How to Bleed Your ABS Brake System

Brakes, Tires and Wheels

By Rodney (Mechanics)

Whenever you mess with your car’s brake system—like swapping out parts such as calipers, the master cylinder, or brake lines—air gets in. And if you want your brake pedal to feel nice and firm, you gotta get rid of that air. Air bubbles in the lines or parts like calipers or wheel cylinders will make your pedal feel all soft and mushy.

Here’s the deal: when you hit the brakes, those air bubbles need to get squished before the hydraulic fluid can do its job and stop your car. Now, if your vehicle has anti-lock brakes, you can usually bleed the brakes like normal, unless air sneaked into the ABS modulator assembly. If the only parts you swapped were downstream of the modulator, no worries—standard bleeding should do the trick.

When it comes to bleeding brakes, you’ve got options: manual bleeding, power bleeder, injector tool, or vacuum bleeder. Doesn’t matter which method you pick, as long as you flush out all the lines and parts to get rid of any air.

How to Bleed Your ABS Brake System

Typically, you start by bleeding the brake farthest from the master cylinder, then move on to the one that shares the same hydraulic circuit. After those are done, you tackle the other brake circuit, starting with the farthest one from the master cylinder.

Always check the manufacturer’s bleeding sequence—they might have their own way of doing things.

But let’s say you replaced the master cylinder or some parts before the ABS modulator. Now, that’s a bit trickier.

Getting air out of an ABS modulator can be a headache because of all the nooks and crannies inside. Some have special bleed screws to help, while others need a scan tool to cycle the ABS solenoids during bleeding.

ABS Modulator Bleed

To understand what you’re up against, let’s dive into some bleeding procedures for common General Motors ABS systems.

Unlocking Brake Performance: Step-by-Step DELCO ABS-VI Bleeding Procedure

Back in 1991, General Motors introduced the Delco ABS-VI anti-lock brake system as an option on some of their cars like Saturn, Buick Skylark, Oldsmobile Cutlass Calais, and Pontiac Grand Am. Since then, it’s been used on a bunch of GM front-wheel-drive vehicles like Chevrolet Lumina, Beretta, and Cavalier, Pontiac Grand Prix and Sunbird, and others.

This Delco VI system is a type of ABS that doesn’t mix with the brake cylinder and power booster. It’s got sensors on all four wheels but works on three channels. Basically, it handles the front brakes separately while the back ones share a circuit. The hydraulic modulator and motor pack sit next to the master cylinder, and when disconnecting them, you gotta replace certain tubes and O-rings to avoid leaks that could mess up your brakes.

Inside the modulator assembly, there’s a lot going on—fluid chambers for each brake, solenoid valves, motors, and gears. Good news is, if something goes wrong, you can replace parts like the motor pack or solenoid valves without swapping out the whole thing.

When it comes to bleeding the brakes on cars with Delco ABS-VI, you’ve got options: manual, vacuum, or pressure bleeding. Usually, you start with the right rear, then the left rear, followed by the right front, and finish up with the left front.

But before you dive in, you’ve gotta make sure those rear pistons in the modulator are in the right spot. If not, bleeding the rear brake lines won’t work. You can use a scan tool to get them where they need to be, or if you don’t have one, there’s a manual trick involving the front bleeder screw.

Once everything’s set, bleed the brakes, and after making sure the pedal feels solid, take the car for a spin. The system will reset itself, and then you can bleed the rear brakes.

DELPHI DBC-7 ABS Braking System

Back in 1999, General Motors rolled out the Delphi DBC-7 ABS Antilock Brake System on cars like the Buick Regal and Century, and the Chevrolet Tracker. It was the follow-up to the older Delco ABS-VI system. By 2000, it took over on more GM models like the Monte Carlo, Chevrolet Impala, Malibu, Venture, and Cavalier, along with others like the Pontiac Sunfire and Montana, and the Oldsmobile Cutlass and Silhouette.

Now, unlike its predecessor, the ABS-VI system, the DBC-7 doesn’t use motor-driven plungers. Instead, it relies on solenoids, like most other ABS setups. The Brake Pressure Modulator Valve (BPMV) is where the action happens, with separate valves for applying and releasing pressure to each brake, along with accumulators for each brake circuit. This means you’ve got a total of six, eight, or ten ABS valves, depending on the setup of your car’s ABS system.

For GM passenger cars, they’ve got the four-channel ABS deal going on, meaning each BPMV outlet is hooked up to a brake line for a different wheel. And for easy identification, they’ve color-coded the lines: purple for left rear, yellow for right rear, red for left front, and green for right front.

ABS Sercive Bleed

Unlocking the Secrets of DBC-7 Bleeding Procedures

When it comes to bleeding brake lines, you can stick to the usual method as long as no air has snuck into the ABS modulator. But if there’s air in there, you’ll need a pressure bleeder and a scan tool:

  1. Hook up the pressure bleeder to the master cylinder reservoir.
  2. Turn on the ignition.
  3. Close the bleeder screws and pump up the pressure to 35 psi.
  4. Use the scan tool to select the Automatic Bleed Procedure. It’ll get those ABS solenoids in the BPMV buzzing for a minute.Next, the scan tool will tell you to bleed each wheel. While you do this, the pump will run and the release valve will do its thing for one minute at each wheel. Then, there’s a final 20-second round of solenoid cycling to make sure any leftover air gets kicked out.
  5. Release the pressure from the bleed tool and take it off the master cylinder. Then, check the pedal to make sure it’s nice and firm with no air bubbles left.

