1998 MITSUBISHI MONTERO oxygen

Heated Oxygen Sensor (Front)
(Federal) Underside of vehicle, forward
of catalytic converter.
Heated Oxygen Sensor (Front)
(Left Bank) (Calif.) In left exhaust manifold.
Heated Oxygen Sensor (Front)
(Right Bank) (Calif.) In right exhaust manifold.
Heated Oxygen Sensor (Rear)
(Federal) Underside of vehicle, behind
catalytic converter.
Heated Oxygen Sensor (Rear) (Left Bank)
(Calif.) In left exhaust pipe, below
engine.
Heated Oxygen Sensor (Rear) (Right Bank)
(Calif.) In right exhaust pipe, below
engine.
Input Shaft Speed Sensor On side of transmission.
Intake Air Temperature Sensor Mounted on outside of
evaporator case.
Manifold Differential Pressure Sensor On top left rear of engine.
Output Shaft Speed Sensor On rear of transmission.

Fig. 14: Typical Pulsed Secondary Air Injection System
Courtesy of General Motors Corp.
OXYGEN SENSOR (O2)
The O2 sensor is mounted in the exhaust system where it
monitors oxygen content of exhaust gases. Some vehicles may use 2 O2
sensors. The O2 sensor produces a voltage signal which is proportional
to exhaust gas oxygen concentration (0-3%) compared to outside oxygen
(20-21%). This voltage signal is low (about .1 volt) when a lean
mixture is present and high (1.0 volt) when a rich mixture is present.\
As ECM compensates for a lean or rich condition, this voltage
signal constantly fluctuates between high and low, crossing a
reference voltage supplied by the ECM on the O2 signal line. This is
referred to as cross counts. A problem in the O2 sensor circuit should
set a related trouble code.
COMPUTERIZED ENGINE CONTROLS (CEC)
The CEC system monitors and controls a variety of
engine/vehicle functions. The CEC system is primarily an emission
control system designed to maintain a 14.7:1 air/fuel ratio under most
operating conditions. When the ideal air/fuel ratio is maintained, the
catalytic converter can control oxides of nitrogen (NOx), hydrocarbon
(HC) and carbon monoxide (CO) emissions.
The CEC system consists of the following sub-systems:
Electronic Control Module (ECM), input devices (sensors and switches)\
and output signals.

TROUBLE CODE DEFINITION
When DTC is obtained, refer to appropriate DTC test
procedure.
DIAGNOSTIC TROUBLE CODES (DTCS)
NOTE: DTCs can only be retrieved by using a scan tool. Listed DTCs
are retrieved using a generic scan tool. MUT II scan tool
can be used, but it may not read all DTCs. DTCS listed are
not used on all vehicles.
DTC P0100
Volume Airflow (VAF) circuit failure. Possible causes are:
connector or harness, or faulty VAF sensor.
DTC P0105
Barometric (BARO) pressure circuit failure. Possible causes
are: connector or harness, or faulty BARO pressure sensor.
DTC P0105
Manifold Absolute Pressure (MAP) circuit failure. Possible
causes are: connector or harness, or faulty MAP sensor.
DTC P0110
Intake Air Temperature (IAT) circuit failure. Possible causes\
are: connector or harness, or faulty VAF sensor.
DTC P0115
Engine Coolant Temperature (ECT) circuit failure. Possible
causes are: connector or harness, or faulty ECT sensor.
DTC P0120
Throttle Position (TP) circuit failure. Possible causes are:
connector or harness, or faulty TP sensor.
DTC P0125
Excessive time to enter closed loop fuel control. Possible
causes are: faulty front HO2S, HO2S connector or harness, or faulty
fuel injector.
DTC P0130
Front Heated Oxygen Sensor (HO2S) circuit failure. Possible
causes are: connector or harness, or faulty HO2S.
DTC P0135
Front Heated Oxygen Sensor (HO2S) heater circuit failure.
Possible causes are: connector or harness, or faulty HO2S.
DTC P0136
Rear Heated Oxygen Sensor (HO2S) circuit failure. Possible
causes are: connector or harness, or faulty HO2S.
DTC P0141
Rear Heated Oxygen Sensor (HO2S) heater circuit failure.
Possible causes are: connector or harness, or faulty HO2S.
DTC P0150
Heated Oxygen Sensor (HO2S) circuit failure (bank 2, sensor
1). Possible causes are: connector or harness, or HO2S.

