1991 MITSUBISHI 3000GT Service Manual

SERVICE BRAKES -Anti-lock Braking System Troubleshooting35-7
ANTI-LOCK BRAKING SYSTEM TROUBLESHOOTlilGPARTICULAR PHENOMENA OF THE
LANTI-LOCK BRAKING SYSTEMModels equipped with the anti-lock braking system
(ABS) may exhibit one or more of the following
phenomena from time to time, but none of these
are abnormal.
(1) A pulsing feeling in the brake pedal, or vibration
of the body or the steering wheel, when the
anti-lock braking system is activated by sudden
braking or by braking on a slippery road surface.
.9ctually, this phenomenon is an indication that
the anti-lock braking system is functioning nor-
mally.(2) When the vehicle speed reaches approximately
6 km/h (4 mph) after the engine is started and
the vehicle starts off (for the first time), a
whining motor noise may be heard from the
engine compartment if the vehicle is traveling in
a quiet place, but this noise is simply the result
of a self-check being made of the anti-lock
braking system operation.
TROUBLESHOOTING METHODSProblems related to the anti-lock braking system
(ABS) can be classified into two general categories:
problems in the electrical system and those in the
Lhydraulic system.For problems in the electrical system, the
self-diagnosis function is built into the electronic control
unit (E.C.U.) causing the ABS warning light to
illuminate as a warning to the driver. In this instance,
checks can be made by using the multi-use tester
and oscilloscope.
Problems in the hydraulic system (poor braking,
etc.) can be located in the same way as for ordinary
brakes. There is, however, the necessity to check to
determine whether the problem is related to ordin-
ary brake components or to the components related
to the ABS. To make this check, use the multi-use
tester.
HOW TO USE THE TROUBLESHOOTING
FLOW CHART(1) Using the flow chart, check the ABS warning
light light-up sequence. Read the diagnosis
codes and check the condition of braking opera-
tion.
(2) Following the check chart listed in the remedy
column, perform the checks. There are [Explana-
tion] and [Hint] in each check chart. Refer to
them when troubleshooting.
NOTEECU: Electronic control unit
HU: Hydraulic unit
MUT: Multi-use tester
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35-8SERVICE BRAKES -Anti-lock Braking System Troubleshooting
TROUBLESHOOTING (ABS - FWD)Confirm condition in the following way and diagnosis accordingly.
Does the ABS warning light illuminate as described
(2) With the ignition key in the “START” position,
below up to the time the engine starts?power to the ABS ECU is interrupted and the
(1) When the ignition key is turned to the “ON”ABS warning light remains lit because the valve
position, the ABS ECU causes the ABS warningrelay is OFF.
light to flash twice in about one second (during
(3) When the ignition key is returned from the
which the valve relay self check is made) and“START” position to the “ON” position, the
then causes it to go out.ABS warning light flashes twice in about one
second (during which. the valve relay self check
-is made again) and then goes out.
ABS warning
ONlightII
-I
keyACC,
LO!: +--14A0589
Yes>CONTINUED ON NEXT PAGE
No
”
weenABS warning
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SERVICE BRAKES -Anti-lock Braking System Troubleshooting
L’
No.Trouble condition\4
After the ignition key is turned to the
“ON” position, it blinks once and then
illuminates when it is turned to the
“START” position. When the key is
returned to the “ON” position, the light
blinks again. (Blinking with the ignition
key in the “ON” position is synchronized
with operation noise of the valve relay.)
ABSwarninglight
key ACC. L::+
Ignition
14A05931 CONTINUED FROM PREVIOUS PAGE
1Major causes
l Break in harness for ECU warning
light drive circuit
l Malfunction of ECU
Does the ABS warning light illuminate
when starting to drive the car?
iIs there one-sided braking, insufficient
>CONTINUED ON NEXT PAGEI
I
YesTrouble condition
One-sided braking
Insufficient braking force
ABS sometimes functions even when
there is no sudden braking.
(ABSoperation vibration is transmitted.)Remedy
Check, using flow
P.35-19.)Remedy
l Check HU operation and, if
l necessary, replace HU.
If HU is normal, check struc-
l
HydraJicl Malfunction in HU solenoid valvetural parts for normal
braking.
Insufficient wheel speed sensor put voltage (sensor malfunction, too
large a gap between sensor rotor,
l Malfunction of ABS ECU(Refer to
P.35-57.) and, if
necessary, replace sensor,
If tests indicate that there are
no mechanical or electricalfaiIures,replace the ECU.
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35-10SERVICE BRAKES -Anti-lock Braking System Troubleshooting
j CONTINUED FROM PREVIOUS PAGE /After a test drive, use self-diagnosis to
P.35-11.).>
1No trouble codes output and normal
codes are displayed?
NoTrouble codes are output
Yes
All ABS functions are normal.
