Mitsubishi 380. Manual - part 483

MULTIPOINT FUEL INJECTION (MPI) DIAGNOSIS

MULTIPOINT FUEL INJECTION (MPI)

13A-24

DIAGNOSTIC TROUBLE CODE PROCEDURES

DTC P0031: Heated Oxygen Sensor Heater Circuit low (bank 1, sensor 1).

.

CIRCUIT OPERATION

• Power is supplied from the MPI relay (terminal 

No. 4) to the right bank heated oxygen sensor 
(front) heater.

• The ENGINE-ECU (terminal No. 47) controls 

continuity to the right bank heated oxygen sensor 
(front) heater by turning the power transistor in 
the ENGINE-ECU "ON" and "OFF".

.

TECHNICAL DESCRIPTION

• The ENGINE-ECU checks whether the heater 

current is within a specified range when the 
heater is energized.

• The ENGINE-ECU checks whether the heater 

current is within a specified range when the 
heater is not energized.

.

1

2

3

4

1

2

3

4

1

2

3

4

1

2

3

4

AK303014

CONNECTOR: B-17X

MFI RELAY

MFI RELAY

FRONT OF VEHICLE

B-17X

AB

16DB400A

COVER

ENGINE

CONTROL

UNIT

AIR

CLEANER

AK303047

B-09 (B)

CONNECTOR: B-09

THROTTLE BODY

RIGHT BANK

HEATED OXYGEN

SENSOR (FRONT)

AB

MULTIPOINT FUEL INJECTION (MPI) DIAGNOSIS

MULTIPOINT FUEL INJECTION (MPI)

13A-25

DTC SET CONDITIONS

Check Conditions

• Battery voltage is between 10.7 - 16.1 volts.

• Engine starting sequence is completed.

• Engine speed is above 20 r/min.

• Oxygen sensor heater is active.

Judgment Criteria

• The heater voltage is less than 2.4 V during the 

calibrated time interval.
or

• The heater voltage is not within 2.4 - 3.6 Volts 

during the calibrated time interval.

• MIL is activated after 2 Driving Cycles.

• No limp home mode.

.

EOBD DRIVE CYCLE PATTERN

Refer to Diagnostic Function 

− EOBD Drive Cycle − 

P.13A-11

.

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TROUBLESHOOTING HINTS (The most 
likely causes for this code to be set are: )

• Open or shorted right bank heated oxygen sen-

sor (front) heater circuit, harness damage, or 
connector damage.

• Open circuit in right bank heated oxygen sensor 

(front) heater.

• Refer to component locations GROUP-

70

• Refer to configuration diagrams GROUP-

80

• Refer to circuit diagrams GROUP-

90

DIAGNOSIS

Required Special Tools:

•  Diagnostic tool (MUT-III Sub Assembly)

• MB991824: V.C.I.

• MB991827: USB Cable

• MB991910: Main Harness A

• MB992044:  ENGINE-ECU Check Harness

STEP 1. Check harness connector B-09 at the right bank 
heated oxygen sensor (front) for damage.
Q: Is the harness connector in good condition?

YES : Go to Step 2.
NO :  Repair or replace it. Refer to GROUP 00E, Harness 

Connector Inspection 

P.00E-2

. Then go to Step 11.

1

2

3

4

AK303048

B-09 (B)

CONNECTOR: B-09

THROTTLE BODY

RIGHT BANK

HEATED OXYGEN

SENSOR (FRONT)

AB

HARNESS

CONNECTOR:

COMPONENT SIDE

MULTIPOINT FUEL INJECTION (MPI) DIAGNOSIS

MULTIPOINT FUEL INJECTION (MPI)

13A-26

STEP 2. Check the right bank heated oxygen sensor 
(front).
(1) Disconnect right bank heated oxygen sensor (front) 

connector B-09.

(2) Measure the resistance between heated oxygen sensor 

connector terminal No. 3 and terminal No. 4.

Standard value: 9.0 

− 11.0 ohms [at 20°C (68°F)]

Q: Is the measured resistance between 9.0 and 11.0 ohms 

[at 20

°C (68°F)]?

YES : Go to Step 3.
NO :  Replace the right bank heated oxygen sensor (front). 

Then go to Step 11.

1

2

3

4

AK303048

B-09 (B)

CONNECTOR: B-09

THROTTLE BODY

RIGHT BANK

HEATED OXYGEN

SENSOR (FRONT)

AB

HARNESS

CONNECTOR:

COMPONENT SIDE

MULTIPOINT FUEL INJECTION (MPI) DIAGNOSIS

MULTIPOINT FUEL INJECTION (MPI)

13A-27

STEP 3. Measure the power supply voltage at right bank 
heated oxygen sensor (front) harness side connector B-09.
(1) Disconnect the connector B-09 and measure at the harness 

side.

(2) Turn the ignition switch to the "ON" position.

(3) Measure the voltage between terminal No. 3 and ground.

• Voltage should be battery positive voltage.

(4) Turn the ignition switch to the "LOCK" (OFF) position.

Q: Is battery positive voltage (approximately 12 volts) 

present?
YES : Go to Step 5.
NO :  Go to Step 4.

1

2

3

4

AK303048

B-09 (B)

CONNECTOR: B-09

THROTTLE BODY

RIGHT BANK

HEATED OXYGEN

SENSOR (FRONT)

AB

HARNESS

CONNECTOR:

COMPONENT SIDE

03DB200A

B-09 HARNESS 

CONNECTOR: 

COMPONENT SIDE

1

2

3

4