Traction/Stability Control

LEGEND
(1) Vacuum Booster
(2) Vacuum Hose
(3) Tandem Master Cylinder
(4) Primary Brake Circuit
(5) Secondary Brake Circuit
(6) Hydraulic Pump/Motor Unit
(7) Valve Block
(8) ABS/TC Control Module
(9) Ventilated Brake Rotor
(10) Single Piston Caliper
(11) Wheel Speed Sensor
(12) ABS Warning Lamp
(13) Brake Fluid Level Warning Lamp

TRACTION CONTROL
Vehicles with the Traction Control system use the engine management system to control the throttle, fuel and ignition systems to reduce the engine torque, but with individual brake intervention for enhanced control of wheel spin.

As a tire loses adhesion leading to a potential wheel spin situation, the brake line pressure to that wheel is increased by closing the cut-off solenoid valve and starting the motor and hydraulic pump. This draws brake fluid volume from reservoir via the non-actuated master cylinder, cut-off valve and additional pump inlet valve, then pumps it via the solenoid inlet valve to the brake caliper. An amber warning lamp, located at the right hand side of the instrument cluster, flashes at 2Hz during Traction Control operation.

STABILITY CONTROL
Vehicles with the Stability Control system use the engine management system to control the throttle, fuel and ignition systems to reduce engine torque in order to counteract wheel spin.

The Stability Control switch is mounted in the center console and has an LED illuminated Anti-Skid Control Off (ASC OFF). It does not effect the gear shifting except that a message from the BCM that the traction is active, will switch the Traction Control Module (TCM) to select the appropriate traction program.

Following the traction active signal, the TCM will inhibit downshifts/torque convertor lockup and select a single shift pattern tailored to meet the traction system requirements for upshifts. If during acceleration there is a tendency for one of the wheels to spin due to excessive engine torque or loss of adhesion of a tire, it is detected by the wheel speed sensor.

The information is relayed to the Brake Control Module (BCM) which then informs the engine management system to reduce the torque output of the engine. This is performed in three ways; the throttle is moved towards the closed position, the fuel supply is cut-off to the cylinders and the ignition is retarded.

Because of mechanical delays in moving the throttle, the throttle response is slower to work than the fuel cut-off and retarding the ignition. In the event of a tendency for wheel spin, the BCM uses information from the CAN bus to calculate the torque which the engine should produce to prevent wheel spin. Torque reductions are then requested from the ECM via the CAN bus. The throttle is positioned to provide the target torque calculated to prevent wheel spin.

During the transient phase of torque reduction, the ignition will be retarded and the fuel cut-off to the cylinders to reduce the torque to the target value. Once the throttle has reached its new position, both the fuel cut-off and ignition retard will be restored to their previous settings.