Subaru LEGACY 2002 Quick Reference Index page 385

E: ABS CONTROL MODULE AND HYDRAULIC CONTROL UNIT (ABSCM & H/U)
! ABS CONTROL MODULE SECTION (ABSCM)
The ABSCM contains two microcontrol modules (MCMs) that complement each other. Both the
MCMs process the same program and each MCM monitors the other's outputs. If a mismatch oc-
curs between their outputs, the ABSCM cuts off the system and activate the fail-safe function.
The ABSCM can store a maximum of 3 trouble codes in an EEP ROM. If more than 3 faults have
occurred, only the 3 most recent failures are stored and others are erased. Trouble codes remain
stored until they are internally or externally erased.
The ABSCM has a test routine (sequence control pattern) which facilitates checking of the hydrau-
lic control unit.
! ABS control
Using primarily the wheel speed data from each ABS sensor and secondarily the vehicle deceler-
ation rate data from the G sensor as parameters, the ABSCM generates a simulated vehicle speed
when there is a risk of wheel lock-up. Using the simulated vehicle speed (called "dummy" vehicle
speed) as a reference, the ABSCM determines the state of the wheel in terms of the tendency to-
ward lock-up. If the result shows that the wheels are about to lock, the ABSCM issues commands
to energize or de-energize the solenoid valves and activate the motor pump of the H/U to modulate
the brake fluid pressures that act on the wheel cylinders, thereby preventing the wheels from lock-
ing.
The ABSCM controls the right and left front wheel fluid pressures independently and the rear
wheel fluid pressures based on the wheel which is the most likely to lock (select-low control).
! Functions available using SUBARU select monitor
When the SUBARU select monitor is connected, the ABSCM allows it
! To read out analog data
To read out ON/OFF data
!
To read out or erase trouble code
!
! To read out status information in the event of a fault (Freeze frame data)
To initiate ABS sequence control pattern
!
Indication functions
!
Under the control of the ABSCM, the ABS warning light provides the following three indication
function:
! ABS fault alerting
! Trouble code indication (by flashing in the diagnosis mode)
! Valve ON/OFF indication (when sequence control pattern is initiated)
ANTI-LOCK BRAKE SYSTEM (ABS)
ABS-7
ABS