1991 MITSUBISHI 3000GT Service Manual

CRUISE CONTROL SYSTEM - SDecialTools / Troubleshootina13-159
SPECIAL TOOLS
ToolNumber
Name1 Use
MB991341Multi-use testerassemblyl Checking of the self-diagnosis output
MB991 359
ROM pack
TROUBLESHOOTINGMlSEBDWPRELIMINARY INSPECTION
Check the following points and repair defective points, if any, before troubleshooting.
(I) Check that the vacuum pump assembly, link assembly, actuator and all cables and vacuum hoses are
properly installed and that the cables and vacuum hoses are correctly routed.
(2) Check that the link assembly and all cables move smoothly.
(3). Check each of the cables for excessive play or tension.
TROUBLESHOOTING QUICK REFERENCE CHART
Cruise control system is canceled when
cancellation not wanted.
Or, the cruise control system cannot be set after
an automatic cancellation.

Based on the diagnosis output code, check thecircuit and individual parts. (Refer to P.13-173.)
Can cruise control be set at the present moment?- Refer to section on trouble symptoms, “Cruisecontrol cannot be set.” (Refer to P. 13-l 60.)
Does the same problem occur again?
No
Check the diagnosis output. (Refer to P.13-176.)
> AUTO CANCEL activated during operation on asteep slope, or a temporary loose contact in theconnector
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13-160CRUISE CONTROL SYSTEM - Troubleshooting
NOTECruise control system cannot be set.This chart contains troubleshooting procedures to
perform when a problem cannot be detected by
self diagnosis.
Check input. (Refer to P. 13-l 73.)
I
Yes
Is the result of input check O.K.?
!
b Check vacuum pump assembly circuit.(Refer to P. 13-l 67.)
NoNOTEIf the results of checks on the vacuum pumpassemblv circuit and actuator parts (refer to P.13-184.)indicate that they are good, replace the control unit
pen
circurt In contraeplace controlswitch
Defective clutch switchReplace clutch switch
Even when select lever isplacedin
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CRUISE CONTROL SYSTEM - Troubleshootina13461
Trouble symptom
l The set vehicle speed variesgreatly upward or downward.l “Hunching” (repeated alter-
nating acceleration and
deceleration) occurs after
setting is made.
Probable cause
Check chart No.Remedy
Malfunction of the vehicleNo. 4Repair the vehicle speedspeed sensor circuit
sensor system, or replacethe part.Malfunction of thespeedometer cable orspeedometer drive gear
Vacuum pump assembly
No. 5Repair the actuatorcircuit poor contact
system, or replace thepart.Malfunction of thevacuum pump assembly
(including air leaks from
negative pressure
passage)
The cruise control system is notcanceled when the brake pedal
is depressed.Malfunction of the ECU
-Replace the ECU.
Brake switch (for cruiseNo. 6Repair the harness or
control) malfunction
replace the stop light
(short-circuit)switch.
Vacuum pump assemblyNo. 5Repair the harness ordrive circuit short-circuitreplace the vacuum pump
assembly.
The cruise control system is notcanceled when the clutch pedalis depressed. (It is canceled, however, whenthe brake pedal is depressed.)Malfunction of the ECU
-Replace the ECU.
Damaged or disconnected
If the input checkRepair the harness, orwiring of clutch switchcode No. 26 indicatesrepair or replace the clutch
input circuita malfunction.switch.No. 7Clutch switch improper
installation (won’t switch
ON)
Malfunction of the ECU-Replace the ECU.
The cruise control system is notDamaged or disconnectedIf the input checkRepair the harness, or
canceled when the shift lever iswiring of inhibitor switchcode No. 26 indicatesrepair or replace themoved to the “N” position.
input circuita malfunction.inhibitor switch.
(It is canceled, however, when
No. 8
the brake pedal is depressed.)Improper adjustment of
inhibitor switch
Cannot decelerate by using the
SET switch.Malfunction of the ECU
Temporary damaged ordisconnected wiring of
control switch input
circuit
-
No. 2Replace the ECU.
Repair the harness orreplace the control switch
Vacuum pump assemblyNo. 5Repair the harness orcircuit poor contactreplace the vacuum puml:assembly.
