ABS-ECU



  • By integrating ABS-ECU into the hydraulic unit, no more wiring harnesses for sending signal that operates the solenoid valve and pump motor is required, assuring higher reliability.
  • Self-diagnostic programs and memory functions are integrated into ABS-ECU. If any malfunction is detected by the self-diagnostic function, ABS-ECU activates a fail-safe function and illuminates ABS warning lamp and brake warning lamp*.
    note *: ABS-ECU illuminates the brake warning lamp as EBD control warning lamp.
  • ABS-ECU detects vehicle speed from the wheel speed sensor signal, recognizes the wheel rotation, estimates the wheel slip condition based on the preprogrammed algorithm, and then controls the solenoid valve in the hydraulic unit so that the wheels do not lock.

ABS FLUID PRESSURE CONTROL


ABS CONTROL CYCLE





  1. ABS control cycle

    1. ABS-ECU calculates the speed and deceleration of each wheel based on the signals from the four wheel speed sensors, and estimates the vehicle speed at that time.
    2. When the brake pedal is depressed, the brake fluid pressure applied to the wheel cylinder increases, and the wheel speed decreases. When the difference between the wheel speed and vehicle speed increases, and the wheel deceleration exceeds the specified point (Point A), ECU judges that the wheels are about to be locked. At this time, ECU reduces the brake fluid pressure by sending the pressure decrease signal to the solenoid valves (IN, OUT). (between a and b)
    3. When the wheel deceleration begins recovery, and the wheel speed reaches the point B, the ECU outputs the pressure hold signal to maintain the wheel cylinder fluid pressure. (between b and c)
    4. When the wheel deceleration is further recovered and overpasses the point C, the ECU determines that the wheel lock possibility has been eliminated and increases the brake fluid pressure by sending the pressure increase signal again. (between c and d)
    5. Brake fluid pressure is controlled by repeating the increase and hold of the pressure. (between d and e)
    6. When the wheel deceleration exceeds the specified point again, ABS-ECU controls the brake fluid pressure by repeating the cycle (Steps 2 to 5).
      note The response of the vehicle wheel speed is slightly delayed in relation to the brake fluid pressure change. This is because the inertial force is applied to the wheels.
  2. Four-wheel control
    This ABS uses a 4-sensor system that controls the right and left front wheels independently of each other and controls the rear wheels simultaneously (select low control).
  3. Available vehicle speed for ABS
    ABS is available with the vehicle speed of approximately 10 km/h or more.

FOUR-WHEEL CONTROL

ABS fluid pressure is controlled independently for four wheels.

EBD FLUID PRESSURE CONTROL





INITIAL CHECK


*
note *: ABS warning lamp may stay ON after the ignition switch is turned ON until the startup vehicle speed reaches approximately 10km/h. As far as ABS-ECU memorizes any diagnosis code related to the wheel speed sensor malfunction recorded during previous ignition ON status, ABS-ECU continues illuminating ABS warning lamp until it verifies that the malfunction for that code is resolved (Startup check.)

STARTUP CHECK




  • Motor, solenoid valve check (only in initial startup*)
    Operates the motor relay in ECU and checks the pump motor operation. At the same time, ABS-ECU sequentially energizes each solenoid valve in a very short period and checks the valve operation.
    note *: Initial startup indicates a first startup after the system has started.
  • Wheel speed sensor check
    ABS-ECU checks for any wheels that have not received wheel speed sensor signal from the startup.

CONSTANT CHECK




  • ABS-ECU
    Performs self-diagnosis in ECU.
  • ECU power supply
    Checks if ECU power supply voltage reaches within the operational range.
  • Wheel speed sensor

    • Monitors the output voltage of the sensor signal wiring harness and checks for abnormal output voltage (open/short circuit.)
    • Checks for any wheels that do not send pulse signal while the vehicle is in motion.
    • Checks if wheel speed which is abnormally higher or lower than the vehicle speed is input.
  • Pump motor and solenoid valve
    Checks that ABS-ECU output signal and the operating condition of the pump motor and solenoid valve agree with each other.

