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How To Bleed ABS Brakes and Symptoms of Bad ABS System

Bleed ABS Brakes

Modern cars come with an anti-lock braking system (ABS) that uses brake fluid and a pressure system to operate. Over time, moisture or air bubbles get into the fluid which is bad for the braking system. When this happens your pedal will feel spongy and it’s usually difficult to feel exactly when the brakes begin to bite. Not even new brake pads can solve this problem. Ideally, fresh, thick brake pads should bring the pedal back up but if air is in the braking system it would not. When this occurs, it would be helpful if you know how to bleed ABS brakes. 

Auto Repairs Are EXPENSIVE

What happens when air gets into your ABS system?

The air can get into the braking system in different ways but all of them have one thing in common and that is it involves brake fluid. Your brakes are a hydraulic system meaning fluid makes them function. Hitting the brake pedal pushes brake fluid out to the brakes at the 4 corners of the car. What moves the brake pads inward to clamp down on the rotor and slow the vehicle using that friction is the fluid pushing into the brake caliper in a disc brake. Older types of drum brakes function using the same principle, even though the braking compound chunks wear down in drum brakes are in shoes, rather than pads. Push the brake pedal down and the brake fluid shoves the shoes outward against the metal drum, hence also making use of friction to slow the vehicle. Plenty of vehicles still utilize drum brakes in the rear because the front brakes do most of the job. (To make it simpler, we’ll call bothe shoes and pads as a “pad” since both have the wear material that makes the brakes stop)


Over time, pads wear down and need more fluid to push them onto the braking surface. When the brake pads wear so thin that the fluid level plummets too low in the master cylinder reservoir, some air bubbles may get into the brake lines. Air is a lot easier to compress than liquid thus bubbles in the brake lines behave like a very soft spring in that solid column of fluid between the foot and brake drums or calipers. You’ll need to know how to bleed ABS brakes to flush the air out. When bleeding out the air bubbles, it is highly recommended to flush all of the old fluid out of the system and replace it with a new fluid. Atmospheric dirt and abrasive metal wear particles from moving components in the brake calipers and cylinders contaminate the brake fluid over time. 


Moreover, brake fluid absorbs air moisture which decreases the boiling point enough to make it boil at the end of a long downhill grade or some other instances like a track day where the brakes are being used again and again or for a long time. Imagine a pot on the stove where boiling fluid creates springy air bubbles. Hot temperatures also deteriorate the alcohol-based fluid itself. In time, brake fluid that was somewhat clear when it went in may begin to appear more like coffee.

Antilock braking systems tolerate contaminated fluid and air less than systems without ABS. TheABS hydraulic pump runs at plenty of thousand psi, which forces brake fluid through very tiny valves. It can whip brake and air fluid into a foam resembling a latte foam making bleeding air out of the system even harder. To make it worse, those small abrasive particles can easily be damaged by the valves and ABS pump. Good thing, air that gets into the ABS controller can bleed out. But some cars need the use of a special ABS scan tool to cycle the valves and pump to remove all the air inside. You can prevent these ABS problems from happening by regularly remembering to bleed and flush the brake fluid which you can even do at home. 

What is the correct order to bleed brakes?


This is the correct order to bleed the brakes: 


First, begin by getting about 16 ounces of fresh brake fluid. An unopened can, as expected, has a longer shelf life compared to an opened can that must be thrown away within a few weeks. Put the car up on jackstands, taking off all four wheels.


Second, be sure to loosen the bleeder valves. A box wrench that can fit the bleeder bolt is needed. It will serve as a vise-grip or a crescent wrench to strip off the bolt’s edges and make loosening it impossible. A spritz of penetrating oil on the bolt may help before bleeding the brakes especially if rust is typical where you live. Loosen these bolts, but for now keep them closed. If nothing is happening even after using some penetrating oil, what you can do is tap the wrench very lightly with a tiny hammer. If the bleeder valves cannot be turned off without breaking them off, a replacement of the brake calipers or wheel cylinders might be needed. You should be careful handling them as they are tiny, hollow bolts. 


Next, with a kitchen tool like a small turkey baster, take off the top of the master cylinder reservoir and purge out as much of the old brake fluid as you can. Using a clean and lint free cloth clean any particles or sediments out of the now empty reservoir. Brake fluid is caustic and will damage the paint and finishes on your vehicle so keep in mind not to allow it drip on your bodywork or wheels. Put some extra shop towels around on your work area just in case, and wipe off any fluid dripped onto a painted surface right away. 


Now that the reservoir is clean, attain a piece of clear plastic tubing that fits perfectly over the end of the bleeder bolt. Aquarium tubing is ideal for this, and it’s affordable. Press one end of the brake bleeder bolt at whichever corner is farthest from the reservoir. Place the other end of the tube into a small, clear bottle with an inch or two of clean brake fluid in it to prevent the air from being sucked back into the brake cylinder or caliper. 


