1991 MITSUBISHI 3000GT Service Manual

SERVICE BRAKES -Anti-lock Braking System Troubleshooting35-15
ICheck ABS ECU.Remove the ECU connector and
check.Does the voltage between ECU harness
connector terminal No. 25 and ground
indicate battery voltage while the
ignition key is in the “ON” position?
Yes
b Broken wire between ABS
warning light and ECU) Repair harness.
I ABS ECU malfunctionI) Replace ABS ECU.
Is valve relay normal? (Refer to
P.35-62.)Yes+ Valve relay malfunctionb Replace valve relay.
install the valve relay, remove the HU
connector and check.
IDoes voltage between theINO IHU harness\----+I Broken harness wireII1-1 Repair harness.I
Iconnector terminal No. 8 and ground
indicate battery voltage while the
ignition key is in the “ON” position?between ABS warning
light and HU1IYes
Is there continuity between HU harness
4:~~&?$?%$&ndconnector terminal No. 9 and ground?
Is there continuity between HU harness
connector terminals No. 8 and No.
9?
j HU malfunctionI> Replace HU.
Yes
L Connector not connected
securely., Replace connector.I
TSB Revision

35-16SERVICE BRAKES -Anti-lock Braking System Troubleshooting
BABS warning light stays on when the ignition key is in the “ON” position.
[Explanation]
[Hint]
This is the symptom when the ABS ECU does not
Check the diagnosis output and if there is no output
power up due to broken ECU power circuit, etc.,
voltage or if the MUT and ABS ECU cannot
when the fail safe function operates and isolates thecommunicate, there is a good possibility that power
system or when the warning light drive circuit is
is not flowing to the ECU.
short circuited.
!8IGNIISWIT(-
:Et
J’B @
C151
:
E
COMBINATION
METER
-19
7
------____-_---1
2
610 2
~;@lizEFgIIc,
6227J
r bL-1
IN(IGl)
1
,
ig
)
158
7
r-TSB iCaution
lIf the trouble code is output, the system can
be in the fail safe mode. in such a case, erase
the trouble code and then restart the engine
to check if the system is currently in a fault
condition.
~~~~
~~~~1
I,No ,I
Yes6
Replace ECU.
41,No rIDoes the ABS warning light
remain illuminated even with
the HU connector discon-
nected?
Yes
Short-circuit in harness
between HU or ECU and ABS
warning light
> Repair harness or replace
combination meter.
bvision

SERVICE BRAKES -Anti-lock Braking System Troubleshooting3547CONTINUED FROM
PREVIOUS PAGE
ABS
POSER
RELAY
DIODE
SELF-LM&OS'S
CONNECTOR
FRONT
SIDEYes
Is power relay normal?
(Refer to
P.35-62.)
-Replace power relay.
With the ignition key in the
“ON” position, does voltage
between ECU connector
terminal No. 18 and ground
indicate the battery voltage?
I
1YesNo
-
I--Harness wire between
power relay and ECU
is brokenJ1Repair harness.
I
~ No
Is there continuity betweenrbody harness connector ter-agnosis inspection ter-
minals No. 23 and No. 24,minal and ABS ECU is
and diagnosis inspection ter-
minals No. 4 & No. 1 O?Yes
”Malfunction of ABS ECUReplace ABS ECU.
TSB Revision

35-18SERVICE BRAKES -Anti-lock Braking System Troubleshooting
CABS warning light does not illuminate when the ignition key is in the “START” position.
[Explanation]
LJThe ABS ECU uses the
IG2 power source which is
turned off in the “START” position. The ABS
warning light uses the
IG, 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.
J’B 6
[15
Pi9
I58
:127r',L
ALI
Y-3>
B -
::9
IG-R l,,l G-6
7
COMBINATION
METER
.- ------ ---_-__1
‘$2 1274
7
sE,
85
ON(IGl)
1
;ABS
ECU
H
(--)With the ignition key in the
indicate the battery voltage?
Yes
Yes
I
Yes*Replace valve relay.
HU harness malfunction
NOTEWhen performing the check marked *, note polarity of the diode
(refer to the circuit diagram).
vision

