Check ____ to ensure that the air in your vehicle's air braking system flows to all tires.
Check the air brakes on a double or triple combination during your normal pre-trip inspection. After air pressure has reached a normal level, push in the red trailer air supply knob to send air to the emergency lines. Use the trailer hand brake to send air to the service line, then open the rear shut-off valve. If air is escaping through the valve, you will know that the entire system is charged.
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