1991 MITSUBISHI MONTERO sensor

95C). Disconnect oxygen sensor connector. See Fig. 5. Connect
ohmmeter between heater terminals of oxygen sensor connector as
specified in OXYGEN SENSOR 4-WIRE CONNECTOR TERMINAL IDENTIFICATION
table. This test checks resistance of oxygen sensor heater element.
Fig. 5: O2 Sensor Connector Term. ID
Courtesy of Mitsubishi Motor Sales of America.
2) When oxygen sensor is at 68
F (20C), resistance should be
approximately 12 ohms (20 ohms on 3.0L models). If resistance is not
within specification, replace oxygen sensor.
CAUTION: DO NOT apply battery voltage to oxygen sensor output
terminals. Damage to oxygen sensor could result.
3) Apply battery voltage to oxygen sensor heater terminals as
specified in OXYGEN SENSOR 4-WIRE CONNECTOR TERMINAL IDENTIFICATION
table. This heats oxygen sensor heater element.
4) Connect digital voltmeter between output terminals
specified in OXYGEN SENSOR 4-WIRE CONNECTOR TERMINAL IDENTIFICATION
table. Repeatedly race engine and observe oxygen sensor output
voltage. If oxygen sensor output voltage is not within 0.6-1.0 volt,
replace oxygen sensor.
OXYGEN SENSOR 4-WIRE CONNECTOR TERMINAL ID TABLE









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Heater Output

Circuit Circuit
Application Terminals Terminals
Montero, Pickup 3.0L & Ram-50 3.0L ..... 2 & 4 ............. 1 & 3









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POWER STEERING OIL PRESSURE SWITCH
1) Power steering oil pressure switch is mounted on power
steering pump. Disconnect single wire connector at switch. Start
engine.
2) Connect ohmmeter between switch terminal and ground. If
continuity is present with steering wheel in straight-ahead position,
replace switch. If continuity is not present while turning steering
wheel, perform POWER STEERING IDLE-UP SYSTEM TEST. See IDLE-UP SYSTEMS
under IDLE CONTROL SYSTEM.
THROTTLE POSITION SENSOR
1) TPS is mounted to throttle body, at end of throttle shaft.
Disconnect TPS connector. See Fig. 6. Using ohmmeter, measure total
resistance between TPS connector terminals as specified in TPS
CONNECTOR TERMINAL IDENTIFICATION table. If resistance is not 3500-
6500 ohms, replace TPS.
2) Using an analog (needle-type) ohmmeter, measure variable
resistance between TPS connector terminals as specified in TPS
CONNECTOR TERMINAL IDENTIFICATION table.
3) Operate throttle valve from closed to wide open throttle.
If rate of resistance does not change smoothly within 3500-6500 ohms
throughout range of throttle valve movement, replace TPS.
Fig. 6: TPS Sensor Connector Terminal ID
Courtesy of Mitsubishi Motor Sales of America.
TPS CONNECTOR TERMINAL IDENTIFICATION TABLE









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Terminal
Application Numbers
Total Resistance .................... 1 & 4
Variable Resistance
Montero, Pickup 3.0L,
& Ram-50 3.0L .................... 1 & 3
All Others ........................ 2 & 4









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VEHICLE SPEED SENSOR
1) Vehicle Speed Sensor (VSS) is located in speedometer
assembly. Connect an ohmmeter between sensor terminals on back of
instrument panel. See Fig. 7 or 8.
2) Rotate speedometer cable. For each revolution of
speedometer cable, sensor should make and break continuity 4 times. If
ohmmeter reading does not fluctuate between continuity and no
continuity or if sensor does not make and break continuity 4 times for
each revolution, replace sensor.
Fig. 7: VSS Sensor Connector Term. ID (Montero)
Courtesy of Mitsubishi Motor Sales of America.
Fig. 8: VSS Sensor Connector Term. ID (P/U & Ram 50)
Courtesy of Mitsubishi Motor Sales of America.
MOTORS, RELAYS & SOLENOIDS