Malfunction of thevacuum pump assembly
Malfunction of the ECU
-Replace the ECU.
NOTEECU: Electronic control unit
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13-162CRUISE CONTROL SYSTEM - Troubleshooting
Trouble symptomProbable causeCheck chart No.
Remedy
Cannot accelerate or resume speedOpen or short circuit in
No. 2by using the RESUME switch.RESUME switch circuit inReplace the control switch
control switch
Vacuum pump assemblyNo. 5circuit poor contactRepair the harness or
replace the vacuum pump
Malfunction of thevacuum pump assembly
(including air leaks
from negative pressurepassage)assembly.
Malfunction of the ECU-Replace the ECU.
Even when CANCEL switch is set toON, cruise control is not canceled
Open or short circuit
in CANCEL switchIf the input check
Replace the control switch
(Cruise control, however, iscode No. 27 indicatescircuit in control switch
canceled when brake pedal isa malfunction.
depressed.)No. 2
Malfunction of the ECU-Replace the ECU
The cruise control system can be set
Malfunction of theNo. 4while traveling at a vehicle speedvehicle-speed sensorRepair the vehicle speed
of less than 40 km/h (25 mph), or
circuitsensor system, or replace
there is no automatic cancellationthe part.
at that speed.Malfunction of thespeedometer cable orthe speedometer drive
gear
Malfunction of the ECU
-Replace the ECU.
The cruise control indicator light
No. 3
of the combination meter does notDamaged or disconnectedbulb of indicator lightRepair the harness or
illuminate. (But cruise controlreplace the light bulb.
system is normal)Harness damaged or
disconnected
Malfunction of the ECU
-Replace the ECU.
Cruise control ON indicator light
No. 3
does not come on. (However, cruiseBurned-out indicator lightbulbRepair the harness or
control is functional.)replace the main switch.
Open or short circuit in
harness
Malfunction of control functionby
ON/OFF switching of ELC 4 AA
accelerator switch.
(Non-operation of damper clutch,
2nd gear hold, etc.)
Overdrive is not canceled during
fixed speed driving
No shift to overdrive during
manual driving.
Malfunction of circuitrelated to acceleratorswitch OFF function
Malfunction of the ECU
Malfunction of circuit
related to overdrive
cancellation, or mal-
function of ECU
No. IO
No. 11Repair the harness or
replace the part.
Repair the harness or
replace the part.
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CRUISE CONTROL SYSTEM - Troubleshooting13-163CHECK CHART
it l/Inspection of control unit power supply circuit
L;
,/
id
CRUISE#fi$ROL
0
SWITCH
“71
TROUBLESHOOTING HINTSECU terminal voltage
DESCRIPTION OF OPERATIONThe power is supplied through the ignition switch
(IG,) and cruise control main switch to the control
unit.
1. When the cruise control main switch is set to
ON with the ignition switch at ON, the current
from switch
S, flows through relay Ry, in the
switch. Accordingly, the contact of relay
Ry, is
closed and the power is supplied to the control
unit.
2. When the main switch is released, it automati-
cally returns to the neutral position. Since the
current from switch
S2 flows to relay Ry,, the
contact of relay Ry, remains closed.
3.When the main switch is set to OFF, current to
relay
Ry, is interrupted. This opens the contact
of relay
Ry, to stop the power supply to the
control unit. When the switch is released, it
automatically returns to the neutral position, but
relay Ry, stays in the OFF state.
4. When the ignition switch is set to OFF while
relay Ry, in the main switch is ON, relay
Ry, is
forced to the OFF state just like when the main
switch is set to OFF. Even if the ignition switch
is set to ON again, relay
Ry, stays in the OFF
state until the main switch is set to ON.
NOTEThe numbers beside each connector correspond
to those in the section
(P.13-176) “HARNESS
AND COMPONENTS LAYOUT”
TerminalNo.Signal nameCondition
I
TerminalvoltageI
2Control unit power supplyMain switch ON and neutral positionSystem voltage
thereafter
Main switch OFF and neutral positionov
thereafter8, 14
Control unit groundAt all timesov
16Control unit back up power supplyAt all timesSystem voltage
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13-164CRUISE CONTROL SYSTEM - Troubleshooting
2Inspection of control switch circuit
IGNITIONSWITCHtACC)
*X35-AK-R1302r-
._--------
LE- @CONTROL UNIT
TROUBLESHOOTING HINTSECU terminal voltage
DESCRIPTION OF OPERATIONdThe control switch is a switch in which the SET,
RESUME and CANCEL switches are integrated.
