ECU MITSUBISHI ECLIPSE 1991 Owner's Guide

5-14BRAKES - Anti-lock Braking System Troubleshooting
aCheck ABS ECU.
Does the voltage between ECU harness
Not Broken wire between ABSRepair harness.connector terminal No.25 and groundwarning light and ECU
indicate battery voltage?
Yes
Replace ABS ECU.Check ABS valve relay.
I

Is valve relay normReplace valve relay.I
YesInstall the valve relay and, with the
(gnition key in the “ON” position>remove the HU connector and check.
IDoes voltage between the HU harnessNow Broken harness wire be-connetor terminal No.8 and ground
indi-tween ABS warning light
cate battery voltage?and HU
Yes
7II1/---I Repair harness.
Is there continuity between HU harnessNo* Broken harness wire be-Repair harness.connector terminal No.9 and ground?tween HU and groundI
YesHU malfunction
Replace HU.

BRAKES - Anti-lock Braking System Troubleshooting5-15
--
BABS warning light illuminated after the engine is started and remains on.
[Explanation]
This is the symptom when the ABS ECU does not
power up due to broken ECU power circuit, etc.,
when the fail safe function operates and isolates thesystem or when the warning light drive circuit is
short circuited.
MAINIGNITION
FUSIBLELINK
@IEYCH
z
A:7
J/B
rb
0
10A
I
:c
r
I
1vAI23
f
! 127ABS ECUCheck, using check chart
E-l -E-6.Check warning light drive
circuit.
t
Does the ABS warning lightNoShort in ECU transistor
remainilluminated even
with the ECU connector dis-
connected?
I
1 YesIReplace
I
Does the ABS warning light
remainilluminated even
with the ECU connector dis-
connected?
Yes
IReplace HU or replacevalve relay.I

5-16BRAKES - Anti-lock Braking System Troubleshooting
SUB
IGNITION
FUSIBLE
SWITCHLINK
@W.2)
I I18
ABS ECU9
SELF-DIAGNOSISCHECKCONNECTOR
No - Correct cause of blown
fuse and replace fuse.
YesWith the ignition key in the
“ON” position,
does ,thf
E;;;; relay make a click
’ Yes ’Disconnect ECU connector
and check harness
connec-
tor.
YesWith the ignition key in the
“ON” position, does voltage
between ECU connector ter-
minal No. 18 and ground in-
dicate the battery voltage?
---j-z-
III
I -11 Repair harness.I
YesMalfunction of ABS ECU
Replace ABS ECU.

BRAKES - Anti-lock Braking System Troubleshooting5-17
CABS warning light does not illuminate when ignition key is in “START” position.
-.[Explanation]
The ABS ECU uses the
IG2 power source which is
turned off in the “START” position. The ABS
warning light uses the
IGI power source which is
not turned off even in the “START” position.
Consequently, in the “START” position, power is offand the ECU turns the valve relay OFF. If the
warning light does not illuminate at this time, there
is trouble in the warning light circuit on the valve
relay side.
MAINIGNITIONFUSIBLESWITCHLINK @(iG1)I
J/B58
15
ABS ECUWith the ignition key in the
“ON” position, does voltagebetween body connector
terminal
No.8 and groundindicate the battery voltage?
Yes

5-18BRAKES - Anti-lock Braking System Troubleshooting
DABS warning light blinks once after the ignition key is turned to the “ON” position. It
illuminates in the “START” position and blinks once again when turned to the “ON” position.
[Explanation]
When power flows, the ABS ECU turns on the
harness between the ECU and the warning light, thewarning light for approximately 1 sec. while itlight illuminates only when the valve relay is off in
performs a valve relay test. If there is a break in thethe valve relay test, etc.
125
El
ABS ECU
14A0597connector and check with
I
In the ignition key “ON”
_ No ~ Harness wire between
position, does voltage
be-ABS warning light and
tween terminal No.25 andECU is broken.
ground indicate battery vol-
tage?
YesRepair harness.
tMalfunction of ABS ECU
Replace ABS ECU.

BRAKES - Anti-lock Braking System Troubleshooting549
E-lInput abnormality of wheel speed sensorI-[Explanation][Hint]The ABS ECU detects breaks in the wheel speed
In addition to a broken wire/short circuit in the wheelsensor wire. The warning light lights up if the wheel
speed sensor, also check whether the sensor gap isspeed sensor signal is not input (or short circuited)
too large, rotor teeth are missing, sensor harness
or if its output is low when starting to drive or while
wire is temporarily broken, or sensor harness and
driving.body connector are not properly inserted.
I IE-2Output abnormality of wheel speed sensorI
[Explanation]The warning light lights up when there is an
abnormality (other than broken wire or short circuit)
in the wheel speed sensor output signal while
driving.
[Hint]
The following can be considered as the cause of thewheel speed sensor output abnormality.
l Distortion of rotor, teeth missing
lLow frequency noise interference when sensor
harness wire is broken
l Noise interference in sensor signall When the sensor output signal is below the
standard value or when amplitude modulation is
over the standard value, using an oscilloscope tomeasure the wave shape of the wheel speed
sensor output signal is very effective.
l Loose wheel bearing
l Temporarily broken wire in sensor harness
l Sensor harness and body connector are not
properly inserted.
NOTE
If contact is poor, check the sensor cable by bendingand lightly stretching it.
SPEED SENSOR
FRONTREAR(LEFT SIDE) (RIGHT SIDE) (LEFT SIDE) (RIGHT SIDE)
Km
I-.IIGND
III24I
FRONT SIDE
I
ABSECU
REVERSE SIDE
SELF-DIAGNOSIS
CHECK CONNECTOR
14AO601