DTC P0155
Heated Oxygen Sensor (HO2S) heater circuit failure (bank 2,
sensor 1). Possible causes are: connector or harness, or HO2S.
DTC P0156
Heated Oxygen Sensor (HO2S) circuit failure (bank 2, sensor
2). Possible causes are: connector or harness, or HO2S.
DTC P0161
Heated Oxygen Sensor (HO2S) heater circuit failure (bank 2,
sensor 2). Possible causes are: connector or harness, or HO2S.
DTC P0170
Fuel trim failure (bank 1). Possible causes are: intake air
leaks, cracked exhaust manifold, faulty VAF sensor frequency, HO2S,
injector, fuel pressure, ECT, IAT or BARO pressure sensor.
DTC P0173
Fuel trim failure (bank 2). Possible causes are: intake air
leaks, cracked exhaust manifold, faulty VAF sensor frequency, HO2S,
injector, fuel pressure, ECT, IAT or BARO pressure sensor.
DTC P0201
Cylinder No. 1 injector circuit failure. Possible causes are:
connector or harness, or faulty injector.
DTC P0202
Cylinder No. 2 injector circuit failure. Possible causes are:
connector or harness, or faulty injector.
DTC P0203
Cylinder No. 3 injector circuit failure. Possible causes are:
connector or harness, or faulty injector.
DTC P0204
Cylinder No. 4 injector circuit failure. Possible causes are:
connector or harness, or faulty injector.
DTC P0205
Cylinder No. 5 injector circuit failure. Possible causes are:
connector or harness, or faulty injector.
DTC P0206
Cylinder No. 6 injector circuit failure. Possible causes are:
connector or harness, or faulty injector.
DTC P0300
Random misfire detected. Possible causes are: connector or
harness, faulty ignition coil, ignition power transistor, spark plug,
ignition circuit, injector, HO2S, compression pressure, timing belt,
air intake system, fuel pressure, or CKP sensor.
DTC P0301
Cylinder No. 1 misfire detected. Possible causes are:
connector or harness, faulty ignition coil, ignition power transistor,
spark plug, ignition circuit, injector, HO2S, compression pressure,
timing belt, air intake system, fuel pressure, or CKP sensor.
DTC P0302
Cylinder No. 2 misfire detected. Possible causes are:
connector or harness, faulty ignition coil, ignition power transistor,
spark plug, ignition circuit, injector, HO2S, compression pressure,
timing belt, air intake system, fuel pressure, or CKP sensor.

test vehicle (if necessary) and attempt to duplicate conditions that
caused original complaint. Recheck for DTCs. If no DTCs are displayed,
go to INTERMITTENT DTCS .
DTC P0125: EXCESSIVE TIME TO ENTER CLOSED LOOP FUEL CONTROL
NOTE: For terminal identification, see TERMINAL IDENTIFICATION. For
circuit and wire color identification, see
L - WIRING DIAGRAMS article.
Specific self-diagnostic test not available from manufacturer
at time of publication. Check front heated oxygen sensor, fuel
injectors, and related connectors and harnesses. Also, see F - BASIC
TESTING article.
DTC P0130, P0135, P0150 & P0155: FRONT HEATED OXYGEN SENSOR
(HO2S) CIRCUIT FAILURE
NOTE: For terminal identification, see TERMINAL IDENTIFICATION. For
circuit and wire color identification, see
L - WIRING DIAGRAMS article.
1) If using scan tool, go to step 3). Disconnect front HO2S
connector. Install Test Harness (MB998464) between HO2S and HO2S
connector. Using DVOM, check resistance between specified HO2S
connector heater terminals. See
FRONT HO2S CONNECTOR TERMINAL IDENTIFICATION table. HO2S resistance
should be 11-18 ohms at 68
F (20C). If resistance is not as
specified, replace HO2S. If resistance is as specified, go to next
step.
2) Start and warm engine to operating temperature. Using
jumper wires, apply 12 volts and ground to specified HO2S connector
heater terminals. See FRONT HO2S CONNECTOR TERMINAL IDENTIFICATION
table. Using DVOM, check voltage between specified HO2S connector
output terminals, while repeatedly racing engine. If voltage is not .
6-1.0 volt, replace HO2S. If voltage is .6-1.0 volt, go to step 5).
FRONT HO2S CONNECTOR TERMINAL IDENTIFICATION TABLE









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Application (1) Heater Terminals No. Output Terminals No.
Montero & 3000GT ......... 1 & 3 ........................... 2 & 4
( 1) - First terminal listed is positive. Second terminal listed is
negative.









