Key Reminder System
WARNING: This page is about a different car, the 2003 Lexus RX 300 and 2002 Lexus RX 300. However, it is still accessible from the selected car via links, so may be relevant.
If the driver door is opened with the ignition switch set at the ACC or OFF position and the ignition key remained inserted into the key cylinder (the unlock warning switch is on), the signal from the unlock warning switch is input to terminal KSW of the body ECU and the signal from the front LH door courtesy switch is input to terminal CTY of driver door ECU. See WIRING DIAGRAMS . As a result, through communication control of the body ECU and door ECU etc. the buzzer in the combination meter goes on to warn the driver that the ignition key is still inserted.