1991 MITSUBISHI MONTERO ECU

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I - S YSTE M /C O M PO NEN T T E STS

1991 M it s u bis h i M onte ro
1991 ENGINE PERFORMANCE
System & Component Testing
Chrysler Motors: Ram-50
Mitsubishi: Montero, Pickup
INTRODUCTION
Before testing separate components or systems, perform
procedures in F - BASIC TESTING article in the ENGINE PERFORMANCE
Section. Since many computer controlled and monitored components set a
trouble code if they malfunction, also perform procedures in G - TESTS
W/CODES article in the ENGINE PERFORMANCE Section.
NOTE: Testing individual components does not isolate shorts or
opens. Perform all voltage tests with a Digital
Volt-Ohmmeter (DVOM) with a minimum 10-megohm input
impedance, unless stated otherwise in test procedure. Use
ohmmeter to isolate wiring harness shorts or opens.
COMPUTERIZED ENGINE CONTROLS
CONTROL UNIT
NOTE: To identify ECU power and ground circuits, see appropriate
L - WIRING DIAGRAMS article in the ENGINE PERFORMANCE
Section.
Ground Circuits
1) ECU is located near right kick panel. Turn ignition off.
Using an ohmmeter, check for continuity between ground and ECU
terminals No. 101 and 106. Resistance should be zero ohms. If
resistance is not zero ohms, repair open circuit between ECU connector
and ground.
2) Connect voltmeter negative lead to ground. Connect
positive lead to ECU ground terminals as in step 1). With vehicle
running, voltmeter should indicate less than one volt. If voltmeter
reading is greater than one volt, check for open, corrosion or loose
connection in ground circuit.
Power Circuits
ECU is located near right kick panel. Turn ignition on. Check
for battery voltage on ECU terminals No. 102 and 107. If battery
voltage is not present, check operation of MPI control relay. See
RELAYS under MOTORS, RELAYS & SOLENOIDS.
ENGINE SENSORS & SWITCHES
BAROMETRIC PRESSURE SENSOR
Sensor is a component part of airflow sensor assembly. See G
- TESTS W/CODES article in the ENGINE PERFORMANCE Section.
COOLANT TEMPERATURE SENSOR
1) Remove coolant temperature sensor located near thermostat
housing (2-wire connector). Place end of sensor in water with terminal\

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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

Figs. 1 and 2. After recording abnormal code(s), perform necessary
repair.
4) After repair, turn ignition off and disconnect negative
battery cable for 10 seconds to erase ECU memory. Reconnect power
supply and repeat self-diagnostics to confirm repair.
SELF-DIAGNOSTIC TEST CONNECTOR LOCATION TABLE









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Application Location
Colt, Colt 200, Colt Wagon & Summit
1.5L ................................ Next to fuse block
1.6L .................................. Right kick panel
Colt Wagon & Colt Vista
1.8L & 2.0L SOHC .................... Next to fuse block
Eclipse ............................... Next to fuse block
Galant ................................... Left kick panel
Mirage ................................... Left kick panel
Montero .......................... Inside top of glove box
Precis ................................... Left kick panel









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Fig. 1: Diagnostic Fault Chart (1 of 2)
Courtesy of Mitsubishi Motor Sales of America.

Press "3" key or press down arrow to display CONFIGURE option
and press ENTER. Configure allows user to customize DRB-II display.
For example, If metric system is more useful, select METRIC from the
menu. All selections in CONFIGURE option remain active until user
changes selection.
SELECT VEHICLE
1) This allows the user to enter information about vehicle
being tested. Usually, this option has more than one display screen.
Use ENTER key to enter vehicle information.
2) When all information about vehicle is entered, DRB-II will
display an information summary the technician has entered. DRB-II will
show an additional option marked CONFIRM. If information is correct,
press CONFIRM. DRB-II will display MAIN MENU.
MAIN MENU
The MAIN MENU represents all diagnostic functions available.
Functions are SYSTEM TESTS, READ FAULTS, STATE DISPLAYS, ACTUATOR
TESTS and ADJUSTMENTS. SYSTEM TESTS is NOT available.
READ FAULTS
This allows technician to read fault codes stored in ECU
memory.
STATE DISPLAYS
1) This allows technician to view conditions at signal level.
The 2 types of signals are analog and digital. Analog signals are
monitored at pins corresponding to vehicle harness splices (e.g. fuel
pump relay).
2) Digital signals correspond to data transmitted by the
system controllers. Both signals are displayed in common units (e.g.
temperature). Use up and down arrow keys on DRB-II to scroll through
displays available.
3) The following ENGINE state displays are available on DRB-
II:
* Module Information - This mode allows technician to read ECU
part number and application.
* Engine Sensors - This mode allows technician to look at
various engine sensors during engine operation.
* Inputs/Outputs - This mode allows technician to read input
and output states of various switches and sensors.
* Custom Display - This screen allows technician to set up
his/her own custom display. Two custom display screens can be
programmed into DRB-II.
* Minimum/Current/Maximum - The MIN/CURRENT/MAX display shows a
history of conditions for a specific sensor. When this option
is selected, maximum, current (static) and minimum values can\
be displayed for a specific sensor. To reset sensors to a
zero value, simply press ENTER key. This display may be used
to isolate intermittent faults. The MIN/CURRENT/MAX display
allows technician to observe operation of 6 different sensor
values. Information is displayed as a 3-digit number. The
first value displayed is the minimum reading, the second
number is the current reading and third valve is the maximum
reading. Typically sensors range between 2-252. Values less
than 2 or greater than 252 will usually indicate that a