(Nor are there stored memory of
past trouble code.)put terminals and the di-
agnosis check connector.
If trouble does not re-
appear, watch vehicle
movements until it reap-
pears. (Refer to
P.35-12.)
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SERVICE BRAKES -Anti-lock Braking System Troubleshooting
35-11
Adapter
iarness%f&(MB9913771(Mi3991341)\12FOO57
CHECK USING SELF DIAGNOSIS FUNCTION
(1) With the ignition switch OFF, connect the MUT through the
adapter harness
(MB9913771, turn the ignition ON and
select the ABS system. (The ABS warning light lights up, it
goes into the MUT mode. In the MUT mode, ABS does
not function.)
If it does not go into the MUT mode, check the ECU power
circuit and the harness between the ECU and diagnosis
check terminals.
(2) Read the diagnosis output codes from the ECU memory.
(3) Clear the diagnosis codes once from memory. (Refer to
P.35-12.)If the memory cannot be cleared, the ECU is currently
detecting the trouble and the ABS ECU is in fail safe. If it
can be cleared, the trouble is either temporary or appears
only when driving.
(4) When the trouble codes cannot be cleared, or when the
ABS ECU goes into fail safe during another test drive and
trouble codes are output, check according to trouble code
check charts (E-l-E-6).
DIAGNOSIS CODE CHART
Diagnosis codeCheckReferenceDiagnosis codeCheck
Referencechart namepagechart namepawNo. MUT display lettersor remedyNo. MUT display lettersor remedy
L11FR SNSR. OPEN41FR SOL. VALVE
12FL SNSR. OPEN42FL SOL. VALVEE-4P.35-23E-lP.35-2013RR SNSR. OPEN43REAR SOL. V.
14RL SNSR. OPEN51VALVE RELAYE-5P.35-24
15VEH. SPD. SNSR.E-2P.35-20 52MOTOR RELAYE-6P.35-25
22STOP LAMP SWE-3P.35-2055 CONT. UNITECU-
replacementI
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35-12SERVICE BRAKES -Anti-lock Braking System Troubleshooting
METHOD OF CLEARING DIAGNOSIS
ACTUATOR TEST FUNCTION
CODE MEMORYThe actuator can be forcibly driven in the following
Cautionway by using the MUT.
lWhen servicing is finished, clear the diagno-
sis code memory.NOTEd
lThe actuator test cannot be carried out when the
Trouble codes cannot be cleared from memoryABS ECU system is in fail safe.
when the ABS ECU system is in fail safe. Proceed tol When using forced drive using the MUT, the
diagnosis and repair.vehicle must be stopped.
(1) Clear memory using MUT.
lDuring forced drive using the MUT, forced drive
(No. 7
“DIAG. ERASE” in the actuator test isoperation is stopped when any wheel speed
selected to erase the diaanosis code.)reaches 10 km/h (6 mph).
(2) After clearing, recheck the diagnosis codes, and
check that memory is cleared.
Actuator test specifications
No.MUT display
01FR VALVE A
02
FL VALVE A03
REAR VALVE A04
FR VALVE M
05
FL VALVE M06
REAR VALVE MDrive solenoid
valve and motorDrive pattern
Not used
Solenoid valve and
pump motor for
each HU corres-
ponding channel.

Start of forced drive
End of forced drive
1440588
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.SERVICE BRAKES -Anti-lock Braking System Troubleshooting35-13 'A ABS warning light does not light at all.
iJ[Explanation][Hint]
When it does not light up at all, there is a strongIf other warning lights do not light up either, fuse is
possibility that there is trouble with ABS warningprobably blown.
light or with power to the light.
id
r
f%ER RELAY
110
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6
::5
d
.-2=
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2____--..-
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5fir 4
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4 -
IGNITIONSWITCH(IG2)m!--
mj:
JSIBLE LINK0tiB
2
L__---------___
0
Lp1%
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j:(L-R)dg
6-k
&h+&"..L"Ei SOLENOID1:
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G-R
^ -tl- - D
HH H?bb
IN:IGl)-
59
1
ki@iNATION
iB
ABS-ECU
Kxss-AK-RSGOIA
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SERVICE BRAKES- Anti-lock Braking System Troubleshooting
Yes
Turn the ignition switch OFF and
check.
4- No
Does voltage between
harness connector terminal
No. 14 and ground indicate
battery voltage?combination meter from
fuse No. 11 is broken.
Yes
ylCircuit in combination meter
is broken.
Is there continuity between combination
meter No. 58 and No 59 terminals7
.rT/“I./ Faulty1 +I[&
r,No ,IAre instrument panel wiring harness
and body wiring harness connected
properly?Connect connectors firmly.
(Check for pins pulled out or
bent, and repair as needed.)
Yes
Broken wire in ECU, valve relay or both
drive circuits. Check both circuits.
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