right several times. Start engine, and turn steering wheel back and
forth to raise fluid temperature to approximately 122-140F (50-60C).
3) With engine idling, gradually close shutoff valve of
pressure gauge to increase hydraulic pressure. If idle speed does not
increase 200-250 RPM when fluid pressure reaches 213-284 psi (15-20
kg/cm
), replace power steering idle-up switch.
4) Gradually open shutoff valve. If engine speed does not
return to curb idle speed between 100-142 psi (7-10 kg/cm
), replace
power steering idle-up switch. Remove testing equipment. Bleed air
from system as in step 2).
IGNITION SYSTEM
NOTE: For basic ignition checks, see F - BASIC TESTING article in
ENGINE PERFORMANCE Section.
TIMING CONTROL SYSTEMS
Crank Angle Sensor
Crank angle sensor is located inside distributor on SOHC
engines and is attached to cylinder head on DOHC engines. If
malfunction occurs, Code 22 will set. For testing procedure, see
appropriate G - TESTS W/CODES article in the ENGINE PERFORMANCE
Section.
EMISSION SYSTEMS & SUB-SYSTEMS
EXHAUST GAS RECIRCULATION (EGR)
System Testing (Federal)
1) Disconnect Green-striped hose from throttle body, and
connect vacuum pump to hose end. Plug nipple where hose was connected
to throttle body. When engine is cold, 122
F (50C) or less, and at
idle, apply vacuum to disconnected hose. If idle does not change and
vacuum bleeds down, system is okay.
2) When engine is hot, 205
F (95C), and at idle, apply 1.8
in. Hg. If idle does not change and vacuum holds, system is okay.
Using a vacuum pump, apply 7.7 in. Hg. If idle becomes unstable or
engine stalls (and vacuum holds), system is okay.
System Testing (California)
1) Connect vacuum "T" fitting into Green-striped hose from
EGR valve, and connect vacuum gauge to vacuum tee. When engine coolant
temperature is 68
F (20C) or less and engine is idling, snap throttle
open to race engine. If no change in vacuum reading is detected on
gauge, system is okay.
2) When engine coolant temperature is 158
F (70C) or more
and engine is idling, snap throttle open to race engine. If vacuum
increases to 3.9 in. Hg or higher, system is okay.
3) Using vacuum pump, apply specified vacuum to open EGR
valve. See EGR VALVE SPECIFICATIONS table. If idle becomes unstable or
engine stalls, system is okay.
EGR Control Solenoid Valve (Pickup & Ram-50, California)
1) EGR control solenoid valve is located near left shock
tower. Label and disconnect vacuum hoses and wiring harness from
solenoid valve.
2) Connect hand vacuum pump to vacuum nipple where Green-
striped vacuum hose was connected. Apply vacuum and ensure vacuum does
not hold. Apply battery voltage to one terminal of solenoid, and
ground other. Ensure vacuum holds.

3) Using an ohmmeter, measure resistance between terminals of
solenoid valve. At room temperature, reading should be 36-44 ohms.
Replace solenoid if not to specification.
NOTE: EGR temperature sensor only determines if EGR is operating.
An inoperative sensor will not affect driveability or
exhaust emissions.
EGR Temperature Sensor (California)
1) Remove EGR temperature sensor from EGR valve. Place EGR
temperature sensor in water. While increasing water temperature,
measure resistance between wire terminals.
2) At a temperature of 122
F (50C), resistance should be 60,
000-80,000 ohms. At 212F (100C), resistance should be 11,000-14,000
ohms. Replace EGR temperature sensor if resistance differs
significantly from specifications.
EGR Valve
1) Remove EGR valve. Check valve for sticking, carbon
deposits and damage. Clean valve with solvent if necessary. Apply 19.8
in. Hg to valve diaphragm. If valve does not hold vacuum, replace
valve.
2) Apply specified vacuum to valve diaphragm. See CLOSED IN.
HG in EGR VALVE SPECIFICATIONS table. If valve begins to open below
specification, replace valve.
3) Apply specified vacuum to valve diaphragm. See OPEN IN. HG
in EGR VALVE SPECIFICATIONS table. If valve is not completely open at
or above specification, replace valve.
EGR VALVE SPECIFICATIONS TABLE









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Application Closed Open
In. Hg In. Hg
Montero ....................... 2.4 ........... 6.7
Pickup & Ram-50 ............... 1.2 ........... 9.4









