Acura RL (1996-2004 year). Manual — part 521
Anti-lock Brake System (ABS)
Features/Construction
When the brake pedal is pressed during driving, the wheels can lock before the vehicle comes to a stop. In such an event,
the maneuverability of the vehicle is reduced if the front wheels are locked, and the stability of the vehicle is reduced if the
rear wheels are locked, creating an extremely unstable condition. The ABS precisely controls the slip rate of the wheels to
ensure maximum grip force from the tires, and it thereby ensures maneuverability and stability of the vehicle.
The ABS calculates the slip rate of the wheels based on the vehicle speed and the wheel speed, then it controls the brake
fluid pressure to attain the target slip rate.
Grip Force of Tire and Road Surface
Slip Rate
COEFFICIENT OF
FRICTION
TARGET SLIP RATE
SLIP RATE
ROTATIONAL
DIRECTION
RADIAL
DIRECTION
OF THE
ROTATIONAL
DIRECTION
BRAKING
START POINT
A: Distance without slip
B: Slipped distance
C: Actual distance
NO: Normally Open
NC: Normally Closed
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Anti-lock Brake System (ABS)
Features/Construction (cont'd)
ABS Control
The ABS control unit detects the wheel speed based on the wheel sensor signal it received, then it calculates the vehicle
speed based on the detected wheel speed. The control unit detects the vehicle speed during deceleration based on the
rate of deceleration.
The ABS control unit calculates the slip rate of each wheel, and it transmits the control signal to the modulator unit
solenoid valve when the slip rate is high.
The pressure reduction control has 3-modes: pressure reduction, pressure retaining, and pressure intensifying.
ABS CONTROL UNIT
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Self-diagnosis
1. The ABS control unit is equipped with a main CPU and a sub CPU, that check each other for problems.
2. The CPUs check the circuit of the system.
3. Self-diagnosis can be classified into 2 categories.
Initial diagnosis: Performed right after the engine starts and until the ABS indicator goes off.
Regular diagnosis: Performed right after the initial diagnosis until the ignition switch is turned OFF.
4. When a problem is detected by self-diagnosis, the system:
Turns the fail-safe relay OFF
Turns the solenoid valve OFF
Turns the pump motor OFF
Turns the ABS indicator ON
Self-diagnosis Table
Diagnostic Trouble
Code(DTC)
11, 13, 15, 17
12,14,16,18
21-24
31-38
41-44
51
52
53
54
61
62
71
81
Detection Item
Wheel sensor (open/short to body ground/short to power)
Wheel sensor (electrical noise/intermittent Interruption)
Pulser
Solenoid (short to body ground/short to wire)
Wheel lock
Motor lock
Motor stuck OFF
Motor stuck ON
Fall-safe relay
Low ignition voltage
High ignition voltage
Different diameter tire
Central Processing Unit (CPU) diagnosis, and ROM/RAM diagnosis
Detection
Timing
Initia
l
Diagnosi
s
O
O
O
O
Regula
r
Diagnosi
s
O
O
O
O
O
O
O
O
O
O
O
O
Fail-safe Mode
A
S, A and L, S and L
A and L
S
A and L
S and L
A and L
A and L
S
B
B
S
S
Operation Mode Table
Operation
Mode
Regular
operation
Fail-safe
mode-S
Fail-safe
mode-A
Fail-safe
mode-L
Fail-safe
mode-B
Description
Operation in normal condition
The ABS control unit turns the system off when the control unit detects a problem.
If the ABS control unit detects a malfunction during an emergency stop, it will turn off the malfunc-
tioning component, and continue to modulate the rest of the ABS system until the vehicle comes to
a stop. At that, the entire system will be turned off until the problem goes away.
The ABS control unit stores a DTC in back-up memory when it detects a problem. If a problem is
detected when the ignition switch is turned ON (II), the ABS control unit will turn the system off. If
the problem goes away, the ABS control unit will turn the system on again.
The ABS control unit will turn the system off if ignition voltage drops, and will turn on again when
ignition voltage returns to normal.
ABS Indicator
OFF
Comes ON when a
problem is detected.
Comes ON when a
problem is detected.
ON
Comes ON when a
problem is detected.
On-board Diagnosis Function
The ABS control unit is connected to the 16P Data Link Connector.
The ABS can be diagnosed with the Honda PGM Tester.
The ALB Checker cannot be used with this system. For air bleeding, and checking wheel sensor signals, use the Honda
PGM Tester. See the Honda PGM Tester user's manuals for specific operating instructions.
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Table of Contents
Anti-lock Brake System (ABS)
Features/Construction (cont'd)
ABS Modulator
The ABS modulator consists of the inlet solenoid valve, outlet solenoid valve, reservoir, pump, pump motor and the
damping chamber.
The modulator reduces the caliper fluid pressure directly. It is a circulating-type modulator because the brake fluid circulates
through the caliper, reservoir and the master cylinder.
The hydraulic control has three modes: pressure reduction, pressure retaining and pressure intensifying.
The hydraulic circuit is the independent four channel-type, one channel for each wheel.
SOLENOID VALVE
PUMP
MOTOR
IN: INLET VALVE (NORMALLY OPEN)
Pressure intensifying mode: Inlet valve open, outlet valve closed OUT: OUTLET VALVE (NORMALLY CLOSED)
Master cylinder fluid is pumped out to the caliper.
Pressure retaining mode: Inlet valve closed, outlet valve closed
Caliper fluid is retained by the inlet valve and outlet valve.
Pressure reduction mode: Inlet valve closed, outlet valve open
Caliper fluid flows through the outlet valve to the reservoir.
When starting the pressure reduction mode, the pump motor is ON.
When stopping ABS operation, the pump motor is OFF.
The reservoir fluid is pumped out by the pump, through the damping chamber, to the master
cylinder.
Motor operation mode:
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