Dynamic Stability Control System Components
Dynamic Stability Control System Components
Hydraulic Modulator
The ECU is integrated into the hydraulic modulator as one compact unit. This reduces the size and wiring required for DSC operation. Additionally the motor relay and valve relay have been replaced by solid state final stages in the control module. The ECU and Hydraulic modulator are available as separate service components. The hydraulic unit to uses:
^ Two pre-charge solenoid valves
^ Two change over solenoid valves
^ Four intake solenoid valves
^ Four outlet solenoid valves
^ One return pump
Pre-Charge Pump
The pre-charge pump is located adjacent to the brake servo on the inner wing (handed).
At low brake fluid temperature the pre-charge pump removes back pressure from the master cylinder) sucks fluid from the reservoir and adds it directly into the circuit. The pump is always used for 3SC, HDC and ETC operation and is controlled by the ABS ECU.
Dynamic Stability Control Sensor
Located under the center console, the dynamic stability control sensor provides two inputs to the ABS ECU, lateral acceleration and rotational rate. The sensor is isolated from body/chassis vibrations through its rubber mounting.
For rotational speed, the sensor produces a reference signal of 2.5 volts and a linear voltage signal from 0.7 to 4.3 volts. This linear voltage input signal is used by the ABS ECU as the degree of rotational rate (yaw).
The sensor also produces a linear voltage signal for the lateral acceleration that ranges from 0.5 to 4.5 volts. The ABS ECU uses this input to determine the side forces acting on the vehicle for DSC regulation.
The DSC sensor has diagnostic capability via the ABS ECU through Test Book/T4.
The DSC sensor is also supplies the air suspension ECU cornering information.
Brake Pressure Sensor
A brake pressure sensor is installed in the hydraulic unit to determine the degree of pressure build up in the braking system. It is installed in the front axle brake circuit.
The sensor receives its power supply from the ABS ECU and produces a linear voltage input signal ranging from 0.5 to 4.5 volts depending on the brake pressure in the circuit.
The brake pressure sensor is used for emergency brake assist and to calculate brake torque applied to each wheel for all DSC functions. Torque is calculate using engine torque from the ECM, gear selected from the EAT ECU and range selected from the transfer box ECU. The sensor is also used for brake temperature calculation.
HDC switch
The Hill Descent Control function is activated by operating the HDC switch located to the left of the gear selector. The green HDC information lamp in the instrument pack, will illuminate when the system is selected and available.
If the vehicle is outside of normal HDC operating parameters, the lamp only illuminates when switch is held. Message center displays the message "NO HDC SLOW DOWN".
DSC Switch
The DSC system is active wherever the ignition is switched on. When pressed,the switch provides a momentary 12 volt signal to the ABS ECU to switch the off the DSC function (DSC indicator in cluster illuminated.) When pressed again, the DSC function switches back on (DSC Indicator in cluster goes off.)
The DSC function can determine if the vehicle is close to roll over and will cut engine torque to ensure that vehicle speed does not increase, thus reducing the chance of vehicle rolling over.
If the DSC function fails, the air suspension drops to between standard and motor way height, to provide increased stability.
Wheel Speed Sensors
The wheel speed sensors are 2 wire Hall Effect type sensors. These sensors picks up on a 48 pulse incremental wheel speed sensor pole wheel on the drive shaft. 48 pulses = one complete wheel revolution. The sensor receives a stabilized 8 volt power supply to hall element on one wire, ground path for sensor through second wire back to the ABS ECU. The signal is generated by the pulse wheel affecting voltage flow through the hall element creating a low of 0.75 and a high of 2.5 volts. The sensors provide immediate vehicle speed recognition.
Steering Angle Sensor
The Steering angle sensor is mounted et the bottom of the steering spindle et the tease of the upper steering column assembly.
The sensor is equipped with a processor and is directly linked to the CAN bus to communicate with the ABS ECU.
The sensor utilizes two potentiometers to determine the steering angle and the rate of steering. These are the raw signals the steering angle microprocessor utilizes to create the steering angle signal for broadcast on the CAN bus.
The sensor requires calibration after repairs to the steering or suspension system. Once the calibration is completed the sensor now also sends an identification number over the CAN bus to the ABS ECU. The ID provides confirmation in the ABS ECU that the steering angle sensor is properly calibrated.
If the ID differs due to component replacement it will be necessary to enter the diagnostic system of the ABS system to initiate the steering angle sensor calibration. DSC will not be available on the vehicle until the steering angle sensor is calibrated. Once complete a new ID number is penetrated end the DSC ECU and Steering angle sensor are properly mated.
The DSC logic checks the plausibility of the steering angle sensor against the other DSC inputs (front wheel speeds, rotation and USC sensor). If battery voltage is interrupted, the current steering wheel rotation is recalculated by the ABS ECU evaluating the wheel speeds.
Replacement steering angles sensors must be coded when installed in the vehicle prior to the calibration procedure in order to add the VIN to the angle sensor. Re-calibration is carried out by turning the steering lock to lock with the engine running while stationary.
Brake Fluid Level Warning Switch
A fluid level switch is incorporated into the reservoir cap.
^ With sufficient fluid level the reed contact is closed
^ When level drops below allowable limits, switch opens.
Since the normal position is closed, this circuit is monitored for shorts to + and ground.
The ABS ECU monitors the fluid level and issues a low fluid level message on the CAN.
The LCM receives the message and illuminates the warning lamp and generates the low brake fluid message for the message center. If the ground signal is momentary, the LCM signals the Instrument cluster of the condition. The instrument cluster then informs the ABS ECU over the CAN bus. If the signal is received prior to the activation of the pre-charge pump, the pre-charge pump activation is delayed.
If the signal is present for more then 25 seconds, the LCM issues two I BUS messages for the Instrument Cluster:
^ Post "Brake Fluid Level" in the Message center
^ Notify the ABS via CAN that the Fluid level has been low for more than 25 seconds.
The ABS ECU immediately switches DSC functions off and continuously illuminates the DSC indicator in the cluster.
DSC System Warning Lamps
Instrument Pack Warning Lamps
The following table describes the warning lamps, their associated faults and system response.
ABS Modulator
The ABS modulator controls the supply of hydraulic pressure to the brakes in response to inputs from the ABS ECU. The modulator is attached by three mounting bushes to a bracket on the LH inner wing, and connected to the primary and secondary hydraulic circuits downstream of the master cylinder assembly. Two electrical connectors link the ABS modulator to the vehicle wiring. Internal passages in the ABS modulator, separated into primary and secondary circuits, connect to the various components that control the supply of hydraulic pressure to the brakes. Valves and check valves control the flow through the internal circuits. A damper chamber and restrictor are included in each circuit to refine system operation. Inlet and outlet solenoid valves control the flow to the individual brakes. An expansion chamber is connected to each circuit to absorb pressure. A return pump is connected to both circuits to provide a pressure source.