A Professional Guide to Brake Fluid Changes by System Type

Traditional Hydraulic Brake System

The traditional hydraulic brake system is a widely used braking system in vehicles such as cars and motorcycles. Its core principle is to use hydraulic force to amplify and transmit the force applied by the driver on the brake pedal to the wheel brakes, thereby achieving the vehicle’s deceleration or stopping. The traditional hydraulic brake system is currently the most mainstream braking solution. It transmits braking force through hydraulic pressure, combined with disc or drum brakes, to achieve efficient deceleration. Despite having certain maintenance requirements, its reliability, cost-effectiveness, and maturity make it the preferred braking system for both passenger cars and commercial vehicles.

The vacuum-assisted hydraulic brake system is the mainstream braking solution for current gasoline vehicles and some hybrid models. It amplifies the driver’s braking force through a brake booster, which is then transmitted via the hydraulic system to apply braking force, enabling efficient deceleration. Thanks to its mature, reliable, and cost-effective design, the vacuum-assisted hydraulic brake system remains the dominant choice for fuel-powered vehicles. However, in the era of new energy vehicles, it is being gradually replaced by electronic braking technologies. The core component of this system, the vacuum booster, plays a crucial role in the braking feel and serves as an exemplary fusion of traditional mechanical and hydraulic systems.

The electronically controlled brake system is a revolutionary upgrade in automotive braking technology. It replaces traditional mechanical and hydraulic force transmission with electronic signals, enabling smarter and more precise braking control. Users are rapidly adopting the system, driving a compound annual growth rate of 23% (data from McKinsey 2024). and is expected to become a standard feature in global passenger cars by 2028. This system not only redefines the boundaries of braking performance but also lays the technological foundation for the era of intelligent mobility.

The electronic parking brake (EPB) is the electronic upgrade of the traditional mechanical handbrake, using electronic control to engage the vehicle’s parking brake and integrate various intelligent features. The penetration rate of EPB in the new car market has already reached 89% (IHS data, 2024), and it is expected to evolve towards full-wire control in the future, becoming a key execution unit in intelligent chassis systems. Its technological evolution directly reflects the development trend of automotive electrification and integration.

Regenerative Braking System (EV/HEV Models)

Brake fluid is the core medium in the brake system, used to transmit pressure and energy during braking. As the brake system evolves from mechanical hydraulics to complex electronic control systems, the process of changing brake fluid has also changed. Factors such as the control structure, level of module involvement, and whether the oil circuit is sealed can all influence the operating methods and tools used. This article primarily introduces two common brake fluid replacement methods.

Because electronic control brake systems lack large brake boosters and vacuum systems, technicians cannot use traditional brake fluid bleeding methods for fluid replacement and bleeding. This makes the equipment requirements more demanding. It is recommended to use the AUTOOL AST series brake fluid bleeder, which can steadily output a fluid replacement pressure of 2-3 bar. This resolves the issue of not being able to establish stable evacuation pressure using foot force alone, making the evacuation process easier and more thorough. A diagnostic device, such as the LAUNCH X431 diagnostic tool, can be used in conjunction with the brake fluid bleeder. This combination can perfectly support ABS/EPB system fluid replacement and is suitable for over 90% of vehicle models.

1. Position the vehicle in the workstation, lift it up, and press the brake pedal to manually release the EFB. Once released, the exclamation mark on the instrument panel indicating the EFB will turn off.
2. Access the vehicle’s infotainment system, go to Settings – Driver Assistance – Brake Service – Release Parking Brake, and select “Yes” without pressing the brake pedal.
3. After performing the above steps, you will hear a long “zzz” sound from the rear parking brake motor, and the dashboard will display a fault light for the EFB system, indicating that the system has been fully disengaged. At this point, you can turn off the engine without further action.

1. Open the brake fluid reservoir cap and use a pneumatic oil extractor to remove the old fluid from the reservoir. Be aware that the reservoir has two layers, making it somewhat difficult to fully drain. Once the old fluid is completely drained, pour the new brake fluid into the reservoir until it’s full.
2. Connect the brake fluid replacement machine to the container of new brake fluid (2-2.5L of new brake fluid) and tighten the cap on the original vehicle reservoir.
3. Replace the brake fluid using the traditional hydraulic brake method.

1. EPB System Reset: Access the EPB function menu and perform the “Install New Brake Pads” or “Exit Maintenance Mode” function. The system will automatically tighten the parking brake calipers. Once successful, the “Service Electronic Parking Brake” warning light on the instrument panel will automatically turn off.
2. Clear Fault Codes (DTC): Return to the main interface, enter the “Read Fault Codes” function, and clear any EPB or ABS error codes generated during the replacement process. Ensure that there are no warning lights on the dashboard.
3. Note: Some electric or hybrid vehicles need to exit “Maintenance Mode” or “High Voltage Disconnection State” before the vehicle can be started.