TSB: Some 2021 model year Sienna Hybrid vehicles may exhibit a depleted 12V auxiliary battery when in IG-OFF due to a condition in which the Hybrid Vehicle Electronic Control Unit (HV ECU) does not sleep. The HV ECU may not sleep if any of the following have occurred with the vehicle:
? The vehicle was towed or jump-started after a 12V battery discharge.
? The vehicle?s 12V battery was disconnected and reconnected, as when accessories were installed.
? The 12V battery terminal(s) or power or ground harnesses were removed to repair the vehicle.
? A new 12V battery was put into the vehicle, or there was an open in the main fusible link.
? Any other condition that may have caused power not properly flowing from the 12V battery through the harness.
The HV ECU logic has been updated to reduce the possibility of this condition. Follow the Repair Procedure in this bulletin to address this condition.
