Circuit Description - DTC P3109 - Information Codes 218, 219, 220, 221: Notes

WARNING: This page is about a different car, the 2002 Toyota Prius. However, it is still accessible from the selected car via links, so may be relevant.

NOTE:

When using an OBD II scan tool other than TOYOTA hand-held tester, check all the steps.
When using TOYOTA hand-held tester, confirm the information code and check it.

The HV ECU performs multiple checks to avoid any malfunction that may occur through the communication with the brake ECU due to a noise, etc.