Toyota 89411-32020 Sensor, Speed

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The Anti-lock Brake System (ABS) is designed to maintain vehicle steerability, directional stability, and optimum deceleration under severe braking conditions and on most road surfaces by monitoring the rotational speed of each wheel and controlling brake line pressure to prevent wheel lock-up. It works in conjunction with Automatic Skid Control and tire pressure warning systems, where the former helps control skids by braking outside wheels during oversteering, and the latter alerts the driver to low tire pressure through a dashboard light. The actuator assembly includes the master cylinder, an electric hydraulic pump, and four solenoid valves that modulate brake line pressure during ABS operation. Speed sensors located at each wheel generate electrical pulsations to indicate wheel rotational speed, with front sensors mounted to the steering knuckle and rear sensors bolted to the axle carriers. The ABS computer, housed within the actuator, processes information from the wheel speed sensors to control hydraulic line pressure and monitors the system for faults, illuminating an "ABS" light on the dashboard if a problem arises. The built-in self-diagnosis system detects sensor malfunctions and stores failure codes, which can be accessed by turning the ignition key off and using jumper wires on the data link connectors. The ABS warning light indicates diagnostic codes through a series of flashes, with specific patterns corresponding to different malfunctions. After diagnosis, trouble codes can be cleared by jumping terminals on the data link connector and pressing the brake pedal multiple times, after which the system or component should be checked or serviced as needed.