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3) Start and warm engine to operating temperature. Using scan
tool, read HO2S voltage. See HO2S ITEM LIST IDENTIFICATION table for
appropriate scan tool item number. While monitoring scan tool,
accelerate to 4000 RPM. Suddenly decelerate. Scan tool should read 0.2
volt or less. Suddenly accelerate. Scan tool should read 0.6-1.0 volt.
If voltage is not as specified, replace HO2S. If voltage is as
specified, go to next step.
HO2S ITEM LIST IDENTIFICATION TABLE









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Application Item No.
Montero - Federal
Front ......................................................... 11
Rear .......................................................... 59
Except Montero - Federal

Front
Left ........................................................ 39
Right ....................................................... 11
Rear
Left ........................................................ 69
Right ....................................................... 59









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4) While monitoring scan tool, accelerate to 2500 RPM and
decelerate to 700 RPM (idle). Scan tool should switch from 0.6-1.0
volt to 0.4 volt or less. If voltage is not as specified, replace
HO2S. If voltage is as specified, go to next step.
5) On 3000GT, go to next step. On Montero, disconnect HO2S
connector and MFI relay connector. Using DVOM, check for continuity
between HO2S connector terminal No. 1 and MFI relay connector terminal
No. 1. If continuity does not exist, repair wiring harness as
necessary. If continuity exists, go to step 7).
6) Disconnect HO2S connector. Turn ignition switch to ON
position. Using DVOM, check voltage between chassis ground and HO2S
connector terminal No. 1. If battery voltage does not exists, repair
wiring harness as necessary. If battery voltage exists, go to next
step.
7) Turn ignition switch to OFF position. With HO2S connector
disconnected, disconnect PCM connector. Using DVOM, check for open or
short circuit between specified HO2S connector terminal and PCM
connector terminal. See
FRONT HO2S-TO-PCM HARNESS TERMINAL IDENTIFICATION table. If open or
short circuit exists, repair wiring harness as necessary. If open or
short circuit does not exist, go to next step.
FRONT HO2S-TO-PCM HARNESS TERMINAL IDENTIFICATION TABLE









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Application HO2S Terminal No. PCM Terminal No.
Montero - Federal .......... 3 ....................... 3
4 ...................... 71
All Others .............. ( 1) 3 ...................... 3
( 2) 3 ...................... 4
( 1) 4 ..................... 71
( 2) 4 ..................... 72
( 1) - Left front HO2S.
( 2) - Right front HO2S.









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8) Using DVOM, check for continuity between chassis ground
and HO2S connector terminal No. 2. If continuity does not exist,
repair wiring harness as necessary. If continuity exists, go to next
step.
9) Condition required to set DTC is not present at this time.
Test is complete. Intermittent problem may exist. Road test vehicle
(if necessary) and attempt to duplicate conditions that caused
original complaint. Recheck for DTCs. If no DTCs are displayed, go to
INTERMITTENT DTCS .
DTC P0136, P0141, P0156 & P0161: REAR HEATED OXYGEN SENSOR
(HO2S) CIRCUIT FAILURE
NOTE: For terminal identification, see TERMINAL IDENTIFICATION. For
circuit and wire color identification, see
L - WIRING DIAGRAMS article.
1) If using scan tool, go to next step. Disconnect rear HO2S

