Mitsubishi Lancer Evolution IX. Manual - part 402

TROUBLESHOOTING

MULTIPORT FUEL INJECTION (MPI)

13A-83

FUNCTION

• The power supply to the oxygen sensor heater 

(front) is controlled by the ON/OFF control of the 
power transistor in the engine-ECU.

• Heating the oxygen sensor heater (front) enables 

the oxygen sensor to provide good response 
even when the exhaust emission temperature is 
low.

TROUBLE JUDGMENT

Check Conditions

• The engine coolant temperature is 20°C or 

higher.

• The oxygen sensor heater: (front) is ON.

• The engine speed of 50 r/min. or more.

• A/C relay: OFF

• Radiator fan: OFF

• The system voltage is 11 − 16 V.

Judging Criterion

• The heater current of oxygen sensor heater 

(front) 0.2 A or less or 3.5 A or more for 4 sec-
onds.

PROBABLE CAUSES

• Failed oxygen sensor heater (front)

• Open/short circuit in oxygen sensor heater (front) 

circuit or loose connector contact

• Failed engine-ECU

DIAGNOSIS PROCEDURE

STEP 1. Connector check: B-113 oxygen sensor 
(front) connector

Q: Is the check result normal?

YES : 

Go to Step 2 .

NO : 

Repair or replace the connector.

STEP 2. Perform resistance measurement at 
B-113 oxygen sensor (front) connector.

• Disconnect connector, and measure at sensor 

side.

• Resistance between terminal No. 1 and No. 3.

OK: 4.5 

− 8.0 Ω

Q: Is the check result normal?

YES : 

Go to Step 3 .

NO : 

Replace the oxygen sensor (front).

AK305011

1

2

3

4

AB

Connector : B-113

Harness side 
connector

B-113(B)

Oxygen sensor(front)

AK305011

1

2

3

4

AB

Connector : B-113

Harness side 
connector

B-113(B)

Oxygen sensor(front)

TROUBLESHOOTING

MULTIPORT FUEL INJECTION (MPI)

13A-84

STEP 3. Perform voltage measurement at B-113 
oxygen sensor (front) connector.

• Disconnect connector, and measure at harness 

side.

• Ignition switch: "ON"

• Voltage between terminal No. 1 and earth.

OK: System voltage

Q: Is the check result normal?

YES : 

Go to Step 5 .

NO : 

Go to Step 4 .

STEP 4. Connector check: B-12X engine control 
relay connector

Q: Is the check result normal?

YES : 

Check and repair harness between B-113 

(terminal No. 1) oxygen sensor (front) 
connector and B-12X (terminal No. 4) 
engine control relay connector.

• Check power supply line for 

open/short circuit.

NO : 

Repair or replace the connector.

AK305011

1

2

3

4

AB

Connector : B-113

Harness side 
connector

B-113(B)

Oxygen sensor(front)

AK305003

2

1

3

4

AB

Connector : B-12X

B-12X

Harness side 
connector

Relay box’s
triangle marks

AK305011

1

2

3

4

AB

Connector : B-113

Harness side 
connector

B-113(B)

Oxygen sensor(front)

TROUBLESHOOTING

MULTIPORT FUEL INJECTION (MPI)

13A-85

STEP 5. Perform voltage measurement at C-121 
engine-ECU connector.

• Measure engine-ECU terminal voltage.

• Ignition switch: "ON"

• Voltage between terminal No. 3 and earth.

OK: System voltage

Q: Is the check result normal?

YES : 

Go to Step 8 .

NO : 

Go to Step 6 .

STEP 6. Connector check: C-121 engine-ECU 
connector

Q: Is the check result normal?

YES : 

Go to Step 7 .

NO : 

Repair or replace the connector.

AK501995

2

3

4

5

6

7

8

9

11

12

13

14

15

16

17

18

19

20

30

21

22

23

24

25

26

27

28

29

31

32

33

34

35

1

10

AB

Connector: C-121

C-121 (GR)

C-121 (GR)

Harness side connector

<L. H. drive vehicles>

<R. H. drive vehicles>

AK501995

2

3

4

5

6

7

8

9

11

12

13

14

15

16

17

18

19

20

30

21

22

23

24

25

26

27

28

29

31

32

33

34

35

1

10

AB

Connector: C-121

C-121 (GR)

C-121 (GR)

Harness side connector

<L. H. drive vehicles>

<R. H. drive vehicles>

TROUBLESHOOTING

MULTIPORT FUEL INJECTION (MPI)

13A-86

STEP 7. Check harness between B-113 (terminal 
No. 3) oxygen sensor connector and C-121 
(terminal No. 3) engine-ECU connector.

• Check earthing line for open/short circuit.

Q: Is the check result normal?

YES : 

Replace the engine-ECU.

NO : 

Repair the damaged harness wire.

STEP 8. Connector check: C-121 engine-ECU 
connector

Q: Is the check result normal?

YES : 

Go to Step 9 .

NO : 

Repair or replace the connector.

AK305011

1

2

3

4

AB

Connector : B-113

Harness side 
connector

B-113(B)

Oxygen sensor(front)

AK501995

2

3

4

5

6

7

8

9

11

12

13

14

15

16

17

18

19

20

30

21

22

23

24

25

26

27

28

29

31

32

33

34

35

1

10

AB

Connector: C-121

C-121 (GR)

C-121 (GR)

Harness side connector

<L. H. drive vehicles>

<R. H. drive vehicles>

AK501995

2

3

4

5

6

7

8

9

11

12

13

14

15

16

17

18

19

20

30

21

22

23

24

25

26

27

28

29

31

32

33

34

35

1

10

AB

Connector: C-121

C-121 (GR)

C-121 (GR)

Harness side connector

<L. H. drive vehicles>

<R. H. drive vehicles>