Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
Inspection Using Simplified Tester
- Before starting this inspection, remove the brake booster check valve from the vehicle and check its operation (Refer to BRAKE PEDAL HEIGHT CHECK ).
- After checking, install the check valve to the vacuum hose and connect it to the vacuum gauge. Install the booster test adapter (Special tool: MB992146) to the brake booster and connect it to the vacuum gauge. Connect the pressure gauge and pedal depression gauge as shown in the figure. Bleed the pressure gauge and then perform the following tests:
- Airtightness test with no load
Start the engine, and stop it when the vacuum gauge indicator has reached approximately -67 kPa (-9.7 psi). The result is judged as "Good" when the drop of the vacuum approximately 15 seconds after the engine was stopped is within -3.3 kPa (-0.5 psi).
- Airtightness test with load
Start the engine and depress the brake pedal with 200 N. Stop the engine when the vacuum gauge indicator reached approximately -67 kPa (-9.7 psi). The result is judged as "Good" when the drop of the vacuum approximately 15 seconds after the engine was stopped is within -3.3 kPa (-0.5 psi).
When one or more of the above check results are judged as "No Good," the vacuum hose or brake booster is suspected faulty.
- Brake booster characteristics test
Perform this test after the above (1) and (2) were performed.
- Non-servo effect test
With the engine stopped, make sure that the vacuum gauge reading is 0 kPa (0 psi). Depress the brake pedal with 100 N and 300 N, and measure the fluid pressure generated.
STANDARD VALUEItem Pedal depression force 100 N 300 N Generated fluid pressure kPa (psi) 200 (29) or more 1,800 (261) or more - Servo effect test
Start the engine. Depress the brake pedal with 100 N and 300 N when the vacuum gauge indicator reached approximately -67 kPa (-9.7 psi), and measure the fluid pressure generated.
STANDARD VALUEItem Pedal depression force 100 N 300 N Generated fluid pressure kPa (psi) 6,050 - 7,950 (877 - 1,153) 10,720 (1,554) or more
- Non-servo effect test
- Airtightness test with no load
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.