sensor ISUZU TROOPER 1995 Owner's Guide

REAR WHEEL ANTILOCK BRAKE SYSTEM 5A3-1
SECTION 5A3
REAR WHEEL ANTILOCK BRAKE SYSTEM
(RWAL}
w CAUTION:
• All brake attaching fasteners are an important attaching part in that they could affect performance of vital
parts and systems, and/or could result in major repair expense. They must be replaced with one of the same
part
number or with an equivalent part if replacement becomes necessary. Do not use replacement parts of
lesser quality or substitute design. Torque values must be used as specified during reassembly to assure
proper retention of these parts.
CONTENTS
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 5A3· 1
General Description . .
. . . . . . . . . . . . . . .
5A3· 1
Rear
Wheel Antilock (RWAL) Control
Parts Location . .

. . . . . . . . . . . . . . . . .
5A3· 5
System Diagram . .

. . . . . . . . . . . . . . . . . . . .
5A3· 6
Rear
Wheel Antilock (RWAL) System
Diagnostics . .

. . . . . . . . . . . . . . . . . . . . . .
5A3· 7
On-Vehicle Service . .

. . . . . . . . . . . . . . . . .
5A3·38
RWAL Electronic Brake Control
Module (EBCM) Replacement ....... 5A3-38
Antilock
(Isolation/Dump) Valve
Replacement ..................... 5A3-39
Speed Sensor Replacement
.......... 5A3-40
Main Data and Specifications ........... 5A3-41
Torque Specifications
............... 5A3-41
INTRODUCTION
This section deals with the complete diagnosis and
services
for vehicles equipped with rear wheel
antilock.
For service information regarding all other
components
of the brake system, refer to "Hydraulic
Brakes"
(Sec. SA), "Brake Booster System" (Sec. SA 1)
or "Disc Brakes" (Sec. SA2) of this Manual.
GENERAL DESCRIPTION
The rear wheel anti lock system (RWAL) is designed to
reduce rear wheel lock-up during a severe brake
application,
thus maintaining rear end stability. The
system functions
by regulating the rear hydraulic
brake line pressure. The pressure regulation is
accomplished
by an anti lock valve which is located on
the
front right side of engine room. The anti lock valve
is made up of two valves, a dump valve which releases
pressure into an accumulator and an isolation valve
which maintains rear brake pressure. The valve is
controlled
by a microcomputer which is part of the
Electronic Brake Control Module (EBCM). The
EBCM is mounted at the
front of the center
console. Under severe brake application, as pressure
is
applied to the brake pedal, the EBCM is designed to
permit the valve to do one of three functions or a
combination
of all three. The EBCM will allow the valve
to either maintain the same amount of hydraulic
pressure, release hydraulic pressure through the
dump valve into the accumulator or increase the
pressure by
pulsing the isolation valve.
The EBCM operates by receiving signals from the
speed sensor (which
is located in the differential
carrier), combination
valve and the brake light switch.
The RWAL system is connected
to the RWAL indicator
light located on the dash. An indication of the RWAL
operation and a
bulb check is performed each time the
ignition is turned
"ON". The indicator light will remain
on
for about two seconds. A RWAL system
malfunction is indicated if the RWAL indicator light
stays on, or comes on during driving. To determine the
specific
trouble, refer to "RWAL System Diagnostics"
in this section.

5A3-2 REAR WHEEL ANTILOCK BRAKE SYSTEM
To front brakes Combination valve
Anti lock valve
Accumulator
•
- -

- -
Electric
.,_ __ Hydraulic
I I I I I ~-------------------1 1--------------------
1_---------------------
Speed sensor
~----1 I
Fig. 5A3-1
12V DC I I
I
I
I
GRND
---, I I I
I
I
--'--
•

REAR WHEEL ANTILOCK BRAKE SYSTEM 5A3-3
ELECTRONIC BRAKE CONTROL MODULE
(EBCM)
The electronic brake control module is microprocessor
based and is located on the
front end of the center
Power source
console. It performs three different algorithms to
calculate excessive wheel deceleration and performs
self check diagnostics.
Ground
~
Wheel speed sensor TACHOMETER
ALGORITHM
Valve reset
Brake
switch
PERFORMANCE
ALGORITHM o-+ ...
Isolation solenoid
Dump solenoid
SELF CHECK AND FAILSAFE
ALGORITHM
Differential switch, br<'!ke warning light
~
Fig. 5A3-2
ANTILOCK (ISOLATION/DUMP) VALVE
The antilock (dual solenoid hydraulic) valve is located
between the rear brakes and the combination valve
and is attached on the
front right side of engine room.
The valve contains
an isolation valve, dump valve and
an accumulator and is electrically connected to the
electronic control module.
The normal positions
for the antilock valve com­
ponents are
as follows;
1. Isolation valve is normally open (flow through
under normal braking).
2. Dump valve is normally closed.
3. Accumulator is empty.
Once the rear wheel antilock is activated, the EBCM
closes the isolation valve. If closing of the isolation
valve is insufficient to prevent wheel lock, the
EBCM
will open the dump valve to allow some rear brake fluid
into the accumulator, thus reducing brake pressure.
The
EBCM will continue to monitor wheel deceleration,
and
if it is still excessive will cause the antilock valve to
dump fluid to the accumulator again. This process will
be repeated until the appropriate wheel speed
correction is calculated by the
EBCM.
When the brake pedal is released, the isolation valve
de-energizes and any fluid in the accumulator is
returned to the master cylinder.
Normal brake operation is resumed.
Fig. 5A3-3