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FUEL EVAPORATION
System Test
1) Disconnect Red-striped purge hose from throttle body, and
connect to hand vacuum pump. Plug nipple on throttle body where purge
hose was removed.
2) With engine coolant temperature at 140
F (60C) or less
and engine idling, apply 14.8 in. Hg. Vacuum should hold. Raise engine
speed to 3000 RPM and again apply 14.8 in. Hg. Vacuum should hold.
3) With engine coolant temperature at 158
F (70C) or more
and engine idling, apply 14.8 in. Hg. Vacuum should hold. Turn engine
off. Start engine and within 3 minutes of starting engine, apply
vacuum. Vacuum should bleed down.
4) With engine running for more than 3 minutes after
starting, raise engine speed to 3000 RPM and apply 14.8 in. Hg. Vacuum
should hold momentarily and then bleed down.
NOTE: In step 4), vacuum should bleed down continuously if vehicle
is at an altitude of 7200 ft. (2200 m) or higher or if
intake air temperature is 122
F (50C) or higher.
Purge Control Solenoid Valve
1) Purge control solenoid valve is located near left shock
tower. Label and disconnect both vacuum hoses from solenoid valve.
Disconnect electrical connector. Connect hand vacuum pump to solenoid

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G - T E STS W /C O DES
1991 Mitsubishi Montero
1990-91 ENGINE PERFORMANCE
Chrysler Motors/Mitsubishi Self-Diagnostics
Dodge; Colt, Colt Vista, Colt Wagon
Eagle; Summit
Mitsubishi; Eclipse, Galant, Mirage, Montero, Precis (1990)
Plymouth; Colt, Colt Vista, Colt Wagon
INTRODUCTION
If no faults were found while performing F - BASIC TESTING,
proceed with self-diagnostics. If no fault codes or only pass codes
are present after entering self-diagnostics, proceed to H - TESTS W/O
CODES article for diagnosis by symptom (i.e. ROUGH IDLE, NO START,
etc.).
SELF-DIAGNOSTIC SYSTEM
Use Chrysler Motors code charts when using Chrysler's
Diagnostic Readout Box (DRB-II). If DRB-II is not available or if
working on a Mitsubishi Motors vehicle, system diagnosis can only be
accomplished using a voltmeter or appropriate scan tester. To diagnose
Chrysler Motors and Mitsubishi models using a voltmeter, see
ENTERING ON-BOARD DIAGNOSTICS (USING VOLTMETER) in this article.
SYSTEM DIAGNOSIS
SYSTEM DIAGNOSIS DESCRIPTION
NOTE: Chrysler Motors recommends using DRB-II to diagnose system.
Voltmeter usage has limited diagnostic capabilities but can
be used if DRB-II is not available or if working on a
Mitsubishi Motors vehicle.
The Engine Control Unit (ECU) monitors several different
engine control system circuits. If an abnormal input signal occurs, a
fault code is stored in ECU memory and given a fault code number. Each
circuit has its own fault number and message. A specific fault code
indicates a particular system failure, but it DOES NOT indicate that
cause of failure is necessarily within system. A fault code DOES NOT
condemn any specific component; it simply points out a probable
malfunctioning area. If a critical fault code is set, the ECU will
turn on CHECK ENGINE light. All fault codes except speed sensor are
considered critical.
Fault codes can be confirmed by using a voltmeter on Chrysler
Motors and Mitsubishi models or Chrysler's Diagnostic Readout Box
(DRB-II) on Chrysler Motors vehicles. See
ENTERING ON-BOARD DIAGNOSTICS (USING VOLTMETER) or ENTERING ON-BOARD
DIAGNOSTICS (USING DRB-II) in this article. By using the DRB-II, the
self-diagnostic capabilities of this system can simplify testing and
reduce diagnostic time.
System malfunctions encountered are identified as either hard
failures or intermittent failures as determined by the ECU.
HARD FAILURES
Hard failures cause CHECK ENGINE light to illuminate and
remain on until the malfunction is repaired. If light comes on and

