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It's What Makes a Subaru, a Subaru:
Brake Override System –
Avoiding Accelerating Accidentally

 

BOS Overview

 

After BOS activates, it raises the pressure of the brake fluid high enough to stop the vehicle. This is managed by the Anti-lock Braking System (ABS) electronic control unit.

 

BOS also closes the throttle plate to reduce engine speed. At this point, the vehicle cannot accelerate. The accelerator will resume functionality once the driver has fully released it.

 

One of Two Stages

 

How quickly BOS operates is a function of how heavily the driver pushes on the brake pedal.

 

In situations where the brake pedal is lightly pressed along with activation of the accelerator pedal, the system functions with a delay. As a result, the driver still retains control over the accelerator with a brief tap of the brakes.

 

However, if both pedals are hit heavily at the same time, BOS activates immediately. Acceleration yields to braking, and the vehicle stops.

 

Back to Normal

 

BOS deactivates when the driver operates the brake and accelerator pedals separately.

 

The ABS control unit releases brake-fluid pressure. The throttle plate is electronically positioned so the engine runs above idle to prevent it from stalling. BOS also intervenes with engine operation to prevent the vehicle from lunging forward.

 

Finally, BOS synchronizes the position of the accelerator and the operation of the throttle plate so the vehicle drives normally.

 

Enhanced Safety

 

By helping to prevent the driver from accidentally accelerating with the vehicle, BOS contributes to safer driving and greater driving confidence. This Subaru safety system is standard on 2013 BRZ, Impreza, Legacy, XV Crosstrek, Outback, and Tribeca models, and it will be standard on all future Subaru models.

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