FAIL-SAFE FUNCTION


*
note *: ABS-ECU illuminates the brake warning lamp as EBD control warning lamp.
Diagnosis code No.
 Item
 Action during fail-safe operation
ABS control
 EBD control
 Brake warning lamp
 ABS warning lamp
C1200
 Open or short circuit in wheel speed sensor (FR)
 Prohibited
 Abnormality on rear wheels (both right and left): Prohibits
Abnormality other than the above: Backup EBD
 Abnormality on rear wheels (both right and left): ON
 ON
C1201
 Wheel speed sensor (FR) system
C1205
 Open or short circuit in wheel speed sensor (FL)
C1206
 Wheel speed sensor (FL) system
C1210
 Open or short circuit in wheel speed sensor (RR)
C1211
 Wheel speed sensor (RR) system
C1215
 Open or short circuit in wheel speed sensor (RL)
C1216
 Wheel speed sensor (RL) system
C1225
 Wheel speed sensor malfunction
 Prohibited
 Backup EBD
 OFF
 ON
C1226
 Control solenoid valve (FR) pressure holding system
Prohibited
 Prohibited
 ON
 ON
C1231
 Control solenoid valve (FR) decompressing system
C1236
 Control solenoid valve (FL) pressure holding system
C1241
 Control solenoid valve (FL) pressure reducing system
C1246
 Control solenoid valve (RR) pressure holding system
C1251
 Control solenoid valve (RR) pressure reducing system
C1256
 Control solenoid valve (RL) pressure holding system
C1261
 Control solenoid valve (RL) decompressing system
C1266
 Motor system
 Prohibited
 Prohibited
 ON
 ON
C1273
 Motor relay stuck off
 Prohibited
 Prohibited
 ON
 ON
C1274
 Motor relay stuck on
 Prohibited
 Prohibited
 ON
 ON
C1278
 Valve relay system stuck off
 Prohibited
 Prohibited
 ON
 ON
C1279
 Valve relay system stuck on
 Prohibited
 Prohibited
 ON
 ON
C1340
 Stop lamp switch open circuit
 Prohibited
 Backup EBD
 OFF
 ON
C1365*
 Abnormal power supply of G-sensor
 Prohibited
 Backup EBD
 OFF
 ON
C1381*
 Abnormal seizure or transmit error of G-sensor
 Prohibited
 Backup EBD
 OFF
 ON
C1382*
 Abnormal voltage (low voltage) of G-sensor
 Prohibited
 Backup EBD
 OFF
 ON
C1383*
 Abnormal voltage (high voltage) of G-sensor
 Prohibited
 Backup EBD
 OFF
 ON
C1861
 Low voltage at ABS-ECU power supply
 Prohibited
 Prohibited
 ON
 ON
U1073
 Trouble in CAN bus system
 Enabled
 Enabled
 OFF
OFF
note *: Vehicles for 4WD

DIAGNOSTIC FUNCTION




  • Diagnosis code set
  • Service data output
  • Actuator test

DIAGNOSIS CODE SET



note
  • *EEPROM (Electrical Erasable & Programmable ROM): Special type of memory that can be programmed or erased electrically
  • For each diagnostic item, refer to Fail-safe Function.

DATA LIST OUTPUT



Item No.
 Check item
 Check condition
 Normal condition
01
 FL wheel speed sensor
 Perform a test run of the vehicle
 Speedometer display and M.U.T.-III display almost agree with each other.
02
 FR wheel speed sensor
03
 RL wheel speed sensor
04
 RR wheel speed sensor
05
 Power supply voltage
 Always
 Battery voltage
09*1
 G-sensor
 Always
 1.0 - 4.0 V
13
 Stop lamp switch
 The brake pedal is depressed
 ON
The brake pedal is released
 OFF
63*2
 Rear diff lock switch
 When rear differential lock switch is ON
 ON
When rear differential lock switch is OFF
 OFF
note
  • *1:Vehicles for 4WD
  • *2:Vehicles for rear differential lock

ACTUATOR TEST

The M.U.T.-III can be used to force-drive all solenoid valves and the pump motor.
note
  • When ABS-ECU is disabled, the actuator test cannot be performed.
  • The actuator test can be performed only when the vehicle is stationary. When the vehicle speed reaches 10km/h, the forcible actuator operation is disabled.
  • During actuator test, the ABS warning lamp illuminates, and ABS control is prohibited.
Item No.
 Check item
 Drive Contents
01
 Solenoid valve for front-left wheel
 Solenoid valves and pump motor in the hydraulic unit (simple inspection mode)
02
 Solenoid valve for front-right wheel
03
 Solenoid valve for rear-left wheel
04
 Solenoid valve for rear-right wheel