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On February 10, 2005, the Office Of Defects Investigation (ODI) opened a preliminary evaluation to investigate alleged loss of brake power-assist in certain 2004 model year (my) Lexus RX330 vehicles built through approximately June 30, 2004.the subject vehicles were manufactured at Toyota motor manufacturing Canada, Inc.?S cambridge, Ontario assembly plant and were equipped with vacuum brake booster assemblies sourced from aisin seiki co., ltd (aisin) subsidiary advics North America, Inc. (advics-na).to date, ODI is aware of 146 non-duplicative reports that allege loss of brake power-assist and 6 crashes allegedly caused by loss of brake power-assist (resulting in 1 minor injury) on the subject vehicles.the subject vehicles use a conventional brake booster assembly that contains a rubber diaphragm to separate the fore and aft pressure chambers.the outer edge of the rubber diaphragm is held in place via a retaining groove on the brake booster body.if the booster loses vacuum (e.g., operator depletes the vacuum by pressing the brake pedal several times while the engine is off), it may cause the diaphragm to deform in the area of the retaining groove to the point that insufficient seal exists between diaphragm and booster body, thus causing a momentary loss of brake power-assist.the advics-na supplied diaphragm has slightly different material properties compared to the diaphragm inside brake boosters supplied by advics Japan, Corp. (advics-J) and used on 2004my Lexus RX330 vehicles manufactured at Toyota motor kyushu, Inc."S assembly plant.the softer rubber used in the advics-na diaphragm allows greater deformation and is less resilient when compared to the advics-J diaphragm.loss of brake power-assist most often occurs at vehicle start-up and appears to be more prevalent in colder temperatures.most owners report that brake system operation returns to normal within a few seconds after vehicle start-up.testing conducted by the manufacturer indicates that the advics-na diaphragm?S reduced ability to return to shape is exacerbated by colder temperatures and that loss of brake power-assist at start-up may last for a maximum of 95 seconds at temperatures below "20 degrees celsius.however, the subject vehicles have a back-up system that can sense a loss of brake power-assist and enable the ABS actuator for brake hydraulic pressure support (I.e., brake pedal force assist).the manufacturer will conduct a service campaign (Lexus special service campaign #5la) to replace the vacuum brake booster assembly on all affected subject vehicles.the action taken by the manufacturer is sufficient to resolve the issues raised by this investigation.accordingly, this investigation is closed.the closing of this investigation does not constitute a finding by NHTSA that a safety-related defect does not exist.the Agency will take further action if warranted by the circumstances.