5-20 _BRAKES - Anti-lock Braking System TroubleshootingCheck flow connected with wheel speed
sensorNOTE:When checking with an oscilloscope, first measure voltage
variations in the wheel speed sensor output. (Refer to
P.5-51.)
Is the resistance value of the wheelNo c Malfunction of wheel speedReplace wheel speed
speed sensor part, which the displayedsensor
sensor.trouble code indicates, normal?
Standard value:
0.8-l .2 kQ
I YesIs the resistance value with the ECU
No c Harness wire for wheel -Repair harness.connector normal?
speed
sensorcircuit is
Ibroken.
II1
1
Is the standard value for the
gap between the wheel
speed sensor and rotor,
which the output trouble
code indicates, within the
range?
Standard value:
h
%Z~Pf!;!~~~e~no missing or damaged
teeth?
1 Yes
1Check the output of each
wheel speed sensor with an
oscilloscope, including the
waveform. (Refer to
measurement ofwheel
speed sensor output voltage
variations on
P.5-51 .I Is the
output voltage for each
wheel speed sensor over
the standard value and is thewave form normal?
Yes
Canthe abnormality beNoRepair harness.foundeven if the sensorIharness and connection be-
tween sensor harness and
body harness are bent and
estretched?
Yes

BRAKES - Anti-lock Braking System Troubleshooting5-g
E-3Abnormality of stop light switch circuit
_ [Explanation][Hint]The ABS ECU turns on the warning light in theIf the stop light operates normal, the ABS harness
following cases.
wire for the stop light switch input circuit to the ECUlStop light switch may remain on for more than
is broken or there is a malfunction in the ABS ECU.15 minutes without the ABS functions.
lThe harness wire for the stop light switch may
be open.
T AUTO-
TOPIGHT
WITCH
ABSECUDo the stop lights light up
Noand go out normally?c Check the stop light re-lated circuit and repair
Iproblem spots.
the ABS
ECUconnector and inspect at
>the harness side connec-
L No
When the brake pedal is
pressed
forcefullv, does thevoltage between’ connector
terminal No. 29 and ground
indicate battery voltage?Harness wire between
* stop light switch and ABS
ECU is broken.
J1 Repair harness.I
Yes
IStop light switch circuit isnormal.l

5-22BRAKES - Anti-lock Braking System Troubleshooting
1 E-4 1 Abnormality of solenoid valve drive circuit
[Explanation]
The ABS ECU normally monitors the solenoid valve
drive circuit.
If no current flows in the solenoid even if the ECU
when turned OFF, the ECU determines the solenoidcoil wire is broken/short circuited or the harness
isbroken short circuited and then warning light lights
turns the solenoid ON or if it continues to flow even
up.
J/B
HU
(
x:OMBINATION ME
:TER
MA0603
Is the resistance value for
the solenoid valve, that the
displayed trouble code indi-cates, within the range of
the standard values?
Standard value: 3.0-3.2 Q
Is the solenoid valve resist-
ance value, that the output
trouble code displays, withinthe range of the standard
values when measured at
the ECU connector?
Standard value: 3.0-3.2 B
nOrmll/
Solenoid valve drive circuit is
NoReplace HU.I
NoThe harness wire for thesolenoid valvecircuit
whose resistance value is
outside the range of the
standard value is broken
or short circuited.
I
1 Repair ABS harness.

BRAKES - Anti-lock Braking System Troubleshooting5-23
E-5Abnormality of valve relay drive circuit
~- [Explanation]Ii ;.
\jVhen the ignition switch is turned ON, the ABSnormal. In addition, normally it monitors whether qrECU switches the valve relay OFF and ON for annot there is power in the valve power monitor line
initial check, compares the voltage of the signal tosince the valve relay is normally ON. Then, if the
the valve relay and valve power monitor line voltagesupply of power to the valve power monitor,line is
tocheck whether the valve relay operation isinterrupted, the warning light illuminates.
IGNITIONMiN&USIBLESWITCH(IGI)
ECU
1When the valve relay is
checked, are the following
conditions found?Valve relay malfunction
I
No. 85-No. 86:resistancevalue 60-120 QNo. 30-No. 87a: continuity
No. 30-No. 87: No continui-
tYWhen battery voltage is ap-
plied between terminals
No. 86 and No. 85 grounded.No.
30-No. 87: continuity
No. 30-No. 87a: no continui-
Install the valve relay and
remove the HU connec-
t the HU harnesandremove the ECU con-Is there continuity between
body connector terminal No.
22 and ground?
Yes
Valve relay drive circuit is
normal.