Monitor Description
WARNING: This page is about a different car, the 2004 Toyota Prius. However, it is still accessible from the selected car via links, so may be relevant.
The HV control ECU monitors an ST signal input from the power source control ECU. If the ST signal is shorted to the +B power supply, the HV control ECU interprets this as the ST signal error, and then illuminates the MIL and sets a DTC.