How does the ABS sensor in a car work?

[Debbie]

ABS system, also known as the Anti-lock Braking System, works as follows: During braking, the ABS closes the normally open input solenoid valve on the wheel that begins to lock based on speed signals from each wheel speed sensor, keeping the braking force constant. If the wheel continues to lock, the normally closed output solenoid valve is opened. This ensures the braking state remains at the optimal point, achieving the best braking effect and maximum driving safety. ABS, short for Anti-lock Braking System, functions by automatically controlling the braking force during vehicle braking to prevent wheel lock-up. It maintains the wheels in a state of rolling and sliding (with a slip ratio of around 20%), ensuring maximum traction between the wheels and the road. The ABS system primarily consists of four components: wheel speed sensors, the electronic control unit (ECU), the hydraulic unit, and the ABS warning light. The wheel speed sensors detect the motion state of the wheels and generate sinusoidal electronic pulse signals. These signals are then processed by a modulator, converted into digital signals, and transmitted to the electronic control unit. The central electronic control unit (ECU) receives input signals from the wheel speed sensors and uses them to calculate the wheel speed, vehicle speed, and slip ratio. Based on the slip ratio, it determines the wheel's condition and issues control commands to the hydraulic unit. The hydraulic unit adjusts the pressure in the brake lines according to the control commands, with the adjustment process including pressure maintenance, pressure increase, and pressure reduction. The ABS warning light alerts the driver to any system malfunctions. If the ABS warning light illuminates, it is advisable not to continue driving. An illuminated ABS light indicates a malfunction in the vehicle's anti-lock braking system. During emergency braking, if the wheels lock up, the vehicle may skid uncontrollably, preventing the driver from slowing down or adjusting the vehicle's trajectory, posing significant safety risks.

[GrantFitz]

When I first learned about how ABS sensors work, it was actually quite straightforward. That little gadget is mounted near the wheel, containing a small magnet and coil assembly, with a toothed metal ring (like a tiny comb) on the hub. As the wheel rotates, the teeth pass by the sensor, creating electrical pulse signals through magnetic field changes. These signals are sent to the car's brain—the ABS control unit—telling it how fast the wheel is spinning. If you slam on the brakes and the wheel speed drops too abruptly, nearing lock-up, the system instantly adjusts brake pressure via a hydraulic pump, pulsing the brakes on and off to prevent skidding. This lets you maintain steering control and avoid accidents. Though inconspicuous, it’s a lifesaver—I often remind friends to keep their wheels clean, as mud buildup can interfere with sensing. The whole process happens in milliseconds, with a clever, space-saving design.

[DelWeston]

Over decades of driving, the ABS sensor has saved me countless times. It works silently, with one placed near each wheel to monitor whether the rotation speed is uniform. The sensor detects the toothed ring on the wheel, sending an electrical signal to the computer control unit each time it passes. If it detects a wheel slowing down significantly and nearing lock-up, the computer instantly fine-tunes the braking force to prevent skidding. This gives me a slight buzzing sensation underfoot during hard braking on snowy roads, while the wheels remain under control, allowing the car to stop steadily. Its benefits go beyond preventing skidding—it also reduces the risk of rear-end collisions. However, if the sensor gets dirty, inaccurate signals can affect its performance, so it’s recommended to check the wheels regularly and not overlook safety details. Simply put, it’s a silent guardian, ensuring peace of mind on every trip.

[DeNora]

ABS sensor issues are common, such as being covered by mud or failing due to wear. It operates on the principle of magnetic induction, where the toothed ring passing the sensor during wheel rotation generates pulse signals to measure speed. These signals are sent to the control unit for analysis. If a rapid decrease in wheel speed is detected, the unit sends commands for pulsed braking to prevent wheel lock-up. If the sensor is dirty, it may send false signals, causing the warning light to illuminate and the system to fail, requiring cleaning or replacement. Don't underestimate its importance—it can be a lifesaver in critical moments.