Mitsubishi Lancer Evolution IX. Manual - part 405

TROUBLESHOOTING

MULTIPORT FUEL INJECTION (MPI)

13A-95

Code No. P0141: Oxygen Sensor Heater (rear) System

OPERATION

• Power is supplied to the heater power terminal 

(terminal No. 3) of the oxygen sensor (rear) con-
nector from the engine control relay (terminal No. 
4).

• The heater (terminal No. 4) of the oxygen sensor 

(rear) connector is controlled by the power tran-
sistor in the engine-ECU (terminal No. 26).

1

2

3

4

AK501808

3 4

2

1

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

3132 33

34 35

1

10

B-12X

B-Y

B-Y

B-Y

R-Y

Oxygen sensor (rear)

3

2

4

1

To engine-ECU

Engine-ECU

26

L-Y

R-Y

Engine
control
relay

Oxygen sensor heater (rear) circuit

Battery

Wire colour code
B: Black  LG: Light green  G: Green  L: Blue  W: White  Y: Yellow  SB: Sky blue  BR: Brown  O: Orange  GR: Gray
R: Red  P: Pink  V: Violet  PU: Purple

AB

C-121

(MU803783)

6 <A-13> (*1) or
13 <C-31> (*2)

2

1

C-137

MU801446

NOTE

*1: L.H. drive vehicles
*2: R.H. drive vehicles

28

29

J/C (6)
C-105

4

3

To engine-ECU

TROUBLESHOOTING

MULTIPORT FUEL INJECTION (MPI)

13A-96

FUNCTION

• The power supply to the oxygen sensor heater 

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

• Heating the oxygen sensor heater (rear) 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 (rear) is ON.

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

• A/C relay: OFF

• Radiator fan: OFF

• The system voltage is 11 − 16 V.

Judgment Criterion

• The heater current of oxygen sensor (rear) heater 

0.2 A or less or 3.5 A or more for 4 seconds.

PROBABLE CAUSES

• Failed oxygen sensor heater (rear)

• Open/short circuit in oxygen sensor (rear) circuit 

or loose connector contact

• Failed engine-ECU

DIAGNOSIS PROCEDURE

STEP 1. Connector check: C-137 oxygen sensor 
(rear) connector

Q: Is the check result normal?

YES : 

Go to Step 2 .

NO : 

Repair or replace the connector.

STEP 2. Perform resistance measurement at 
C-137 oxygen sensor (rear) connector.

• Disconnect connector, and measure at sensor 

side.

• Resistance between terminal No. 3 and No. 4.

OK: 11 

− 18 Ω

Q: Is the check result normal?

YES : 

Go to Step 3 .

NO : 

Replace the oxygen (rear) sensor.

STEP 3. Perform voltage measurement at C-137 
oxygen sensor (rear) connector.

• Disconnect connector, and measure at harness 

side.

• Ignition switch: "ON"

• Voltage between terminal No. 3 and earth.

OK: System voltage

Q: Is the check result normal?

YES : 

Go to Step 5 .

NO : 

Go to Step 4 .

AK305013

2 1

3

4

AB

Oxygen sensor(rear)

Connector : C-137

Harness side 
connector

C-137

AK305013

2 1

3

4

AB

Oxygen sensor(rear)

Connector : C-137

Harness side 
connector

C-137

AK305013

2 1

3

4

AB

Oxygen sensor(rear)

Connector : C-137

Harness side 
connector

C-137

TROUBLESHOOTING

MULTIPORT FUEL INJECTION (MPI)

13A-97

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

Q: Is the check result normal?

YES : 

Check intermediate connector C-105, and 

repair if necessary. If intermediate 
connector are normal, check and repair 
harness between C-137 (terminal No. 3) 
oxygen sensor (rear) 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.

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

• Measure engine-ECU terminal voltage.

• Ignition switch: "ON"

• Voltage between terminal No. 26 and earth.

OK: System voltage

Q: Is the check result normal?

YES : 

Go to Step 8 .

NO : 

Go to Step 6 .

AK305003

2

1

3

4

AB

Connector : B-12X

B-12X

Harness side 
connector

Relay box’s
triangle marks

AK305013

2 1

3

4

AB

Oxygen sensor(rear)

Connector : C-137

Harness side 
connector

C-137

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-98

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.

STEP 7. Check harness between C-137 (terminal 
No. 4) oxygen sensor connector and C-121 
(terminal No. 26) 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.

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>

AK305013

2 1

3

4

AB

Oxygen sensor(rear)

Connector : C-137

Harness side 
connector

C-137

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>