How to manually bleed the ABS pump?
2 Answers
ABS pump manual bleeding method: After bleeding once, perform emergency braking 1 to 2 times and then bleed again. This will gradually carry the air in the new master cylinder into the pipelines and remove it during the next bleeding. Repeated bleeding will eventually remove all the air. The bleeding sequence is: right rear wheel, left front wheel, left rear wheel, right front wheel. How ABS works: During braking, the ABS quickly determines the wheel lock-up state based on the speed signals from each wheel speed sensor, closes the normally open input solenoid valve for the wheel that is starting to lock, and keeps the braking force unchanged. If the wheel continues to lock, the normally closed output solenoid valve is opened, and the braking pressure on that wheel rapidly decreases due to the direct connection to the brake fluid reservoir, preventing the wheel from completely locking due to excessive braking force. This keeps the braking state always at the optimal point (slip ratio S of 20%), achieving the best braking effect and the safest driving.
I've got some experience dealing with ABS pump bleeding, having worked on cars myself for years. The whole process isn't difficult, but needs to be done step by step. First, make sure the vehicle is securely parked, preferably on level ground with the handbrake engaged—safety first. Locate the ABS pump unit's bleeder screw—its position varies by model, usually somewhere toward the front of the chassis, so checking the owner's manual is more reliable. Prepare a clear hose and a small container, then attach it to the bleeder screw. Get a friend to help pump the brake pedal a few times to maintain pressure. Slowly loosen the screw, and you'll see brake fluid with bubbles flowing out; keep pumping until the fluid runs clear and bubble-free. Don't rush—repeat this two or three times to ensure it's clean. Once done, tighten the screw and top up the brake fluid to the standard level. I usually use DOT 4-grade fluid to prevent system corrosion. Remember, brake fluid is toxic, so wear gloves to protect yourself and the paintwork. After manual bleeding, the brakes will feel extra responsive—I recommend regular maintenance to avoid safety risks.
