Mitsubishi Montero Sport (2004+). Manual - part 270

MULTIPORT FUEL INJECTION (MFI) DIAGNOSIS

TSB Revision

MULTIPORT FUEL INJECTION (MFI)

13A-493

STEP 9. Check connector C-89 at PCM for damage.
Q: Is the connector in good condition?

YES : Go to Step 10.
NO :  Repair or replace it. Refer to GROUP 00E, Harness 

Connector Inspection 

P.00E-2

. Then go to Step 12.

STEP 10. Check for harness damage between MFI relay 
connector C-59 (terminal No. 1) and EGR vacuum regulator 
solenoid valve connector A-11 (terminal No. 1).

NOTE: Check harness after checking intermediate connector 
C-14. If intermediate connector is damaged, repair or replace it. 
Refer to GROUP 00E, Harness Connector Inspection 

P.00E-2

. 

Then go to Step 12.
Q: Is the harness wire in good condition?

YES : Go to Step 11.
NO :  Repair it. Then go to Step 12.

AK103914

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-89

C-89(GR)

HARNESS CONNECTOR:
COMPONENT SIDE

AK200023

2 1

3

4

CONNECTOR: C-59

AB

C-59

HARNESS 
CONNECTOR:
COMPONENT 
SIDE

AK200025

AK200025

1

2

CONNECTOR: A-11

AB

A-11(BR)

HARNESS CONNECTOR:
COMPONENT SIDE

MULTIPORT FUEL INJECTION (MFI) DIAGNOSIS

TSB Revision

MULTIPORT FUEL INJECTION (MFI)

13A-494

STEP 11. Check for harness damage between EGR vacuum 
regulator solenoid valve connector A-11 (terminal No. 2) 
and PCM connector C-89 (terminal No. 6).
Q: Is the harness wire in good condition?

YES : Replace the PCM. Then go to Step 12.
NO :  Repair it. Then go to Step 12.

STEP 12. Test the OBD-II drive cycle.
(1) Carry out a test drive with the drive cycle pattern. Refer to 

Diagnostic Function 

− OBD-II Drive Cycle − Procedure 6 − 

Other Monitor 

P.13A-4

.

(2) Check the diagnostic trouble code (DTC). 
Q: Is DTC P0403 set?

YES : Repeat the troubleshooting.
NO :  The procedure is complete.

AK200025

AK200025

1

2

CONNECTOR: A-11

AB

A-11(BR)

HARNESS CONNECTOR:
COMPONENT SIDE

AK103914

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-89

C-89(GR)

HARNESS CONNECTOR:
COMPONENT SIDE

MULTIPORT FUEL INJECTION (MFI) DIAGNOSIS

TSB Revision

MULTIPORT FUEL INJECTION (MFI)

13A-495

DTC P0421: Warm Up Catalyst Efficiency Below Threshold (bank 1)

.

TECHNICAL DESCRIPTION

• The signal from the rear heated oxygen sensor 

differs from the front heated oxygen sensor. That 
is because the catalytic converter purifies 
exhaust gas. When the catalytic converter has 
deteriorated, the signal from the front heated oxy-
gen sensor becomes similar to the rear heated 
oxygen sensor.

• The PCM compares the output of the front and 

rear heated oxygen sensor signals.

.

DESCRIPTIONS OF MONITOR METHODS
Front and rear oxygen sensor rich/lean switching fre-

quencies are nearly equal.

.

MONITOR EXECUTION
Continuous

.

MONITOR EXECUTION CONDITIONS (Other 
monitor and Sensor)

Other Monitor (There is no temporary DTC stored 

in memory for the item monitored below)

• Heated oxygen sensor (front) monitor

• Heated oxygen sensor (rear) monitor

• Heated oxygen sensor heater (front) monitor

• Heated oxygen sensor heater (rear) monitor

• Misfire monitor

• Fuel system monitor

• Air/fuel ratio feedback monitor

Sensor (The sensor below is determined to be 

normal)

• Volume airflow sensor

• Engine coolant temperature sensor

• Intake air temperature sensor

• Barometric pressure sensor

• Throttle position sensor

.

DTC SET CONDITIONS

Logic Flow Chart

.

START

MONITORING

CONDITIONS

Rf > R0

MALFUNCTION

GOOD

END

NO

NO

YES

YES

CALCULATE AVERAGE FREQUENCY

RATIO (Rf = Fr/Ff) OF SPECIFIED TIMES

R0: AVERAGE THRESHOLD VALUE.
R1: REAL TIME THRESHOLD VALUE.

AK204058

MULTIPORT FUEL INJECTION (MFI) DIAGNOSIS

TSB Revision

MULTIPORT FUEL INJECTION (MFI)

13A-496

Check Conditions

• Engine speed is lower than 3,000 r/min.

• Volume airflow sensor output frequency is 

between 69 and 169 Hz.

• Intake air temperature is higher than −10°C 

(14

°F).

• Barometric pressure is higher than 76 kPa (22.4 

in.Hg).

• The throttle valve is open.

• Under the closed loop air / fuel ratio control.

• Vehicle speed is 1.5 km/h (0.93 mph) or more.

• The PCM monitors for this condition for 7 cycles 

of 12 seconds each during the drive cycle.

• Short-term fuel trim is higher than −30 percent 

and lower than +25 percent.

• The cumulative volume airflow sensor output fre-

quency is higher than 4,000 Hz.

Judgment Criteria

• The right bank heated oxygen sensor (rear) sig-

nal frequency divided by right bank heated oxy-
gen sensor (front) signal frequency = 0.75 or 
more.

.

OBD-II DRIVE CYCLE PATTERN
Refer to Diagnostic Function 

− OBD-II Drive Cycle − 

Procedure 3 

− Catalytic Converter Monitor 

P.13A-4

.

.

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

• Right bank side catalytic converter deteriorated.

• Right bank heated oxygen sensor failed.

• Exhaust leaks

• PCM failed.

DIAGNOSIS

Required Special Tools:

• MB991958: Scan Tool (MUT-III Sub Assembly)

• MB991824: V.C.I

• MB991827: USB Cable

• MB991911: Main Harness B

STEP 1. Check for exhaust leaks.
Q: Are there any abnormalities?

YES : Repair it. Then go to Step 7.
NO :  Go to Step 2.