Step 7: Start the Engine and Check Test for Hydraulic Leaks. If the vehicle has hydraulic brakes, pump the brake pedal three times. Then apply firm pressure to the pedal and hold for five seconds. The pedal should not move. If it does, there maybe a leak or other problem. Get it fixed before driving. If the vehicle has air brakes, do the checks described in Sections 5 and 6 of this manual. Brake System Test Parking Brakes) Fasten safety belt Set parking brake (power unit only. Release trailer parking brake (if applicable. Place vehicle into a low gear. Gently pull forward against parking brake to make sure the parking brake holds. Repeat the same steps for the trailer with trailer parking brake set and power unit parking brakes released (if applicable. If it doesn't hold vehicle, it is faulty get it fixed.