Lesson 01 · 4 min
Build and read pressure
Explain the service, parking, and emergency functions and decide when a dual air system has enough pressure for checks.
Rule to rememberBuild at least 100 psi in both dual-system circuits before driving, then complete the required brake checks.
Know the functions
The service system responds to the brake pedal. The parking system holds a parked vehicle. The emergency system uses parts of the service and parking systems during a failure.
Read both circuits
A dual system has primary and secondary circuits. Watch both gauges. A released parking brake or an extinguished warning does not prove that both circuits have safe operating pressure.
Why it matters
A low circuit can leave part of the service-brake system without full braking. Build pressure and inspect before movement.