Programing - Faulty ECM/PCM The Error code is generally activated on detection of the following conditions: Indicates the ECM/PCM has experienced an internal memory fault.
Possible Solutions
- Recharge battery - Resecure and clean battery terminal connection - Reprogram ECM/PCM - Replaced ECM/PCM