sensor is shorted or disconnected. Watch minimum and maximum
values to help diagnose intermittent problems.
* Monitors - This screen shows technician sensors and system
controllers which affect fuel control, spark advance, RPM and
A/C relay. There are 4 different screens available. As an
example, screen No. 1 will show: airflow sensor, O2 sensor,
battery and fuel injector. All of these inputs affect fuel
control.
Actuator Tests
This mode allows technician to actuate injectors, fuel pump,
purge control, EGR solenoid, fuel pressure solenoid and wastegate.
Adjustments
This option provides a means for erasing fault code
information stored in ECU. Follow DRB-II instructions to accomplish
this task.
DRB-II ERROR SCREENS
ERROR SCREENS
SYSTEM FAULT ROM CHECK SUM XXXX Message
Cartridge or DRB-II failure.
SYSTEM FAULT KEYBOARD FAILURE Message
Restart DRB-II. Ensure DRB-II keys are not pressed during
power up. Another possibility is DRB-II failure.
SYSTEM FAULT ROM FAILURE XXXX
DRB-II failure.
SYSTEM FAULT EEPROM FAILURE
DRB-II failure.
SYSTEM FAILURE, COMMUNICATION FAILURE, REFER TO DIAGNOSTIC
PROCEDURES Message
Perform diagnostic connector test. See DRIVEABILITY TEST No.
8 (DR-8). Failure of Mitsubishi Motor Corporation (MMC) adapter is
another possibility.
SYSTEM FAILURE NO RESPONSE FROM ADAPTER or SYSTEM FAILURE
ADAPTER REQUIRED TO DIAGNOSE WITH THIS CARTRIDGE Message
Ensure you are using a correct Mitsubishi Motor Corporation
cartridge. Failure of MMC adapter is another possibility.
Fig. 3: 10-Way ECU Connector
Courtesy of Chrysler Motors.

Fig. 4: 18-Way ECU Connector
Courtesy of Chrysler Motors.
Fig. 5: 24-Way ECU Connector
Courtesy of Chrysler Motors.
Fig. 6: Self-Diagnostic Connector Terminal Identification
Courtesy of Mitsubishi Motor Sales of America.
FAULT CODES
FAULT CODES TABLE








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Fault Code System Fault Description
11 .................... Open or short in O2 sensor circuit
12 ............... Open or short in airflow sensor circuit
13 ...... Open or short in intake air temp. sensor circuit
14 .......................... Open or short in TPS circuit
15 (1) .... Open or short in motor position sensor circuit
21 ......... Open or short in coolant temp. sensor circuit
22 ........ No voltage change in crank angle sensor signal
23 ............... No voltage change in TDC sensor circuit
24 ( 2) .. No voltage change in vehicle speed sensor signal
25 ........... Open or short in barometric pressure sensor
31 ( 3) ........ Open or short in detonation sensor circuit
41 ..................... Open or short in injector circuit
42 .............. Open or short in fuel pump drive circuit
43 ( 4) ......... Open or short in EGR temp. sensor circuit

44 (5) ..... Open or short in either ignition coil circuit
( 1) - Except Montero & Sigma.
( 2) - Will not turn on CHECK ENGINE light.
( 3) - 2.0L turbo only.
( 4) - California only. Except Sigma.
( 5) - Chrysler Motors models only.









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CLEARING CODES
Using DRB-II, from main menu select ADJUSTMENTS. Enter ERASE
FAULTS. Follow DRB-II instructions to accomplish this task. If DRB-II
is not available, fault codes may be cleared by disconnecting negative
battery cable for at least 10 seconds, allowing ECU to clear fault
codes.
TEST CHARTS
* PLEASE READ THIS FIRST *
NOTE: The following charts are supplied for Chrysler Motors
vehicles.
NS-1: TESTING IGNITION CIRCUIT - 1.5L
Fig. 7: Circuit Diagram NS-1 (1.5L) (1 of 2)
Fig. 8: Circuit Diagram NS-1 (1.5L) (2 of 2)