Brake System Components
A warning light or ICU text message (ICU4Me only) and buzzer come on if air pressure drops below approximately 70 psi (483 kPa) in either system. See Table.. If this happens, check the air pressure gauges to determine which system has low air pressure. Although the vehicle's speed can be reduced using the foot brake control pedal, either the front or rear service brakes will not be operating at full capacity, causing a longer stopping distance. Bring the vehicle to a safe stop and have the air system repaired before continuing.
Important: In the event of a total loss of service brakes with full system air pressure, use the parking brake control valve (yellow knob) to bring the vehicle to a complete stop in the safest location possible.
Table 1, Brake System Warning and Indicator Lamps
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Brake System Warning and Indicator Lamps |
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Lamp Description |
Color |
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 |
Low Air Pressure (EPA10 and Newer) |
Indicates air pressure in the primary or secondary reservoir has dropped below approximately 70 psi (483 kPa). |
Red |
 |
Low Air Pressure (ICU4Me only, mid-GHG14) |
Indicates air pressure in the primary or secondary reservoir has dropped below approximately 70 psi (483 kPa). |
— |
 |
Parking Brake |
Indicates the parking brake is engaged. |
Red |
 |
Vehicle ABS |
Momentary illumination indicates the vehicle ABS is engaged. Solid illumination indicates a problem with the vehicle ABS. Repair the ABS immediately to ensure full braking capability. |
Amber |
 |
Trailer ABS |
Momentary illumination indicates the trailer ABS is engaged. Solid illumination indicates a problem with the trailer ABS. Repair the ABS immediately to ensure full braking capability. |
Amber |
 |
Wheel Spin |
Flashing indicates the ATC system is active, or the ATC button has been pressed to allow wheel slip. Solid illumination indicates a problem with the ATC system. Repair the ATC system immediately to ensure full braking capability. |
Amber |
 |
Engine Brake |
Indicates the engine brake is enabled. |
Green |
Table 1, Brake System Warning and Indicator Lamps
Before a vehicle with insufficient system air pressure can be moved, the spring parking brakes must be released by applying an external air source at the gladhands, or by manually caging the parking brake springs.
Warning: Do not release the spring parking brakes and then drive the vehicle. There would be no means of stopping the vehicle, which could result in serious personal injury or vehicle damage. Before releasing the spring parking brakes, make the connection to a towing vehicle or chock the tires.
After correcting the brake system problem, uncage the spring parking brakes before resuming normal vehicle operation.
Primary Air Brake System
Loss of air pressure in the primary air system causes the rear service brakes to become inoperative. The secondary air system will continue to operate the front brakes and the trailer brakes (if equipped).
Secondary Air System
Loss of air pressure in the secondary air system causes the front service brakes to become inoperative. The primary air system will continue to operate the rear service brakes and the trailer brakes (if equipped).