Mazda 3 Service Manual: Power Brake Unit Inspection

NOTE:

• The following inspection methods are simple inspection methods to judge the function of the power brake unit.

• If there is any malfunction in the power brake unit, replace the power brake unit as a single unit.

Without Using SST

Operation inspection

1. With the engine stopped, pump the pedal a few times.

2. With the pedal depressed, start the engine.

3. If the pedal moves down slightly immediately after starting the engine, the unit is normal.

Vacuum function inspection

1. Start the engine.

2. Stop the engine after driving the vehicle for 1—2 min

.

3. Depress the pedal with normal force.

4. If the first pedal stroke is long and becomes shorter with subsequent strokes, the unit is normal.

• If a problem is found, inspect for damage to or improper installation of the check valve and vacuum hose. After repairing, inspect again.

Vacuum loss function inspection

1. Start the engine.

2. Depress the pedal with normal force.

3. With the pedal depressed, stop the engine.

4. Hold the pedal depressed for approx. 30 s

.

5. If the pedal height does not change during this time, the unit is normal.

Using SST

Pre-inspection preparation

1. Install the SST

(49 D043 0A0) to the master cylinder (secondary side) in the orientation shown in the figure.

NOTE:

• When installing the SST

  (49 D043 0A0) to the master cylinder, use a commercially available flare nut wrench.

• Flare nut across flat: 12 mm {0.47 in}

2. Connect the SSTs

, a vacuum gauge, and a pedal force gauge to the master cylinder, and bleed the air from the SSTs

and the brake line. (Bleed the air from the SSTs

using air bleed valve A.)

Checking for vacuum loss (loaded condition)

1. Start the engine.

2. Depress the brake pedal with a force of 200 N {20.4 kgf, 45.0 lbf}

.

3. Stop the engine when the vacuum gauge reading reaches 68 kPa {510 mmHg, 20 inHg}

with the brake pedal depressed.

4. Measure the amount of vacuum decrease for 15 s

immediately after stopping the engine.

5. If the amount of vacuum decrease is 3.3 kPa {25 mmHg, 0.97 inHg}

or less, the power brake unit is normal.

Lack of hydraulic pressure inspection

1. If the pedal force and fluid pressure correlation is within the specification with the engine stopped and a vacuum amount of 0 kPa {0 mmHg, 0 inHg}

, the system is normal. Master cylinder fluid pressure

Hydraulic pressure inspection

1. Start the engine. Depress the brake pedal when the vacuum reaches 66.7 kPa {500 mmHg, 19.7 inHg}

.

2. At this time, apply the indicated pedal force and if the fluid pressure is within the specification, the unit is normal. Master cylinder fluid pressure (MZR 2.0, SKYACTIV-G 2.0, MZR 2.5)