Place a piece of 1 by 4 lumber or some other spacer beneath the pedal to keep it from traveling too far and overextending the brake master cylinder when the line pressure is released and the brake system is released.


Put new fluid on the empty master cylinder reservoir with fresh fluid up to its maximum fill line and put the cover back on the reservoir. Fluid can go out of an open reservoir each time the pedal is released. 


Have Someone To Assist You


The person who will help you should know how to follow instructions to a T. Your assistant will sit in the driver’s seat and wait for your orders. 


When you say down, your assistant will depress the brake pedal all the way down with about the same amount of force required to prevent the vehicle from rolling forward at a traffic light. The helper will say down to let you know but continue to press the pedal. Notify your assistant that the brake pedal is about to lose pressure and sink to the stop you’ve placed behind it on the floor, but nonetheless the person must continue to press it. Crack the bleeder bolt a quarter-turn. 


Some of the old fluid will ooze down the tubing into the bottle and you’ll likely notice a few clear bubbles in the line. Once the flow stops, shut the bleeder. Tell the helper “Up.” The person will then say “Up” to confirm, and take off their foot from the pedal. Repeat the process until you can see fresh, clear fluid comes from the bleeder screw without bubbles in it. Any out of order moves here can suck air into the caliper. Even if the end of the tubing is immersed in fluid, air can still go through the bleeder bolt threads into the caliper if there is negative pressure in the system while the bleeder screw is split open.


Put fresh fluid on the brake fluid in the reservoir every six or so pumps. Make sure that the reservoir does not get more than half empty because air can be sucked into the master cylinder if the fluid level goes too near the reservoir’s bottom. Most reservoirs come with a “Minimum” line so make sure that the brake fluid level never goes below that line.


When clean fluid is coming through the tubing, secure or tighten the bleeder bolt and move the operation to the left rear brake. There, repeat the same routine with your assistant until clean fluid without any bubbles ooze out of the tube. Do the same process with the right front brake and finally with the left front brake. The plan is to work from the calipers farthest away from the brake fluid reservoir inwards to purge the contaminated fluid in the farthest reaches of the system out first. It might be best to double check what you have done by going back around to each caliper in the sequence you flushed them, reconnecting the tube and giving the system a few pumps to make sure that a solid stream of clean fluid comes out. Once done with each corner, close the bleeder screw and be sure to top off the brake fluid reservoir as you go. 


Lastly, fill the brake fluid reservoir to its MAX level line, put the wheels back on the vehicle and go for a drive to be sure that solved the problem. 


Note: Check your car’s service manual to know the right way to bleed your car’s ABS since there might be a bleeder bolt right on the ABS controller or you may need to borrow or get an ABS-capable scan tool.

How do I know if my ABS module is bad?

When the ABS is not working, there’s a significant chance that a loss of traction, skidding and hydroplaning will occur under heavy braking conditions. Knowing what signs to look out for when an ABS system goes bad is important so you can address the issue as soon as possible. Here are common signs of a failing ABS module:


The ABS Light is on


The most common indication of an ABS system issue is the ABS Light illuminating. It will show an amber color, and indicates that there is a problem with the ABS system. Older cars that come with older versions of ABS systems may use a Check Engine Light instead of an ABS Light.


Brake pedal is not responding


In certain conditions, depending on the car model, when the ABS module goes bad, the brake pedal may not respond. This is an issue you cannot miss since having an unresponsive brake pedal will not stop a car, or will not be able to function in a safe manner. Most of the time, it happens slowly and over time. Typically, the brake pedal will become increasingly difficult to press until it becomes unresponsive. 


Brake pad takes more effort to push


When all braking system parts are working as it should be, the pedal should need very little effort to press down. Once pressed, it should have an immediately recognizable effect in slowing down the car. If you start to notice that the pedal is taking more effort for it to get the same amount of braking force, your ABS module might have an issue. 


The brakes are locking up


When the ABS system is working as it should be, it prevents the wheels from locking up during heavy braking to prevent loss of traction. But there are times where a bad ABS module can act erratically which causes brakes to lock up even under normal driving conditions. If your brakes are behaving sporadically like random clicking sounds, and/or pumping of the brakes, then the ABS module may need replacement.



The brake system is vital in making sure you are driving safely. When air gets into the brake fluid, it is a must to bleed ABS brakes immediately. You can do it on your own with the help of an assistant. But if you don’t mind the cost to have your brakes bled, you can also get it done by a mechanic. Also take note of the warning signs of a bad ABS module so you can prevent bigger and more expensive repairs.


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