remains on (light may flash) during vehicle operation, cause of
malfunction must be determined by using DIAGNOSTIC FAULT CHARTS (if
testing with voltmeter) or diagnostic CODE CHARTS (if testing with
DRB-II). If a sensor fails, ECU will use a substitute value in its
calculations to continue engine operation. In this condition, vehicle
is functional, but loss of good driveability may result.
INTERMITTENT FAILURES
Intermittent failures may cause CHECK ENGINE light to flicker
or illuminate and go out after the intermittent fault goes away.
However, the corresponding trouble code will be retained in ECU
memory. If related fault does not reoccur within a certain time frame,
related trouble code will be erased from ECU memory. Intermittent
failures may be caused by a sensor, connector or wiring related
problems. See INTERMITTENTS in H - TESTS W/O CODES article.
PRETEST INSPECTION
Before proceeding with diagnosis, the following precautions
must be followed:
* Vehicle must have a fully charged battery and functional
charging system.
* Visually inspect connectors and circuit wiring being worked
on.
* DO NOT disconnect battery or ECU. This will erase any fault
codes stored in ECU.
* DO NOT cause short circuits when performing electrical tests.
This will set additional fault codes, making diagnosis of original
problem more difficult.
* DO NOT use a test light in place of a voltmeter.
* When checking for spark, ensure coil wire is NO more than
1/4" from ground. If coil wire is more than 1/4" from ground,
damage to vehicle electronics and/or ECU may result.
* DO NOT prolong testing of fuel injectors. Engine may
hydrostatically (liquid) lock.
* When a vehicle has multiple fault codes, always repair lowest
number fault code first.
* If DRB-II is being used to diagnose system, always perform
verification test after repairs are made.
ENTERING ON-BOARD DIAGNOSTICS (USING VOLTMETER)
1) Before entering on-board diagnostics, refer to PRETEST
INSPECTION in this article. Turn ignition switch to OFF position.
Locate self-diagnostic connector. See SELF-DIAGNOSTIC TEST CONNECTOR
LOCATION table. Using an analog voltmeter, connect voltmeter positive
lead to self-diagnostic connector terminal No. 1 and negative lead to
terminal No. 12 (ground). See Fig. 6.
2) Turn ignition switch to ON position and disclosure of ECU
memory will begin. If 2 or more systems are non-functional, they are
indicated by order of increasing code number. Indication is made by
12-volt pulses of voltmeter pointer. A constant repetition of short
12-volt pulses indicates system is normal. If system is abnormal,
voltmeter will pulse between zero and 12 volts.
3) Signals will appear on voltmeter as long and short 12-volt
pulses. Long pulses represent tens; short pulses represent ones. For
example 4 long pulses and 3 short pulses indicates Code 43. See

PROCEDURE chart after repairs. Ensure charts apply to engine
being tested.
DRB-II KEY FUNCTIONS
* YES or Down Arrow & NO or Up Arrow
Keys will move lines on screen up or down allowing you to
choose an item or scroll through all selections
available.
* F1 & F2 Keys
Keys are used to scroll through sensor displays.
* ATM Key
Key will return you to previous screen.
* ENTER Key
Allows you to select a test or display. The flashing
arrow must be on the display you wish to select. Pressing
ENTER in the sensor state will cause display to change
from a 3-line display to a 1-line display.
* F3 Key
Key is used to display a help screen. This key may be
used at any time.
* Number Keys
Keys are used for choosing a display or test by the
number for the test or display.
* READ/HOLD Key
Key is used to freeze any sensor display.
* MODE & ATM Key
Pressing MODE and ATM key at the same time will cause
DRB-II to reset to copyright screen.
ENTERING ON-BOARD DIAGNOSTICS (USING DRB-II)
* PLEASE READ THIS FIRST *
1) Before entering on-board diagnostics, refer to PRETEST
INSPECTION in this article. Turn ignition off. Locate self-diagnostic
connector. See SELF-DIAGNOSTIC TEST CONNECTOR LOCATION table in this
article. Using appropriate Mitsubishi cartridge and adapter, connect
DRB-II to diagnostic connector.
2) Ensure all accessories are off. Turn ignition on. All
character positions will illuminate and copyright information will
appear on screen for a few seconds.
3) If DRB-II screen displays an error message, refer to DRB-
II ERROR SCREENS in this article. The DRB-II will offer 4 menus:
VEHICLES TESTED, HOW TO USE, CONFIGURE and SELECT VEHICLE.
VEHICLES TESTED
Press "1" key or ENTER key when VEHICLES TESTED appears on
DRB-II. DRB-II shows models covered by cartridge. Screen will display
for 5 seconds and return to DRB-II menu. To return to DRB-II menu
sooner, press ATM key.
HOW TO USE
Press "2" key or press down arrow to display HOW TO USE
option and press ENTER. Press and hold F3 key. DRB-II displays
instructions for cartridge usage. To return to DRB-II menu, press ATM
key.
CONFIGURE