Traction Control System Purpose

PURPOSE
The Antilock Brake System (ABS) prevents wheel lock-up under heavy braking conditions on virtually any type of road surface. An ABS brake system is desirable because a vehicle which is stopped without locking the wheels will retain directional stability and some steering capability. This allows the driver to retain greater control of the vehicle during heavy braking.

OPERATION
The Teves Mark IV-G system uses a diagonal split hydraulic brake system. In the standard brake mode the master cylinder primary circuit supplies pressure to the right front and left rear wheel brakes. The master cylinder secondary circuit supplies pressure to the left front and right rear wheel brakes. During an ABS stop the Mark IV-G system uses four channel operation. This means that during antilock operation each wheel brake is independently controlled. By using separate hydraulic channels for stopping each wheel. The system is able to retain directional stability and steering control while applying maximum braking. The system provides maximum braking even when road conditions vary. During an ABS stop, "wheel lock-up" does not necessarily mean that the wheel has stopped turning. It only means that the wheel is turning slower than the vehicle speed. This is called "wheel slip" and is indicated in percent. Zero percent slip means that the wheel is rolling free and one hundred percent slip means that the wheel is locked. The ABS system maintains an average of approximately 15 to 20 percent wheel slip.

COMPONENTS/ACRONYMS
- CAB-Controller Antilock Brake
- HCU-Hydraulic Control Unit
- ABS-Antilock Brake System
- PSI-Pounds per Square Inch (pressure)
- WSS-Wheel Speed Sensor
- FWD-Front Wheel Drive
- DTC-Diagnostic Trouble Code

TRACTION CONTROL FEATURE
The traction control feature is designed to operate at speeds up to approximately 48 KM/H (30 MPH). Traction control can be deactivated via the traction control switch located on the instrument panel. An electronic control module is used to monitor wheel speeds and to modulate (control) hydraulic pressure in each brake channel. The hydraulic pressure is used to prevent wheel lock up during braking, and to maintain traction at the driven wheels by reducing wheel spin.

The Traction Control feature is designed into the ABS system which allows the Controller Antilock Brake to monitor and regulate wheel spin at the driving wheels by applying the brakes at the affected wheels. This limits wheel spin under heavy acceleration, and under normal acceleration on slippery surfaces.

CIRCUIT OPERATION
There are two Anti-Lock Brake Systems (ABS) used in this vehicle. One is the standard system and the other is equipped with traction control.

Power for either of the Anti-Lock Brake Systems (ABS) is supplied by three fuses. There is a 10 amp fuse in cavity 6 of the junction block. Power for the fuse is supplied by circuit A22. This circuit is HOT in the RUN position only.

Power for the A22 circuit is supplied on circuit A2 from the Power Distribution Center (PDC). The A22 circuit is protected by a 40 amp fuse located in cavity J of the PDC.

Circuit F20 connects, from the fuse in cavity 6 of the junction block, to the Controller Anti-Lock Brake (CAB) module and the coil side of the ABS main relay.

The second fuse is located in the PDC cavity C. This fuse powers the contact side of the ABS pump motor relay on circuit A10. This relay is located on the side of the PDC and the fuse is HOT at all times.

The third fuse is also located in the PDC. This fuse is located in cavity I and is used to power the contact side of the ABS main relay This fuse is HOT at all times.

There are three grounding points used for the CAB module. All three of the grounds are on circuit Z1 from the control module to the left front frame rail.