Antilock Brake System OBD (ABSO) Module

Refer to COMPONENT INDEX .

The ABSO module is mounted to the ACU together forming the EBB. The ABSO module is a micro-controller based device which monitors the antilock brake system during normal braking and controls it when the vehicle is in an ABS stop. The ABS function avoids wheel lock during braking maneuvers, maintaining the direction of the vehicle, and optimizing stopping distance.

The primary functions of the ABSO module are to:

• Monitor the antilock brake system for proper operation
• Detect wheel locking or wheel slipping tendencies by monitoring the speed of all four wheels of the vehicle
• Control fluid modulation to the wheel brakes while the system is in an ABS mode
• Store diagnostic information
• Provide communication to the diagnostic scan tool while in diagnostic mode
• Illuminate the ABS, ESC, or Brake warning indicator lamp when the system is faulted.
• Illuminate the ESC function lamp when a vehicle dynamic event is occurring
• Provide vehicle speed information, by monitoring the wheel speed sensors, to all modules on the Controller Area Network - Chassis (CAN-C) bus

The ABSO module constantly monitors the antilock brake system for proper operation. If the ABSO module detects a fault, it will turn on a warning indicator lamp and disable the antilock braking system. The normal base braking system will remain operational.

The Hybrid Control Processor (HCP), which is located within the Power Inverter Module (PIM), provides consistent brake system regeneration capacity to the ABSO module. When the brakes are applied, the brake system informs the HCP how much load to put on the P2 in order to attain proper wheel torque to slow the vehicle. When regeneration capacity is maxed out, the base brake system will apply standard foundation brakes. The ABSO provides consistent brake pedal pressure to the driver regardless of whether the braking is through friction, regenerative or a combination of both.

The ABSO module receives the driver requested brake demand requested torque and the capacity of regenerative braking that can be achieved. The ABSO module uses this information to calculate and request the appropriate regenerative brake torque and applies the appropriate amount of friction brake torque to meet the total driver requested brake torque. The ESC can choose when to use regenerative braking, friction braking, or a blended combination of both. Regenerative braking does not affect vehicle braking performance, pedal effort or stopping distance.

The HCP does not request regenerative braking power that is larger than the power boundary of the high voltage battery. The HCP does not process a regenerative braking torque request that is larger than the e-motors torque limits. The electric motor(s) capacity will be determined based upon the thermal characteristics of the motor(s) at the time of a regenerative brake request. The HCP does not send a request to the ESC a regenerative braking torque capacity that is larger than can be achieved by the electrified powertrain.

The ABSO module does not request regenerative braking when any of the following conditions are true:

• ABS is active
• Traction Control (TC) or Anti Spin Regulation (ASR) is active
• Neutral gear is selected
• Instability conditions are detected
• ABSO module fault that prevents regenerative braking

The HCP does not enable normal regenerative braking when any of the following conditions are true:

• Vehicle speed is greater than the maximum regenerative speed
• Vehicle speed is less than the minimum regenerative speed
• Cyclic Redundancy Check (CRC)/Message Counter (MC) failure
• Vehicle shift lever position is in neutral or reverse

MAX Regeneration 

The driver has the ability to preselect the desired braking effect of the P2. By pressing the MAX Regeneration button in the Integrated Center Stack (ICS), the capability of regenerating braking can be switched from "Normal Coasting Regeneration" to "Aggressive Coasting/MAX Regeneration". When MAX Regeneration is turned ON, it will latch for any key cycles that occur and will remain ON until the system enters non-recoverable fault or the driver presses the button to deactivate the feature. MAX Regeneration is a functional process brought about through the interface of the HCP/PIM, Engine Control Module (ECM) and ABSO module when there are not other external functionalities requesting propulsion to the electric powertrain (for example, cruise control, advanced driver assistance system, and others).

