Checking Service Brake: High and Low Pressure Tests

Caution: The high- and low-pressure tests (leak checks) must be carried out only when the engine is switched off.





High-pressure test (leak check):
Perform test on both brake circuits.
1st brake circuit, front axle
2nd brake circuit, rear axle.
Unscrew vent plug, connect pressure tester and vent.





Load brake pedal, refer to specification, and block brake pedal with pedal support. After 2 minutes, pressure must not drop by more than 8%.





Low-pressure test:
Perform test on both brake circuits.
Reset pedal support until test pressure in brake system is equivalent to 2 ... 5 bar.
Car and measuring equipment must remain perfectly still as vibrations will distort the result.
Pressure should remain constant during five-minute test.
Check all rubber parts in case of excessive pressure drop.
Bleed brake calipers and wheel brake cylinders after finishing test.