original complaint. Recheck for DTCs. If no DTCs are displayed, go to
INTERMITTENT DTCS.
DTC P0170 & P0173: FUEL TRIM FAILURE
NOTE: For terminal identification, see TERMINAL IDENTIFICATION. For
circuit and wire color identification, see
L - WIRING DIAGRAMS article.
1) Specific self-diagnostic test not available from
manufacturer at time of publication. Check volume airflow sensor, fuel
injectors, engine coolant temperature sensor, intake air temperature
sensor, barometric or manifold absolute pressure sensor, heated oxygen
sensor. See appropriate DTC test. Check related connectors and
harnesses. See L - WIRING DIAGRAMS article.
2) Also check fuel pressure, check for intake air leaks, and
for cracked manifold. See F - BASIC TESTING article.
DTC P0201-P0206: FUEL INJECTOR CIRCUIT FAILURE
NOTE: For terminal identification, see TERMINAL IDENTIFICATION. For
circuit and wire color identification, see
L - WIRING DIAGRAMS article.
1) If using scan tool, go to step 3). Using a stethoscope or
long-bladed screwdriver, listen for clicking sound from each fuel
injector while engine is running or being cranked. If no sound is
heard from fuel injector(s), check fuel injector connections. Repair
connections as necessary. If connections are okay, go to next step.
2) Ensure engine coolant temperature is at 68
F (20C).
Disconnect fuel injector connector. Using DVOM, check resistance
between specified fuel injector terminals. See
FUEL INJECTOR TERMINAL IDENTIFICATION table. If resistance is not 2.0-
3.0 3000GT turbo or 13-16 ohms on all other models, replace fuel
injector(s). If resistance is as specified, go to step 6).
FUEL INJECTOR TERMINAL IDENTIFICATION TABLE









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Application Terminals No.
Montero ( 1) ........................................ 8 & 1
8 & 2
8 & 3
8 & 5
8 & 6
8 & 7
3000GT - Rear Bank ( 2)
Non-Turbo ........................................ 1 & 2
1 & 5
1 & 6
Turbo ............................................ 1 & 4
2 & 8
4 & 5
4 & 6
4 & 7
4 & 8
( 1) - Check resistance at intermediate fuel injector
connector (component side).
( 2) - Check resistance at rear fuel injector connector
(component side).









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L - WIRING DIAGRAMS article.
1) Specific self-diagnostic test is not available from
manufacturer at time of publication. Check ignition coil, power
transistor, spark plugs, fuel injectors, heated oxygen sensor,
crankshaft position sensor, and related connectors and harnesses.
2) Also check compression pressure, timing belt, fuel
pressure, and for intake air leaks. See F - BASIC TESTING article.
DTC P0325: KNOCK SENSOR (KS) NO. 1 CIRCUIT FAILURE
NOTE: This test applies to 3000GT equipped with DOHC engine only.
For terminal identification, see TERMINAL IDENTIFICATION. For
circuit and wire color identification, see
L - WIRING DIAGRAMS article.
1) Component or scan tool testing procedure not available
from manufacturer at time of publication. Turn ignition switch to OFF
position. Disconnect KS connector and PCM connector. Ground PCM
connector terminal No. 91. Go to next step.
2) Using DVOM, check for continuity between chassis ground
and KS connector terminal No. 1. If continuity does not exist, repair
wiring harness as necessary. If continuity exists, go to next step.
3) Remove jumper wire from PCM connector terminal No. 1.
Check for continuity between chassis ground and KS connector terminal
No. 2. If continuity does not exist, repair wiring harness as
necessary. If continuity exists, go to next step.
4) Test is complete. Intermittent problem may exist. Road
test vehicle (if necessary) and attempt to duplicate conditions that
caused original complaint. Recheck for DTCs. If no DTCs are displayed,
go to INTERMITTENT DTCS .
DTC P0335: CRANKSHAFT POSITION (CKP) SENSOR CIRCUIT FAILURE
NOTE: For terminal identification, see TERMINAL IDENTIFICATION. For
circuit and wire color identification, see
L - WIRING DIAGRAMS article.
NOTE: Procedures are provided by manufacturer for component
testing using an engine analyzer with oscilloscope
capability. Refer to manufacturer's operation manual for
instructions in use of oscilloscope.
1) If using scan tool, go to step 3). Disconnect CKP sensor
connector. Install Test Harness (MB991348) between CKP sensor and
connector. Using engine analyzer with oscilloscope capability, connect
special patterns probe to CKP sensor connector terminal No. 2. Go to
next step.
2) Start engine. Compare oscilloscope wave pattern with
known-good wave pattern. See Fig. 38. Verify wavelength (time)
decreases as engine RPM increases. If wave pattern fluctuates to left
or right, check for loose timing belt or an abnormality in sensor
pick-up disc. If a rectangular wave pattern is generated even when
engine is not started, substitute known-good CKP sensor. Repeat test.
If wave pattern is still abnormal, go to step 6).
Fig. 38: Identifying Known-Good CKP Sensor Wave Pattern
Courtesy of Mitsubishi Motor Sales of America