1991 MITSUBISHI 3000GT ABS

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(-
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COMBINATION
METER
-19
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------____-_---1
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158
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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.
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COMBINATION
METER
.- ------ ---_-__1
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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

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

SERVICE BRAKES -Anti-lock Braking System Troubleshooting35-23
E-4When diagnosis codes “41 FR SOL. VALVE”, “42 FL SOL. VALVE” or
“43 REAR SOL.
V.” are displayed.
iL[Explanation]
The ABS ECU normally monitors the solenoid valve
when turned OFF, the ECU determines the solenoid
drive circuit.
coil wire is broken/short-circuited or the harness is
If no current flows in the solenoid even if the ECU
broken/short-circuited, and then these trouble
turns the solenoid ON or if it continues to flow even
codes are output.
/
ii
LJ
$$l.E#AT'ON;;QO'D
4I
I
i
Ii'-. - - ---i>? 5 3 6
ABS-ECU-A22 Al9 *17 ,IY Y Y Y I
disconnect ECU connector
Yes
The harness wire for the
solenoid valve circuit
whose resistance value is
outside the range of the
standard value is brokenor short circuited.
I
Repair ABS harness.
Malfunction of ABS ECU
1) Replace ABS ECU.
TSB Revision

35-24SERVICE BRAKES -Anti-lock Braking System Troubleshooting
E-5When diagnosis code “51 VALVE RELAY” is displayed
[Explanation]
When the ignition switch is turned ON, the ABS
ECU switches the valve relay OFF and ON for an
initial check, compares the voltage of the signal to
the valve relay and valve power monitor line voltage
to check whether the valve relay operation isnormal. In addition, normally it monitors whether or
not there is power in the valve power monitor line
since the valve relay is normally ON. Then, if the
supply of power to the valve power monitor line is
interrupted, this trouble code will be output.
EPfiiB EenIGNITIONSWITCH(IG1)
COMSINATIONm
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1/2131a)5161718(QIIO(I ~~~2(13~~a~i5~~6/i7~~~IQ$O~Y~2~3~24~~6~~~28~~~1~2~3~4~5~Remove and check the valve relay.
IWhen the valve relay is checked, are
the following conditions found?
No. 85
-No. 86: Resistance
value 60 - 120 fiNo. 30-No. 87a: Continuity
No. 30 - No. 87: No continuity
When battery voltage is applied
between terminals No. 86 and No. 85.
No. 30
- No. 87: Continuity
No. 30 - No. 87a: No continuity
Yes
Install the valve relay and remove
the HU connector.
E+GG-pqReplace valve relay.
&I/ NnIIWith the ignition key “ON”, does the
Is there continuity between HU No. 8
and No. 7 terminals?
IYes
Connect the HU harness and remove
the ECU connector.Faulty harness in HU
1Does resistance between body con-
nector terminal No. 2 and terminal
No. 27 indicate 60
- 120 II
NoMalfunction of harness
between HU and ECU.
Yes
With the ignition key “ON”, does the
voltage between terminal No. 22 and
ground indicate battery voltage?
YesNo
II- Malfunction of harness
between HU and ABS
ECU.Repair harness.
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