Toyota 83181-12020 Vehicle Speed Sensor

The anti-lock brake system, introduced in 1988, is designed to maintain vehicle steerability, directional stability, and optimum deceleration under severe braking conditions and on various road surfaces by monitoring the rotational speed of each wheel and controlling brake line pressure to prevent wheel lock-up. The actuator assembly includes the master cylinder, an electric hydraulic pump, and four solenoid valves, with the pump providing hydraulic pressure to charge the reservoirs that supply pressure to the braking system. Speed sensors located at each wheel generate electrical pulsations to indicate wheel rotational speed, with front sensors mounted to the brake backing plates on 1988 and 1989 models, while later models have sensor rings integrated with the outer Constant Velocity joint. Rear wheel sensors are bolted to the brake backing plates or axle carriers, with sensor rings integral to the rear hub assemblies. The ABS computer, mounted under the dashboard for earlier models and in the luggage compartment for later ones, processes information from the wheel speed sensors to control hydraulic line pressure and prevent wheel lock-up, while also monitoring the system for faults. If a problem arises, an "ANTI-LOCK" or "ABS" light will illuminate on the dashboard, and a diagnostic code will be stored for retrieval by a service technician. If the dashboard warning light remains on during operation, the ABS system needs attention, and while a special electronic ABS diagnostic tester is required for proper diagnosis, preliminary checks such as verifying brake fluid level, ensuring electrical connectors are secure, and checking fuses can be performed by a home mechanic before seeking professional repair.