Antilock brake system (ABS) is equipped on vehicles as a standard item. An overview of ABS construction and operation will help you understand the troubleshooting method when you study it.
Antilock Brake System Introduction
The antilock brake system (ABS) prevents a vehicle’s wheels from locking when the brakes are applied, thereby maintaining steerability.
Locking of a vehicle’s front or rear wheels is extremely dangerous. If the front wheels lock (for example, during hard braking or when the brakes are used on a slippery road surface), the driver loses directional control and the vehicle continues moving in its current direction. If the rear wheels lock, the vehicle can spin around. An ABS controls the brakes in such a way that the wheels do not lock.
Even an inexperienced driver can therefore brake safely and effectively. In an emergency, ABS enables the driver to apply the brakes while steering around an obstacle.
The maximum braking force is limited by the performance characteristics of the brakes. ABS does not enhance the brakes’ performance characteristics and achieve shorter stopping distances. It simply ensures that the brakes operate with maximum efficiency.
On gravel and deep, fresh snow, shorter stopping distances can, in some cases, be achieved with the wheels locked.
During ABS operation, variations in brake hydraulic pressure create slight kickback at the brake pedal. It is possible to make systems that operate without kickback. However, current systems are intentionally designed to create kickback since it provides an indication of ABS operation.
In the event of ABS malfunction, ABS warning lamp illuminates. In such condition, the brakes remain useable but the anti-lock function is lost.
Antilock Brake System Components and Function
Then the control unit causes the modulator to reapply the brake by increasing the fluid pressure. Thus, the wheel speed drops again to a level at which locking can occur. By repeating this operation very rapidly, the ABS keeps the wheel close to a lockup condition.
Types of Antilock Brake System
Systems used in current Honda vehicles can be divided broadly into two types: Honda developed ABS (developed by Honda) and OEM ABS (developed by a third-party auto parts manufacturer and used from 1996 Civic). In terms of construction, the biggest difference between a Honda-developed ABS and an OEM ABS is that the hydraulic control and regular braking circuits are independent of each other with a Honda-developed ABS.
In a Honda-developed ABS, pistons in the modulator are actuated by hydraulic pressure, thereby altering the size of chambers that is connected in series with the brake hydraulic lines. As a result, the brake hydraulic pressure is controlled as required.
In an OEM ABS, the brake hydraulic pressure is controlled directly using solenoid valves and a pump.
Precautions for Antilock Brake System Service
Honda-developed ABS has two types of circuits – high-pressure circuit and low-pressure circuit. When replacing the ABS brake fluid, operation for the low-pressure circuit is the same as that for the conventional brake system. For the high-pressure circuit, however, a special procedure is required. For OEM ABS, brake fluid replacement procedure is the same as that for the conventional brake system.
- Accumulator
- Outlet solenoid valve
- Inlet solenoid valve
- Motor
- Piston/valve
- Pump
- Pressure switch