Honda Acura NSX 1991 Service Manual page 719

ALB Description
Features/Construction/Operation
Control Unit
The control unit consists of a main function section, which controls the operation of anti-lock brake system, and sub-
function, which controls the pump motor and "self-diagnosis."
1 . Main Function
The main function section of the control unit performs calculations on the basis of the signals from each speed sen-
sor and controls the operation of the anti-lock brake system by putting into action the solenoid valves in the
modulator unit for each front and rear brake.
2. Sub-Function
The sub-function section gives driving signals to the pump motor and also gives "self-diagnosis"
for backing up the anti-lock brake system.
CONTROL UNIT
SPEED
SENSORS
I
PRESSURE SWITCH
PUMP MOTOR
L
Self-Diagnostic Function
Since the anti-lock brake system modulates the braking pressure when a wheel is about to lock, regardless of the driver's
intention, the system operation and the braking power will be impaired if there is a malfunction in the system. To prevent
this possibility, at speeds above 10 km/h (6 mph), the self diagnosis function, monitors the main system functions. When
an abnormality is detected, the anti-lock brake system indicator light goes on.
There is also a check mode of the self-diagnosis system itself: when the ignition switch is first turned on, the anti-lock
brake system indicator light comes on and stays on for a few seconds after the engine starts, to signify that the self-
diagnosis system is functional.
Fail-Safe Function
If an abnormality is detected, the control unit turns off the fail-safe relays and motor relay. In this condition the anti-lock
brake system is prevented from functioning, yet the basic brake system continues to operate normally.
The Anti-lock Brake System Indicator Light Comes On
When the fluid pressure pump runs more than 120 seconds.
2. When the parking brake is applied for more than 30 seconds while the vehicle is being driven.
3.
When the rear wheel(s) is (are) locked more than a specified time.
4. When the wheel rotation signal is not transmitted due to faulty wire or sensor.
5 .
When the operation time of the solenoid valve(s) exceeds a predetermined valve and the control unit finds an open in
the solenoid circuit.
6.
When the output signals from both main functions in the control unit are not transmitted to the solenoid valve(s).
19-32
(cont'd)
L
I
signals, necessary