OPERATION
5-54 / Driving the Vehicle
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5-29.4 Traction Control (Optional)
Automatic Traction Control (ATC) is an optional feature of the ABS system. ATC operates in two ways:
• It applies the service brake to a spinning wheel so that the torque can be transferred through the differential to
the wheel that has the traction.
• It reduces engine torque when both wheels are spinning to improve traction.
The ATC light located in the cab will light when the ATC feature is active.
A traction control switch is provided with the ATC option. This function increases available traction on extra soft
surfaces like snow, mud, or gravel by slightly increasing the permissible wheel spin. When this feature is selected,
the ATC indicator light will blink continuously.
NOTE: For 4x4 vehicles with Electronic Stability Control (ESC), the ATC system is only active in 4x4 mode.
Refer to Table 5-9 for additional information.
Table 5-9: ATC Light Operation - 4x4 Chassis with ESC
5-29.5 Parking Brakes
All Pierce Custom Chassis are equipped with spring brakes on the rear axles for parking. The spring brakes are
applied by operation of the yellow parking brake valve. These brakes are intended to hold the vehicle in a parked
position or to assist in bringing it to an emergency stop and should not be used for normal driving.
If air pressure is lost in the rear service brake section, the spring brakes will be modulated by pressure from the front
brake section allowing a few brake applications before the spring brakes are automatically applied. If air pressure is
reduced to approximately 40 psi in both systems, the spring brake valve will automatically apply.
Mode ATC Light ATC Status ESC Status
4x2 ON OFF ON
4x4 OFF; flashes when
system is active
ON ON
Uncontrolled Vehicle Hazard
Never park vehicle on a steep grade.
Before leaving driver seat ALWAYS:
• Set parking brake.
• Turn front wheels in the direction of the curb.
Immediately after leaving the driver seat:
• Block wheels with adequate wheel chocks.
Failure to follow these procedures may lead to loss of vehicle control, property damage, personal
injury, or death.
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