Circuit Description
WARNING: This page is about a different car, the 2004 Lexus SC 430. However, it is still accessible from the selected car via links, so may be relevant.
The telephone ECU monitors the portable phone-L battery (backup battery) voltage at terminal SUB BATT. When the voltage drops, this DTC is output. If the battery is normal and recharged with the ignition switch ON, the DTC will be cleared.