SERVICE BRAKES -Anti-lock Braking System Troubleshooting35-19
DABS warning light blinks once after the ignition key is turned to the “ON” position. It
(L.-Jilluminates in the “START” position and blinks once again when turned to the “ON” position.
[Explanation]
When power flows, the ABS ECU turns on theharness between the ECU and the warning light, the
warning 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.
IGNITIONSWITCH(IG1)
I
COMBINATION
METER
58
g:"I 2
3
mi
456788 7
ASS-ECUIn the ignition key “ON”
position, does voltage
between terminal No. 25 andground indicate battery
voltage?ABS warning light andECUis broken.
Yes
Repair harness.
vMalfunction of ABS ECU
+ Replace ABS ECU.
TSB Revision

35-20SERVICE BRAKES -Anti-lock Braking System Troubleshooting
the following diagnosis codes are displayed “11 FR SNSR. OPEN”
“12 FL SNSR. OPEN” “13 RR SNSR. OPEN” “14 RL SNSR. OPEN”
[Explanation]
The ABS ECU detects breaks in the wheel speed
sensor wire. This trouble code is output if the wheel
speed sensor signal is not input (or short circuited)
or if its output is low when starting to drive or while
driving.[Hint]
In addition to a broken wire/short circuit in the wheel
speed sensor, also check whether the sensor gap is
too large, sensor harness wire is broken, or sensor
harness and body connector are not properly
con-
netted.
r--~- -E-2 When dlagnosls code“15 VEH. SPD. SNSR.” is displayedI[Explanation]
This trouble code is output when there is an
abnormality (other than broken wire or short circuit)
in any of the wheel speed sensor output signals
while driving.
[Hint]
The following can be considered as the cause of the
wheel 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 signal
lSensor output signal is below the standard value
or amplitude modulation is over the standard
value. Using an oscilloscope to measure the
wave shape of the wheel speed sensor output
signal is very effective.l Broken sensor harness
l Poor connection of connector
NOTE(1) If contact is poor, check the sensor cable by
bending and lightly stretching it.
(2) Except for the case where a fault condition
exists in the system, but the inspection results
are normal; if an abnormality cannot be found in
the sensor circuit displayed as abnormal, erase
the diagnosis code and turn the ignition switch
to OFF once, and then test-drive again.
If the same trouble code is output, replace the
ABS ECU. If the trouble does not occur
any-more, the problem is likely to be with the ABS
ECU.(If the trouble is in the speed sensor circuit, but
is difficult to recreate, it will recur even after the
ABS ECU has been replaced.)
SPEED SENSOR
FRONTCLH) FRONTFTRH)RF.AR(LH) REfIR(RH)
@cTJ @ij@ fi&
1 TSB Revision

SERVICE BRAKES -Anti-lock Braking System Troubleshooting35-21
Check flow connected with wheelNOTEspeed sensorWhen checking with an oscilloscope, first measure voltage
iivariations in the wheel speed sensor output. (Refer to P.35-57.)
No
Is the resistance value of the wheel
speed sensor part normal?
Standard value:Front 1.4 - 2.2 kRRear 1.3 - 2.1 kSZ
> Malfunction of wheel speed
sensor
Yes
Yes
1
IIs the standard value for
the gap between the wheel
speed sensor and rotor
within the range?
Standard value:;+;;fi3 - 0.9 mm LO12 -
poe288r,$ - 0.7 mm LOO8 -
Yes
I Yes
ICheck the output of each
wheel speed sensor with an
oscilloscope, including the
waveform. (Refer to mea-
surement of wheel speed
sensor output voltage
variations on
P.35-57.)Is the output voltage for
each wheel speed sensor
over the standard value and
is the waveform normal?
:
No-
Lsensor has a poor wave-
form. Replace sensor or
Yes
RB RevisionI

35-22SERVICE BRAKES -Anti-lock Braking System Troubleshootin,g
E-3When diagnosis code “22 STOP LAMP SW” is displayed
[Explanation]
The ABS ECU outputs this trouble code in the
following cases.
lStop light switch may remain on for more than
15 minutes without ABS operation.
lThe harness wire for the stop light switch may
be open.[Hint]
!LiIf the stop light operates normal, the harness for the
stop light switch input circuit is broken or there is a
malfunction in the ABS ECU.
r7
ABS-ECU-~
RESISTOR
Ll121314/5161716~9~10111~12~13~14/15(16i~7~1~~'9~20~1~2~2~24~~6~~~~9~30~3~~~~2~~5~
KK35-AK-R3506A
I
Yes6
Repair harness.
Malfunction of ABS ECUReplace ABS ECU.
‘visionI