Bosch 5 ABS Systems

Back in 1995, Corvettes got a new ABS system from Bosch, known as the Bosch 5 ABS. It took over from the older Bosch ABS/ASR system. This Bosch 5 system also found its way into other cars like Cadillac Deville, Buick Estate Wagon and Roadmaster, the 1996 to 1999 Chevy Caprice and Impala, and  Seville, Fleetwood, and Eldorado.

Now, with this Bosch 5 setup, each brake circuit gets its own solenoid in the modulator assembly. But here’s the good news: you don’t need any fancy bleeder valves or special scan tool procedures. You can bleed the brakes the old-fashioned way. Just go in the usual sequence: right rear, left rear, right front, and left front.

Techniques for Bleeding Older Integral ABS Systems

Integral ABS systems are no longer in use, but you might still come across them in older vehicles. For instance, GM vehicles like the 1989-91 Buick Regal, Oldsmobile Cutlass, and Pontiac Grand Prix and GTU models used the Delco III Powermaster system, which works similarly to other integral ABS systems like the Teves Mark 2, Bosch III, Bendix 9, and Bendix 10.

Integral ABS systems rely on a high-pressure pump and accumulator for both assisted braking and anti-lock braking. Ahead of getting into any brake repairs, it’s important to depressurize the accumulator at first. These systems sometimes can reach pressures as high as 2,700 psi, so beware before engaging with brake lines or ABS hydraulic components. This can be done by firmly pumping the brake pedal 40 times and turning off the ignition.

Once repairs are done, you can bleed the lines using different methods like manual bleeding, power bleeding, injector tools, or vacuum bleeding. You still have to turn off the key to avoid the ABS pump from pressurizing the accumulator. Implement the bleeding specified by the manufacturer, which for GM vehicles typically is starting with the right rear, then the left rear, right front, and the left front.

If you changed the master cylinder or the ABS modulator, or if there is air trapped in either, you will need to bleed specifically the ABS modulator using a certain method. Here’s what you do for older GM vehicles with the Powermaster III ABS system.

  1. To bleed the isolation valves in the modulator, use two bleeder screws. Start with the nearest one to the engine. Turn on the ignition and gently press the brake pedal. Then, open the bleeder screw until the fluid flows clear. Close it and follow with the second screw.
  2. The first step is to release the pressure by pumping the pedal 40 times with the key off. Wait for approximately 2 minutes for the brake fluid to rest, then refill the fluid reservoir with DOT 3 brake fluid.
  3. To bleed the boost section, press the brake pedal moderately and turn the ignition on for three seconds then off. Repeat this process 10 times. Make sure the pedal feels firm afterward, and take the car for a road test to ensure the brakes are working smoothly.

Note: If you have a Tech 2 scan tool, the solenoid bleed test option is provided to you so as to purge the air from the booster by cycling the hold and release solenoids.

Brake Fluid DOT 3

How To Bleeding Dodge Truck Kelsey-Hayes 4WAL ABS Brakes

The info came from the Dodge Technical Service Bulletin 05-03-94 about the Kelsey-Hayes 4WAL ABS system.

If you haven’t installed the new ABS valve on the front, you can bleed the brakes manually using vacuum equipment or a pressure bleeder. Here’s the sequence: first work on the master cylinder, then go to the rear anti-lock valve, proceed to the combination valve, work on the front anti-lock valve, the left rear wheel, the right rear wheel, the right front wheel, and end with the left front wheel. Make sure to bleed only one valve or all four wheel brakes at a time.

Make sure to bench bleed it before installing if you’ve decided to replace the master cylinder.

Now if you talk about changing the front ABS valve things are going to be very complex. Here’s what you need to do:

  1. Loosen the bleed plug on the new front valve by about a quarter to one full turn. This allows proper bleeding of both upper and lower sections of the valve.
  2. Open the valve cover cap.
  3. Use a VDT 6670 Tool to pull in the bleed valve stem (open position). The bleeding is done in a way that the upper section of the valve assembly is completely flushed.
  4. To hold the stopped valve in the bottom position, rotate and adjusting ring on the blow tool until it presses the valve stem in approximately 0.51 to 0.76 mm (0.020 to 0.030 in.).
  5. Press the brake pedal. You will notice a significant drop of the spindle when the bleed plug is perfectly open and the tool is properly seated on the bleed valve stem.
  6. Do a quick 5-10 pump of the brake pedal (from the low to the high position of the valve) to give both upper and lower section of the valve time to fill with air.
  7. Bleed the new valve assembly at the brake line fitting one by one. Make sure you close the valve bleeder plug after you press the brake pedal every time. Keep bleeding until the fluid flowing from fittings is clear and bubble-free.
  8. Remove the depressor tool from the valve stem and put the cap back on. Then, tighten the bleed plug to 7-9 Nm (60-84 in.-lbs) torque.

Note: You don’t need to open the bleed plug or bleed valve during bleeding, if there the original front ABS valve assembly is still installed. Simply bleed the valve assembly one brake line fitting at a time.

Always check the factory service manual for any special procedures or tools required when working on ABS brakes.