5A3-4 REAR WHEEL ANTILOCK BRAKE SYSTEM
SPEED SENSOR
The speed sensor is single pole, variable reluctance
pick up, mounted
in the rear differential carrier. An
exciter ring
is press fit on the differential ring gear and
provides the signal for the sensor. The
signal generated is proportional
to the average
speed
of the rear wheels and is used by the electronic
brake control module
(EBCM) to determine locking
tendencies
of the rear wheels.
Fig. 5A3-4
•

REAR WHEEL ANTILOCK BRAKE SYSTEM 5A3-5
REAR WHEEL ANTILOCK (RWAL} CONTROL PARTS LOCATION
Fig. 5A3-5
ELECTRONIC BRAKE CONTROL MODULE
The module is located at the front of the center console.
ANTILOCK VALVE (Dual solenoid electrohydraulic)
The valve is located on the front right side of engine room.
SPEED SENSOR/EXCITER RING
The sensor and exciter ring are located on the rear axle carrier.
REAR WHEEL ANTILOCK (RWAL) WARNING LIGHT
The light is located on the instrument panel.
Rear axle
Electronic
brake control module

5A3-6 REAR WHEEL ANTILOCK BRAKE SYSTEM
SYSTEM DIAGRAM
4WD
switch
To 4WD
light -----11~-----lGY 3
Diagnostic Of------0 7 connector
For test
1-----11---+--y 17 Speed
sensor 1-----lt-----L
16
To
stoplight -----,
Stoplight switch
•IJI-----B 15
EBCM Pin View
i
&l ~ IU _, :;) Q
~ _, 0 a: .... z
8 IU ~ c( a: liD (.) z 0 a: 1-(.) IU _, IU
Pressure differential warning switch
(at Combination valve)
r-----+-<1 ~+II•
I•
6 LgB Parking brake _.-MI ____ ___,I'\.JI.Jr-, switch
5
BP -----'
2 w ------------~~._~
GR
4 BrR
9 BrY
20A Fuse F-9
RWAL 10
A •
1• h Fuse C-10
warnmg IQ t (Instrument
Antilock valve panel)
Isolation
valve
~ 4il .J o--1> ~
Reset ~1.5il
I
sw.
Dump valve
(Engine compartment)
13 YG - ACC IG1 Ignition
82 81 switch
50 A
Batt.
10 GW + ,,
15A BOA Fuse C-14 Main (Instrument fuse panel)
RWAL=Rear Wheel Antilock
CONNECTOR View
Fig. 5A3-6
•

5A3-16 REAR WHEEL ANTILOCK BRAKE SYSTEM
CHART E
Rear Wheels Lock with Hard Stops
(Rr. ABS and Brake Lights Self Check Properly)
• APPLY THE BRAKE PEDAL AND CHECK FOR STOP LIGHTS.
STOP LIGHTS WILL NOT ILLUMINATE.
CHECK STOP LIGHT SWITCH OR CIRCUIT, AND REPAIR AS
NECESSARY, AND RECHECK IT.
EXCITER RING IS MISSING, OR TEETH ARE MISSING.
REPLACE
THE EXCITER RING.
VOLTAGE
UNDER 650 mV ON AC SCALE
REPLACE
THE SPEED SENSOR, AND RECHEK SENSOR
OUTPUT.
REAR BRAKES OK.
REPLACE THE EBCM.
STOP LIGHTS OK.
• REMOVE THE SENSOR FROM THE REAR AXLE CASE, AND CHECK FOR MISSING EXCITER RING, OR TEETH MISSING.
EXCITER
RING IS PRESENT, AND TEETH ARE INTACT.
• REINSTALL
THE SENSOR AND RAISE REAR WHEELS TO
SAFELY CLEAR THE FLOOR.
• START ENGINE, AND TURN REAR WHEEL AT 5 MPH.
• REMOVE THE LEFT HAND KICK PANEL, AND USING A
VOLTMETER SET ON THE AC SCALE, CHECK FOR VOLTAGE AT THE TWO PINS OF THE SENSOR TEST
CONNECTOR.
VOLTAGE
OVER 650 mV ON AC SCALE
• REINSTALL
THE KICK PANEL, AND CHECK THE REAR BRAKE FOR MECHANICAL PROBLEMS SUCH AS GRABBING, LOCKING OR PULLING.
REAR BRAKES LOCK, GRAB OR PULL.
REPAIR THE REAR BRAKE PROBLEMS.
EBCM = Electronic Brake Control Module
•

