Mitsubishi Lancer Evolution IX. Manual - part 426

TROUBLESHOOTING

MULTIPORT FUEL INJECTION (MPI)

13A-179

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.

STEP 9. Check harness between B-101 (terminal 
No. 2) EGR control solenoid valve connector and 
C-121 (terminal No. 6) engine-ECU connector.

NOTE: Before checking harness, check intermediate 
connector B-14, and repair if necessary.

• Check output line for damage.

Q: Is the check result normal?

YES : 

Go to Step 10 .

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>

AK305024

1

2

AB

Connector : B-101

Harness side 
connector

B-101(BR)

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-180

STEP 10. Check harness between B-101 (terminal 
No. 1) EGR control solenoid valve connector and 
B-12X (terminal No. 4) engine control relay 
connector.

NOTE: Before checking harness, check intermediate 
connector B-14, and repair if necessary.

• Check power supply line for damage.

Q: Is the check result normal?

YES : 

Go to Step 11 .

NO : 

Repair the damaged harness wire.

STEP 11. M.U.T.-II /III actuator test

• Item No. 10: EGR control solenoid valve

OK: Operating sound can be heard and the 
valve vibrates.

Q: Is the check result normal?

YES : 

Intermittent malfunction (Refer to GROUP 

00 

− How to Use 

Troubleshooting/Inspection Service Points 

P.00-5

).

NO : 

Replace the engine-ECU.

Code No. P0421: Warm up Catalyst Malfunction

FUNCTION

• The signal from the oxygen sensor (rear) differs 

from the oxygen sensor (front). That is because 
the catalytic converter purifies exhaust gas. 
When the catalytic converter has deteriorated, 
the signal from the oxygen sensor (front) 
becomes similar to the oxygen sensor (rear).

• The engine-ECU compares the output of the front 

and rear oxygen sensor signals.

TROUBLE JUDGMENT

Check Conditions

• The engine speed is 3,000 r/min. or less.

• The accelerator pedal is fully depressed.

• Airflow sensor output is 8 gm/s or higher.

• 3 seconds or longer has elapsed after the 

above-mentioned conditions have been met.

• Engine running, intake air temperature is −10°C 

or higher.

• Under the closed-loop control.

• Vehicle speed is 1.5 km/h or more.

• The engine-ECU monitors for this condition for 7 

cycles of 10 seconds each during the drive cycle.

• Short-term fuel trim is higher than −25% or lower 

than +25%.

• Accumulated air flow sensor output is 2,931 g or 

higher.

Judgment Criterion

• The oxygen sensor (rear) signal frequency 

divided by oxygen sensor (front) signal frequency 
= 0.8 or more.

AK305024

1

2

AB

Connector : B-101

Harness side 
connector

B-101(BR)

AK305003

2

1

3

4

AB

Connector : B-12X

B-12X

Harness side 
connector

Relay box’s
triangle marks

TROUBLESHOOTING

MULTIPORT FUEL INJECTION (MPI)

13A-181

PROBABLE CAUSES

• Catalytic converter deteriorated

• Failed oxygen sensor (front)

• Failed oxygen sensor (rear)

• Failed engine-ECU

DIAGNOSIS PROCEDURE

STEP 1. Check for leakage of exhaust emission 
from exhaust manifold.

Q: Is the check result normal?

YES : 

Go to Step 2 .

NO : 

Repair.

STEP 2. M.U.T.-II/III data list

• Refer to Data List Reference Table 

P.13A-372

.

a. Item No. 11: Oxygen sensor (front)
b. Item No. 59: Oxygen sensor (rear)

Q: Is the check result normal?

YES : 

Go to Step 3 .

NO : 

Perform the diagnosis code classified check 
procedure for the sensor that has shown an 
abnormal data valve (Refer to Inspection 
Chart for Diagnosis Codes 

P.13A-17

).

STEP 3. M.U.T.-II/III data list

• Item No. 11: Oxygen sensor (front)

OK: 0 

− 0.4 and 0.6 − 1.0 volt should alternate 

15 times or more within 10 seconds (engine 
speed at 2,000 r/min.).

Q: Is the check result normal?

YES : 

Go to Step 4 .

NO : 

Replace the oxygen sensor (front).

STEP 4. Replace the oxygen sensor (rear).

• After replacing the oxygen sensor (rear), 

re-check the trouble symptoms.

Q: Is the check result normal?

YES : 

The check is end.

NO : 

Go to Step 5 .

STEP 5. Replace the catalytic converter.

• After replacing the catalytic converter, re-check 

the trouble symptoms.

Q: Is the check result normal?

YES : 

The check is end.

NO : 

Replace the engine-ECU.

TROUBLESHOOTING

MULTIPORT FUEL INJECTION (MPI)

13A-182

Code No. P0443: Purge Control Solenoid Valve System

OPERATION

• Power is supplied to the purge control solenoid 

valve (terminal No. 2) from the engine control 
relay (terminal No. 4).

• The engine-ECU (terminal No. 16) makes the 

power transistor in the unit be in "ON" position, 
and that makes currents go on the purge control 
solenoid valve (terminal No. 1).

1

2

3

4

2

1

AK501815

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

Engine control relay

B-12X

16

Engine-ECU

B-02

MU802779

Purge control solenoid valve

1

2

Purge control solenoid valve circuit

R-Y

Y-G

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

C-121

(MU803784)

AB

Battery

B-Y

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

B-Y

B-Y

NOTE

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

2

1

4

3

To engine-ECU