Primary and Secondary Air Pressure Gauges
Physical instruments are listed here in alphabetical order. Some are optional and therefore not found in every vehicle. Digital instruments and gauges are described in their ICU section.
Warning: If air pressure falls below minimum pressure, the braking ability of the vehicle will be limited. Slow the vehicle down and bring it to a gradual stop. Do not attempt to move the vehicle until air pressure has risen above the minimum level. Moving a vehicle without adequate braking power could cause an accident resulting in property damage, personal injury, or death.
Air pressure gauges register the pressure in the primary and secondary air systems. See Fig.. Normal pressure, with the engine running, is 100 to 120 psi (689 to 827 kPa) in both systems.
Fig. 1, Analog Combined Application Air Pressure Gauge - ICUC
Note: The low-air warning buzzer only works when the park brake is released. The low-air warning buzzer is silenced when the park brake is set.
If air pressure drops below approximately 70 psi (483 kPa), a warning light illuminates and the driver display shows a warning. A low-air warning buzzer also sounds if the park brake is not set.
Note: If the pressure in both air systems drops below 70 psi, the parking brakes will drag or apply.