The MAX Regeneration switch in the ICS is a momentary push, latching, Local Interface Network (LIN) bus switch and sends its signals to the BCM. The BCM broadcasts the signals on the Controller Area Network - Interior High Speed (CAN-IHS) data bus for other modules on the CAN to use. The switch has an LED indicator to confirm the system is in MAX Regeneration and will be in one of three states:

• MAX Regeneration OFF - No illumination
• MAX Regeneration ON - Constant illumination
• MAX Regeneration Unavailable - Blinking illumination

The HCP performs short to high, short to ground, Signal Not Acquired (SNA) and stuck switch diagnostics for the MAX Regeneration switch my monitoring CAN signals.

The HCP uses the following conditions to determine the algorithm requirements for the MAX Regeneration system:

• Ignition in RUN
• Powertrain propulsion capable - Drive Ready
• No HCP faults active
• No ECM fault active
• No Transmission Control Module (TCM) fault active - vehicle not in Limp Home Mode
• No loss of communication between ECM, BCM, TCM or ABSO module
• HCP State of Charge (SOC) is within the Min/Max thresholds
• ABSO module is ready, active and has no faults
• Vehicle speed is within the calibrated limits of the MAX Regeneration system
• Transfer case is not in Neutral
• Transmission gear is not Park/Neutral
• HCP internal regen brake torque capacity is greater than the "aggressive minimum pedal" value from the ECM
• MAX Regeneration button is not stuck or faulted
• Driver has requested MAX Regeneration through the button in the ICS

There are four MAX Regeneration states:

• MAX Regeneration possible - button LED on continuously, Instrument Panel Cluster (IPC) telltale green (engaged), IPC poppup message "Max Regeneration ON"
• MAX Regeneration Recoverable - button LED on continuously, IPC telltale white (enabled), IPC poppup message "Max Regeneration ON"
• MAX Regeneration Non-Recoverable - button LED blinking, IPC telltale OFF, IPC poppup message "Max Regeneration Unavailable"
• Driver Request MAX Regeneration OFF - button LED OFF, IPC telltale OFF, IPC poppup message "Max Regeneration OFF"

If the driver turns the MAX Regeneration button OFF and the ABSO module is sending a "skid" message, then the HCP will set the button LED blinking and the IPC poppup message to "Max Regeneration ON".

The ABSO module will activate the brake lights whenever the deceleration rate exceeds the threshold of deceleration speed, whether braking is done through the regeneration system or the main braking system has been engaged to stop the vehicle.

The standard ESC system is a four-channel independent control to all four corners of the vehicle, with a active handling system that links the vehicle dynamic control systems to assist the driver in maintaining control under demanding or adverse conditions. ESC primarily integrates the ABS and TC systems to control all four corners of the vehicle in response to yaw and in relation to steering input. The system algorithm determines when to activate the system based on data from the vehicle sensors: wheel speed, yaw rate, lateral acceleration, master cylinder pressure, steering wheel angle and vehicle velocity.

The ABSO module continuously monitors the speed of each wheel through the signals generated by the wheel speed sensors to determine if any wheel is beginning to lock. When a wheel locking tendency is detected, the ABSO module commands the coils to actuate. The coils then open and close the valves in the ABSO module that modulate brake fluid pressure in some or all of the hydraulic circuits. The ABSO module continues to control pressure in individual hydraulic circuits until a locking tendency is no longer present. The ABSO module contains a self-diagnostic program that monitors the antilock brake system for system faults. When a fault is detected, a warning indicator lamp is turned on and a Diagnostic Trouble Code (DTC) fault is then stored in a diagnostic program memory. A latched fault will disable certain system functionality for the current ignition cycle. An unlatched fault will disable certain system functionality until the fault condition disappears. These DTCs will remain in the ABSO module memory even after the ignition has been turned off. The DTCs can be read and cleared from the ABSO module memory by a technician using a diagnostic scan tool. If not cleared with a diagnostic scan tool, the fault occurrence and DTC will be automatically cleared from the ABSO module memory after the identical fault has not been seen during the next 3, 500 miles. Drive-off may be required for the amber ABS warning indicator lamp to go out on the next ignition cycle.