According to national standard GB 7258-2017, what happens when pneumatic brake system pressure drops below the statutory low-pressure warning threshold (< 0.55 MPa / 5.5 bar) while driving?

1. A continuous acoustic buzzer and red dash warning light activate; if pressure depletes further, the spring brake chambers (断气刹) will automatically lock the rear wheels
2. The engine automatically increases power by 50% to pressurize the cabin
3. The trailer automatically uncouples and ejects from the fifth wheel
4. The steering wheel automatically rotates 90 degrees to steer the truck into the ditch