Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
Principles of Operation: Brake-By-Wire
During a normal brake application, the brake pedal feel simulator allows the pressure applied to the brake pedal by the driver's foot to act against a spring instead of the brake booster push rod. The brake pedal angle sensor is mounted to the brake pedal assembly and provides the ABS module with an analog signal indicating the amount of deceleration the driver is demanding. If it is necessary for the conventional friction brakes to be applied, the ABS module applies a Pulse Width Modulated (PWM) voltage to a vacuum solenoid inside the active brake booster. The solenoid allows vacuum from either the combustion engine (if the engine is running) or the electric vacuum pump to move the booster push rod which in turn pushes the piston in the master cylinder and create hydraulic brake pressure. If the brake pedal is applied quickly and forcefully enough, the driver can overcome the brake pedal feel simulator spring pressure, allowing a direct connection between the brake pedal, booster push rod and master cylinder.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.