Bleeding The ABS System

Bleeding the brake lines and components in the ABS system is performed using the common 2-person, manual bleeding method. A vinyl hose should be attached to each bleeder port, with the other end placed into a clear container partially filled with brake fluid.

If only one brake line, caliper or wheel cylinder has been loosened or replaced, then only that individual wheel needs bleeding. If any system component, such as master cylinder, proportioning valve or ABS hydraulic unit has been replaced, the entire system requires bleeding.

When bleeding the entire system, always begin with the wheels in the secondary brake circuit, then proceed to the primary circuit. The correct order is right front, left rear, left front and right rear. When bleeding, slowly depress the brake pedal and hold it down while the bleeder is opened for 1–2 seconds. Close the bleeder and release the pedal. Wait 3–4 seconds before the next pedal application. Rapid pedal pumping will actually complicate the bleeding and extend the procedure. When air bubbles are no longer seen in the escaping brake fluid, tighten the bleeder to 6 ft. lbs. (8 Nm).

If the hydraulic unit has been replaced or drained of fluid, it must be bled using specific procedures. This bleeding is not necessary under normal repair conditions not involving the hydraulic unit. To bleed the hydraulic unit:

1. Bleed the brake lines at all 4 wheels in the normal fashion.
2. Attach the vinyl hose to one of the bleeders on top of the hydraulic unit. Bleed this port in the same fashion as the wheels. Move the hose to the other bleeder port and repeat the bleeding. Both of these ports bleed the primary brake circuit in the actuator — front left and right rear.
3. Remove the cone screw from the secondary bleeder port and install a bleeder screw. Install the clear vinyl tube on the bleeder.
4. Open the bleeder and depress the brake pedal slowly; hold the pedal depressed.
5. With the pedal depressed, intermittently apply the AV electrical signal to the solenoid valve. To apply the AV signal:
   1. Disconnect both battery terminals.
   2. Disconnect the 2-pin and 12-pin connectors at the hydraulic assembly.
   3. At the 12-pin connector, connect terminals 1 and 3 to battery ground. Connect terminals 5 and 7 to the positive terminal of the battery. Take great care not to short terminals 5 and 7 to the grounded terminals nearby.
   4. When the last connection is made, the AV signal is transmitted to the solenoids. Do not send this signal for more than 5 seconds. Break the connection at the positive terminal after 2–3 seconds.
6. When the brake pedal moves to the end of its stroke, close the bleeder and allow the pedal to return. If the AV signal is not transmitted for any reason, the bleeder need not be closed before returning the pedal.
7. Repeat Steps 4, 5 and 6 until the fluid in the tube contains no air.
8. With the AV signal disconnected and the brake pedal released, remove the bleeder fitting and re-install the cone screw. Tighten the cone screw to 6 ft. lbs. (8 Nm).
9. Repeat the procedure from Step 3 for the other secondary bleeder port. Both secondary ports must be bled.
10. Carefully remove the jumper wires from the 12-pin connector. Do not allow the terminals to short to each other or to ground.
11. Connect the 2- and 12-pin connectors at the hydraulic unit. Connect the battery cables with the ignition OFF.