NHTSA Complaint #11633585 — 2006 TOYOTA PRIUS

The following describes a near total failure of the brake system that accompanies and is triggered by routine aging of the battery. I believe this applies to multiple model years and editions of the Prius, based on reports by other owners on owners' discussion groups. I believe this should have the highest severity level. Here is what happens: An alarm is sounded, several warning lights ABS, VCS appear, and soon after that, the front brakes stop working. The rear brakes then prove ineffective and lock up. The happens with high frequency under any of the following conditions: (a) as the battery approaches 3yrs age, (b) it is excessively cold outside. (c) there is a higher than typical load on the 12V system from any of a variety of reasons. After installing a fresh new 12V battery, the above happens with much less frequency. There no warning on the dashboard to indicate that the condition of the 12V battery is not safe for operation of the vehicle. It seems clear that the route cause is that the brake control unit is configured within inadequate tolerance for the normal aging of the 12V battery, compounded by the absence of warning on the dash. This probably traces back to a poorly chosen LDO voltage regulator in the design of the brake control unit. Recommendation: Review the electrical designs for the brake control unit, all model years, replace as needed and update the dash board computer to provide warning when the battery condition is not sufficient for safe operation of the vehicle. I further recommend that this be done with all due haste, as the condition is quite dangerous. Qualifications: PhD Chemical Physics and Electrical Engineer