REAR WHEEL ANTILOCK BRAKE SYSTEM 5A3-17
DIAGNOSTIC TROUBLE CODES
FLASHOUT CODES CHART
CONDITION ACTION TO
TAKE
Rr. ABS light flashes 2 times. See Flashout Diagnostic
(High resistance
isolate circuit or malfunctioning EBCM) Trouble Code (DTC) 2
Rr. ABS light flashes 3 times. See Flashout DTC 3
(High resistance
dump circuit or malfunctioning EBCM)
Rr. ABS light flashes 4 times.
See Flashout DTC 4
(Closed rear wheel antilock valve switch)
Rr. ABS light flashes 5 times.
See Flashout DTC 5
System dumps
too many times in 2WD (2WD and 4WD vehicles)
condition
Occurs while making normal or hard stops. Rear brake may lock.
Rr. ABS light flashes 6 times.
See Flashout DTC 6
(Erratic speed sensor reading
while driving)
Rr. ABS light flashes 7 times. See Flashout DTC 7
Isolation output missing or antilock valve wiring shorted to ground
Rr. ABS light flashes 8 times.
See Flashout DTC 8
Dump
output missing or antilock valve wiring shorted to ground
Rr. ABS light flashes 9 times. See Flashout DTC 9
(High sensor resistance)
Rr. ABS light flashes 10 times.
See Flashout DTC 1 0
(Low sensor resistance)
Rr. ABS light flashes 11 times.
See Flashout DTC 11
Stop light switch circuit defective, condition indicated only when driving
above
56 km/h (35 mph)
Rr. ABS light flashes 13 times.
See Flashout DTC 13
(Speed processor check EBCM)
Rr. ABS light flashes 14 times.
See Flashout DTC 14
(Program check
EBCM)
Rr. ABS light flashes 15 times.
See Flashout DTC 15
(Memory failure EBCM)
NOTE:
• Codes 1, 12 and over 15 are not utilized for the diagnostic mode.
EBCM = Electronic Brake Control Module

REAR WHEEL ANTILOCK BRAKE SYSTEM 5A3-25
FLASHOUT DIAGNOSTIC TROUBLE CODE 6
(ERRATIC SPEED SENSOR READING WHILE DRIVING)
(EBCM)
Speed sensor
Test connectors Speed sensor
• DISCONNECT THE BATTERY GROUND CABLE.
• DISCONNECT THE EBCM HARNESS CONNECTOR FROM EBCM, AND
CHECK FOR RESISTANCE BETWEEN HARNESS CONNECTOR PINS, (17
AND 16) WHILE SHAKING THE HARNESS FROM SPEED SENSOR TO EBCM.
EBCM harness connector
Pin (17)
ERRATIC RESISTANCE READING.
REPAIR LOOSE CONNECTION
IN THE SPEED SENSOR
CIRCUITS; CHECK FOR DIRTY OR LOOSE PINS AND FRAYED OR SHORTED CONNECTORS AND RETEST VEHICLE.
METAL CHIPS ARE PRESENT.
DRAIN
AND CLEAN DIFFERENTIAL. CHECK EXCITER RING FOR BROKEN OR CHIPPED TEETH. RETEST VEHICLE.
TEETH ARE DAMAGED, OR LATERAL RUNOUT OF EXCITER
RING IS VISIBLE.
Continued on the next page
CONSTANT READING 1000 TO 2000 OHMS
•
CHECK FOR A BUILD-UP OF METAL CHIPS ON SPEED
SENSOR MAGNETIC POLE PIECE.
NO METAL CHIPS ARE PRESENT.
• ROTATE EXCITER RING,
AND CHECK FOR DAMAGE TO TEETH.
TEETH
ARE INTACT, AND NO VISIBLE LATERAL RUNOUT IS OBSERVED.
Continued on the next page
EBCM
= Electronic Brake Control Module

5A3-26 REAR WHEEL ANTILOCK BRAKE SYSTEM
Continued from the previous page
REPLACE
THE EXCITER RING OF AXLE, AND RETEST
VEHICLE.
REPLACE SPEED SENSOR (THIS FAILURE MAY BE INTERMITTENT DUE TO MOISTURE CONTAMINATION, AND
CANNOT ALWAYS BE DETERMINED BY THE ABOVE RESISTANCE CHECK). Continued
from the previous page
•
REINSTALL SENSOR AND RAISE THE REAR WHEELS TO CLEAR THE FLOOR.
• START THE ENGINE, AND TURN THE WHEELS AT 5 MPH. • USING A VOLTMETER SET ON THE AC SCALE, CHECK FOR VOLTAGE AT THE TWO PINS OF THE SENSOR TEST CONNECTOR.
• RECONNECT BATIERY AND EBCM
CONNECTOR.
• RECONNECT SENSOR HARNESS TO SPEED SENSOR.
• THEN TURN IGNITION ON.
IF DEFECTS STILL EXISTS IN SYSTEM AFTER ALL PREVIOUS
STEPS, REPLACE EBCM.
EBCM
= Electronic Brake Control Module
•