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 performs many diagnostic tests to verify proper operation of internal ECU systems. One of these tests checks for errors after a memory read/write diagnostic test.
If the HV control ECU detects this malfunction inside of the ECU, it will illuminate the MIL and set a DTC.