Isuzu N-Series. Manual — part 234
ANTI-LOCK BRAKE SYSTEM (ABS) 5A4-1
BRAKES
SECTION 5A4
ANTI-LOCK BRAKE SYSTEM (ABS)
Contents
GENERAL DESCRIPTION . . . . . . . . . 5A4-3
GENERAL DIAGNOSIS . . . . . . . . . .. 5A4-6
SYMPTOM DIAGNOSIS . . . . . . . . ...5A4-34
DIAGNOSTIC TROUBLE CODES . . . . . 5A4-38
Diagnostic Trouble Codes. . . . . . . ..5A4-38
DIAGNOSIS BY “ABS” WARNING LIGHT ILLUMINA-
TION PATTERN . . . . . . . . . . . . 5A4-39
UNIT INSPECTION PROCEDURE . . . . ...5A4-56
5A4-2 ANTI-LOCK BRAKE SYSTEM (ABS)
ANTI-LOCK BRAKE SYSTEM (ABS) 5A4-3
GENERAL DESCRIPTION
Service Precaution
Caution:
Always use the correct fastener in the proper location. When you replace a fastener, use ONLY the exact part number
for that application. ISUZU will call out those fasteners that require a replacement after removal. ISUZU will also call
out the fasteners that require thread lockers or thread sealant. UNLESS OTHERWISE SPECIFIED, do not use sup-
plemental coatings (Paints, greases, or other corrosion inhibitors) on threaded fasteners or fastener joint interfaces.
Generally, such coatings adversely affect the fastener torque and the joint clamping force, and may damage the fas-
tener. When you install fasteners, use the correct tightening sequence and specifications. Following these instructions
can help you avoid damage to parts and systems.
General Description
The Anti-lock Brake System (ABS) works on all four wheels. A combination of wheel speed sensor and Electronic
Hydraulic Control Unit (EHCU) can determine when a wheel is about to stop turning and adjust brake pressure to
maintain best braking.
This system helps the drive maintain greater control of the vehicle under heavy braking conditions.
Legend
1. Hydraulic Line
7. Load Sensing Proportioning Valve (LSPV)
2. Electronic Line
8. Battery
3. Electronic Hydraulic Control Unit (EHCU)
9. ABS Warning Light
4. Front Wheel Speed Sensor
10. Brake Switch
5. Rear Wheel Speed Sensor
6. Diagnosis Connector
8
ENGINE CONTROLLER
OR
EXH BRAKE CUT RELAY
5
7
4
4
1
3
5
TO EHCU
EHCU
ELECTRONIC HYDRAULIC
CONTROL UNIT(EHCU)
HYDRAULIC UNIT(HU)
2
9
6
ABS
DIAG
TO EHCU
CAB
10
TO EHCU
N5A1001E
5A4-4 ANTI-LOCK BRAKE SYSTEM (ABS)
System Components
The Anti-lock Brake System consists of a Electronic Hy-
draulic Control Unit (EHCU), four Wheel Speed Sensors
and Warning Light.
Electronic Hydraulic Control Unit (EHCU)
The EHCU consists of Electronic Brake Control Module
(EBCM) and Hydraulic Unit (HU).
The EHCU is located at the frame side, in front of rear
spring bracket.
The EHCU consists of ABS control circuits, fault detec-
tor, and a fail-safe. It drives the hydraulic unit according
to the signal from each sensor, cancelling ABS to return
to normal braking when a malfunction has occurred in
the ABS.
The EHCU is self-diagnosing function which can indi-
cate faulty circuits during diagnosis.
Notice:
When disconnecting harness connector from EHCU,
push the tang lock of the connector and release the tang
lock. Then move the lever.
Hydraulic Unit (HU)
It consists of a Motor, Plunger Pump, Solenoid Valves
and Check Valve.
Solenoid Valves: Reduces or holds the caliper fluid
pressure for each front brake or both rear brakes ac-
cording to the signal sent from the EHCU.
Reservoir: Temporarily holds the brake fluid that returns
from the front and rear wheel brake so that pressure of
front wheel brake can be reduced smoothly.
Plunger Pump: Feeds the brake fluid held in the reser-
voir to the master cylinder.
Motor: Drives the pump according to the signal from EH-
CU. Check Valve: Controls the brake fluid flow.
ABS Warning Light
Vehicles equipped with the Anti-lock Brake System has
an amber “ABS” warning light in the instrument panel.
The “ABS” warning light will illuminate if a malfunction in
the Anti-lock Brake System is detected by the Electronic
Hydraulic Control Unit (EHCU). In case of an electronic
malfunction, the EHCU will turn “ON” the “ABS” warning
light and disable the Anti-lock braking function.
The “ABS” light will turn “ON” for 2 seconds after the ig-
nition switch is to the “ON” position, and then will go out.
If the “ABS” light comes “ON” and stays “ON” while driv-
ing, the Anti-lock Brake System should be inspected for
a malfunction according to the diagnosis procedure.
Wheel Speed Sensor
It consists of a sensor and a rotor. The sensor is at-
tached to the knuckle on the front wheels and to the
bracket on the brake back plate on the rear wheels.
The front speed sensor is coil type and rear is Hall IC
type.
The sensor rotors press-fitted to front and rear wheel
hubs output pulse frequency depending on wheel rota-
tion.
The speed sensors find vehicle speed from its frequen-
cy.
Normal and Anti-lock Braking
Under normal driving conditions, the Anti-lock Brake
System functions the same as a standard power assist-
ed brake system. However, with the detection of wheel
lock-up, a slight bump or kick-back will be felt in the
brake pedal. This pedal “bump” will be followed by a se-
ries of short pedal pulsations which occurs in rapid suc-
cession. The brake pedal pulsation will continue ANTI-
LOCK BRAKE SYSTEM (ABS) 5A4-7 until there is no
longer a need for the anti-lock function or until the vehi-
cle is stopped. A slight ticking or popping noise may be
heard during brake applications when the Anti-lock fea-
tures is being used.
Push
Push
Push
Tang lock
Lever
Move lever outside
EHCU
CONNECTOR
N5A1002E
N5A1003E
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