Brake Booster Inspection

Special Tools Required
Vacuum gauge (  07404-5790301)

Pressure gauge (  07406-5790201)
Attachment (  07410-5790101)
Tube joint adapter (  07410-5790501)
Pressure gauge joint pipe (  07510-6340101)

Leak Test

1.Install the vacuum gauge (A) between the brake booster and check valve.


2.Start the engine, adjust the engine speed with the accelerator pedal so that the vacuum gauge readings show 40.0-66.7 kPa (300-500 mmHg, 11.8-19.7 in.Hg), then stop the engine.

3.Read the vacuum gauge.

If the vacuum reading decreases 2.7 kPa (20 mmHg, 0.8 in.Hg) or more after 30 seconds, check following parts for leaks.
  • Check valve
  • Vacuum hose, pipe
  • Seals
  • Brake booster
  • Master cylinder

NOTE: Do not try to disassemble the brake booster. Replace the brake booster as an assembly with a new one.

Function Test

1.Install the vacuum gauge as same as the leak test.

2.Connect the oil pressure gauges (A) to the master cylinder using the attachments (special tools) as shown.

3.Bleed air through the valves (B).


4.Start the engine and let it idle.

5.Have an assistant depress the brake pedal with a 98 N (10 kgf, 22 lbf) and 294 N (30 kgf, 66 lbf) of pressure measuring with a commerciallly available pressure gauge (A).


6.The following pressures should be obseved at the pressure gauges in each vacuum.

Vacuum booster Vacuum kPa(mmHg, in.Hg) Brake pedal pressure N
(kgf, lbf) 
Master cylinder
oil pressure kPa
(kgf/cm2, psi) 
With ABS Without ABS 
0 (0, 0) 98 (10, 22) 0 (0, 0) 
294 (30, 66) 1,920 (19.6, 280) 
66.7 (500, 19.7) 98 (10, 22) 6,330 (64.5, 920) 
294 (30, 66) 12,130 (123.7, 1,760) 

7.Inspect the master cylinder for leaks if the readings do not fall within the limits shown above.

Booster Check Valve Test

1.Disconnect the brake booster vacuum hose (check valve built in) (A) at the booster side.


2.Start the engine, and let it idle. There should be vacuum available. If no vacuum is available, the check valve is not working properly. Replace the brake booster vacuum hose and check valve, and retest.