Bleeding Hydraulic Brake Booster

Hydraulic Brake Booster (HBB) system bleeding must be done in the following cases:

• If brake fluid is drained after removing or installing the HBB.
• If there is excessive brake fluid loss during normal brake system bleeding.
• If you suspect that air has entered the HBB system.

HBB system bleeding must be done in the following order:

1. Front brake lines (filling).
2. Accumulator (HBB).
3. Rear brake lines (filling).
4. Power supply (HBB).
5. ABS (HBB).
6. Rear brake lines (bleeding).
7. Front brake lines (bleeding).

1. Fill the front brake system with brake fluid as follows (right front first, left front second):
   1. Attach a clear hose to right front caliper bleeder valve. This helps to monitor air/fluid flow.
   2. Be sure the fluid level is between the "MIN" and "MAX" lines.
   3. Turn the ignition switch to the "LOCK" (OFF) position. Pump the brake pedal 3-4 times and hold it depressed.
   4. Open the right front caliper bleeder valve 1/4 turn.
   5. With the bleeder valve still open, pump the brake pedal repeatedly to fill the line with fluid until no obvious air bubbles are seen. When no more obvious air bubbles are seen, and while the brake pedal is still being pumped, close the bleeder valve.
   6. Repeat steps a  -e  for the left front caliper.
   7. Release the brake pedal when both sides are filled.
2. To fill the pump motor, turn the ignition switch to "ON" position to operate the pump motor. If the pump motor operates normally (normal operation sound), go to next step. If the pump motor operation sound is dry and high-pitched, depress the brake pedal 3 or 4 times to introduce fluid into the pump motor, then go to next step.
3. Fill the accumulator system with brake fluid as follows:
   1. Wait for the pump motor to stop from step  2 .
   2. Depress the brake pedal slowly 3 or 4 times with the ignition switch in "ON" position. Observe the condition of the brake fluid in the reservoir. If the fluid is cloudy, leave it for 2 or 3 minutes until it becomes clear. Repeat as necessary until no bubbles appear while pumping the brake pedal.
      NOTE: It is okay to fill the reservoir to the "MAX" line during this process. Brake fluid level around the "MIN" line may cause bubbles to appear from the jet flow of brake fluid while pumping the brake pedal.
4. Fill the rear brake system with brake fluid as follows (right rear first, left rear second):
   CAUTION:

   • If a large quantity of brake fluid is drained during the bleeding procedure, the accumulator pressure will decrease abnormally. Do not bleed more than .11 Qt. (.1 L) from each wheel at a time.
   • Confirm that the pump motor stops after each air bleeding step.
   NOTE: A high-pressure hydraulic noise (hissing) is normal during this procedure.
   1. Attach a clear hose to right rear caliper bleeder valve. This helps to monitor air/fluid flow.
   2. Be sure the fluid level is between the "MIN" and "MAX" lines.
   3. Turn the ignition switch to "LOCK" (OFF) position. Pump the brake pedal 3-4 times and hold it depressed.
   4. Open right rear caliper bleeder valve 1/4 turn.
   5. With the bleeder valve still open, pump the brake pedal repeatedly to fill the line with fluid until no obvious air bubbles are seen. When no more obvious air bubbles are seen, and while the brake pedal is still being pumped, close the bleeder valve.
   6. Repeat steps a  -e  for left rear caliper.
   7. Release the brake pedal when both sides are filled.
5. Supply brake fluid into the power supply system as follows:
   CAUTION: Keep the brake fluid reservoir level just above the "MIN" line at this time. Monitor the fluid level during this procedure to ensure it does not reach below the "MIN" line.
   1. To release the pressure in the HBB power supply system, turn the ignition switch to "LOCK" (OFF) position and depress the brake pedal repeatedly until its depressing force suddenly feels heavy (no pedal travel).
   2. Turn the ignition switch to "ON" position and at the same time quickly depress the brake pedal approximately 20 times. Then confirm that the pump motor has stopped. This can take up to 2 minutes.
   3. Turn the ignition switch to "LOCK" (OFF) position and depress the brake pedal repeatedly until its depressing force suddenly feels heavy (no pedal travel).
   4. Turn the ignition switch to "ON" position to operate the pump motor. Confirm that the pump motor stops within 25 seconds. If the pump motor does not stop, repeat steps a  -c  .
6. Supply fluid into the ABS system as follows:
   CAUTION: When connecting or disconnecting the scan tool, ensure that the ignition switch is at the "LOCK" (OFF) position.
   1. Turn the ignition switch to "LOCK" (OFF) position and connect scan tool MB991502 to the data link connector.
   2. Turn the ignition switch to "ON" position. Select from scan tool menu screen as follows: SYSTEM SELECT, ABS, ACTUATOR TEST, then AIR BLEED.
   3. Depress and hold the brake pedal.
   4. Activate AIR BLEED 1 on scan tool screen. When the scan tool flashes confirmation that the AIR BLEED 1 operation is completed, proceed with AIR BLEED 2.
   5. Depress and hold the brake pedal.
   6. Select and activate AIR BLEED 2 on scan tool screen. When the scan tool flashes confirmation that the AIR BLEED 2 operation is completed, go to next step.
7. Bleed the rear brake system as follows (right rear first, left rear second):
   CAUTION:

   • Keep the brake fluid reservoir level just above the "MIN" line at this time. Monitor the fluid level during this procedure to ensure it does not reach below the "MIN" line.
   • If a large quantity of brake fluid is drained during the bleeding procedure, the accumulator pressure will decrease abnormally. Do not bleed more than 0.1 L (0.11 quart) from each wheel at a time.
   • Confirm that the pump motor stops after each air bleeding step.
   1. Attach the clear hose to right rear caliper to monitor air/fluid flow.
   2. Turn the ignition switch to "ON" position.
   3. Open bleeder valve 1/4 turn.
   4. With the bleeder valve open, pump the brake pedal 3 times and hold.
   5. Close the bleeder valve.
   6. Pump the brake pedal 3 times and hold.
   7. Open the bleeder valve 1/8 turn briefly to allow any remaining air to escape, then close the bleeder valve.
   8. Repeat steps f  and g  as many times as necessary to eliminate all air in the line.
   9. Repeat steps a  -h  at the left rear caliper.
8. Bleed the front brake system as follows (right front first, left front second):
   CAUTION:

   • Keep the brake fluid reservoir level just above the "MIN" line at this time. Monitor the fluid level during this procedure to ensure it does not reach below the "MIN" line.
   • If a large quantity of brake fluid is drained during the bleeding procedure, the accumulator pressure will decrease abnormally. Do not bleed more than 0.1 L (0.11 quart) from each wheel at a time.
   • Confirm that the pump motor stops after each air bleeding step.
   1. Attach the clear hose to right front caliper to monitor air/fluid flow.
   2. Turn the ignition switch to "ON" position.
   3. Open bleeder valve 1/4 turn.
   4. With the bleeder valve open, pump the brake pedal 3 times and hold.
   5. Close the bleeder valve.
   6. Pump the brake pedal 3 times and hold.
   7. Open the bleeder valve 1/8 turn briefly to allow any remaining air to escape, then close the bleeder valve.
   8. Repeat steps f  and g  as many times as necessary to eliminate all air in the line.
   9. Repeat steps a  -h  at left front caliper.
9. Adjust the brake fluid level as follows:
   1. Turn the ignition switch to "LOCK" (OFF) position.
   2. Depress the brake pedal repeatedly (up to 40 times or more) until its depressing force suddenly feels very heavy (no pedal travel).
   3. Release the brake pedal.
   4. Adjust the brake fluid level between the "MIN" and "MAX" lines on the reservoir.