Acura NSX 1991 Manual page 521

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Anti-lock Brake System (ABS) Description
Features/Construction/Operation (cont'd)
ABS Control Unit
The ABS 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 ABS control unit performs calculations on the basis of the signals from each wheel
sensor 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" signals, necessary
for backing up the anti-lock brake system.
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 6 mph (10 km/h), the self-diagnosis function monitors the main system functions. When
an abnormality is detected, the ABS indicator light comes on.
There is also a check mode of the self-diagnosis system itself: when the ignition switch is first turned on, the ABS in-
dicator 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 ABS 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 ABS Indicator Light Comes On
1. 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 ABS control unit finds an
open in the solenoid circuit.
6. When the output signals from both main functions in the ABS control unit are not transmitted to the solenoid
valve(s).
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