Therefore, different resistance values are used for
the individual switches to change the outputs
(voltages) to the control unit. Current flows through
fuse No. @ of J/B and through the control switch to
the control unit.
1. SET switchWhen the cruise control switch is ON, if the SET
switch is set to ON while vehicle speed is within
a range from about 40 to 145 km/h (25 to 90
mph), the vehicle starts cruising at the speed. If
the SET switch is kept at ON during cruise
operation, the vehicle coasts, and starts cruising
at the speed reached when the SET switch is
set to OFF.
2. RESUME switch
Even if cruise operation is canceled, the vehicle
resumes cruising at the speed set before the
cancellation. Both when the main switch is set
to OFF and when the vehicle speed is reduced
to less than 40 km/h (25 mph) , the vehicle will
not resume cruising at the previously set speed
even if the RESUME switch is set to ON. If the
RESUME switch is kept at ON during cruise
LJoperation, the engine accelerates, and the vehi-
cle starts cruising at the speed reached when
the RESUME switch was set to OFF. (However,
when the vehicle speed is raised to more than
145 km/h (90 mph), the vehicle cruises at
approximately 145 km/h {90 mph).
3. CANCEL switch
When the CANCEL switch is set to ON during
cruise operation, the cancel signal is input to the
control unit which internally interrupts the power
supply to the vacuum pump assembly for
cancellation of cruise operation.
18Control switchSignal name
L
Condition
I
Terminalvoltage1
When all switches are OFFIov1
When SET switch is ONI3vI
When RESUME switch is ON
When CANCEL switch is ON6Vd
Systemvoltage
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CRUISE CONTROL SYSTEM - Troubleshooting13-165
I I3Inspection of indicator light circuitI
CRUl
MAIN-!;$ROLIGNITIONSWITCH(IG1)
l-
CRUISE
CONTROL UNIT
Trl
b!XXSS-AK-RI303
DESCRIPTION OF OPERATION1. Cruise control ON (ASC ON) indicator light
Located in the combination meter, it lights as soon as the main switch is set to ON.
2. Cruise control (CRUISE) indicator light
During cruise control operation, transistor
Tr, in the control unit is kept in the ON state to keep the
indicator light on.
TROUBLESHOOTING HINTSECU terminal voltage
TerminalNo.Signal nameCondition
I
Terminal
voltage
I
23
I I
fr;se control (CRUISE) indicatorWhen cruise control is activeSystem voltage
When cruise control is inactiveov
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13466CRUISE CONTROL SYSTEM - Troubleshooting
I I4Inspection of vehicle speed sensor circuitI

IGNITIONSWITCH(IG1)
5”
El
CRUISE
CONTROL
3UNIT
cl!AI
g6pl!Ezq@zla
;i
d
“m ;ygmq%q
?
VEHICLE
SPEED
SENSOR
xX35-AR-RI304P
19Y
*
$
&
~E$iJ
0z
L
COMBINATION
METER
KX35-AK-Rl3Yla
DESCRIPTION OF OPERATION
The vehicle speed sensor, mounted in the transmission, delivers pulse signals proportional to the rotational
speed of the transmission output gear (vehicle speed) to the control unit. (Four pulse signals generated per
rotation of the output gear) Since the vehicle speed sensor is of the electronic type, the power is supplied
through the ignition switch (IG,).
The vehicle speed sensor is a reed switch type and is mounted in the speedometer. It sends pulse signals
proportional to the rotational speed of the transmission output gear (vehicle speed) to the control unit. (Four
pulse signals generated per rotation of the output gear)
TROUBLESHOOTING HINTSDiagnosis No. 12 (Automatically canceled)
ECU terminal voltage
1TerminalNo.I19
i
Signal nameCondition
Terminalvoltage
Vehicle speed sensor
Slowly drive forward with SELECT lever0 to
0.6Vat “D” or "1 st Speed”2J &l;;:neg
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