Mitsubishi Galant 9G. Manual — part 789

MULTIPORT FUEL INJECTION (MFI) DIAGNOSIS

TSB Revision

MULTIPORT FUEL INJECTION (MFI) <2.4L ENGINE>

13A-598

13A

DTC P0421: Warm Up Catalyst Efficiency Below Threshold (cylinder 1, 4)

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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 heated oxygen sensor rich/lean

switching frequencies are nearly equal.

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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)

• Mass airflow sensor

• Engine coolant temperature sensor

• Intake air temperature sensor

• Barometric pressure sensor

• Throttle position sensor

• Accelerator pedal position sensor

.

DTC SET CONDITIONS
Logic Flow Chart

.

START

MONITORING

CONDITIONS

MALFUNCTION

GOOD

END

NO

NO

YES

YES

Rf > R0

CALCULATE AVERAGE FREQUENCY

RATIO (Rf = Fr/Ff) OF SPECIFIED TIMES

R0: AVERAGE THRESHOLD VALUE.

AK302038

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MULTIPORT FUEL INJECTION (MFI) DIAGNOSIS

TSB Revision

MULTIPORT FUEL INJECTION (MFI) <2.4L ENGINE>

13A-599

Check Conditions

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

• Accelerator pedal is open.

• Mass airflow is between 14 and 45 g/sec.

• More than 3 seconds have elapsed after the

above-mentioned three conditions have been
met.

• Intake air temperature is higher than −10°C

(14

°F).

• Barometric pressure is higher than 76 kPa (22.4

in.Hg).

• Under the closed loop air/fuel ratio control.

• Vehicle speed is 1.5 km/h (1.0 mph) or more.

• The PCM monitors for this condition for 5 cycles

of 10 seconds each during the drive cycle.

• Short-term fuel trim is higher than −25 percent

and lower than +25 percent.

• The cumulative mass airflow is higher than 1,638

g.

Judgment Criteria

• The frequency ratio of cylinder 1, 4 heated oxy-

gen sensor (rear) and cylinder 1, 4 heated oxy-
gen sensor (front) is more than 0.7. <Federal>

or

• The frequency ratio of cylinder 1, 4 heated oxy-

gen sensor (rear) and cylinder 1, 4 heated oxy-
gen sensor (front) is more than 0.6. <California>

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OBD-II DRIVE CYCLE PATTERN

Refer to Diagnostic Function

− OBD-II Drive Cycle −

Procedure 3

− Catalytic Converter Monitor

P.13A-6

.

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

• Cylinder 1, 4 side catalytic converter deteriorated.

• Cylinder 1, 4 heated oxygen sensor failed.

• Exhaust leak.

• PCM failed.

DIAGNOSIS

Required Special Tools:

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

• MB991824: V.C.I.

• MB991827: USB Cable

• MB991910: Main Harness A

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

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

MULTIPORT FUEL INJECTION (MFI) DIAGNOSIS

TSB Revision

MULTIPORT FUEL INJECTION (MFI) <2.4L ENGINE>

13A-600

STEP 2. Using scan tool MB991958, check data list item 69:
Cylinder 1, 4 Heated Oxygen Sensor (rear).

CAUTION

To prevent damage to scan tool MB991958, always turn the
ignition switch to the "LOCK" (OFF) position before con-
necting or disconnecting scan tool MB991958.
(1) Connect scan tool MB991958 to the data link connector.
(2) Start the engine and run at idle.
(3) Set scan tool MB991958 to the data reading mode for item

69, Cylinder 1, 4 Heated Oxygen Sensor (rear).

• Warming up the engine. When the engine is revved, the

output voltage should repeat 0 volt and 0.6 to 1.0 volt
alternately.

(4) Turn the ignition switch to the "LOCK" (OFF) position.
Q: Is the sensor operating properly?

YES : Go to Step 3.
NO : Refer to DTC P0136

− Cylinder 1, 4 Heated Oxygen

Sensor Circuit (Sensor 2)

P.13A-250

, DTC P0137

−

Cylinder 1, 4 Heated Oxygen Sensor Circuit Low
Voltage (Sensor 2)

P.13A-268

, DTC P0138

− Cylinder

1, 4 Heated Oxygen Sensor Circuit High Voltage
(Sensor 2)

P.13A-275

, DTC P0139

− Cylinder 1, 4

Heated Oxygen Sensor Circuit Slow Response
(Sensor 2)

P.13A-280

.

STEP 3. Using scan tool MB991958, check data list item 39:
Cylinder 1, 4 Heated Oxygen Sensor (front).
(1) Start the engine and run at idle.
(2) Set scan tool MB991958 to the data reading mode for item

39, Cylinder 1, 4 Heated Oxygen Sensor (front).

• Warming up the engine. When the engine is revved, the

output voltage should be 0.6 to 1.0 volt.

(3) Turn the ignition switch to the "LOCK" (OFF) position.
Q: Is the sensor operating properly?

YES : Go to Step 4.
NO : Refer to DTC P0130

− Cylinder 1, 4 Heated Oxygen

Sensor Circuit (Sensor 1)

P.13A-192

, DTC P0131

−

Cylinder 1, 4 Heated Oxygen Sensor Circuit Low
Voltage (Sensor 1)

P.13A-210

, DTC P0132

− Cylinder

1, 4 Heated Oxygen Sensor Circuit High Voltage
(Sensor 1)

P.13A-217

, DTC P0133

− Cylinder 1, 4

Heated Oxygen Sensor Circuit Slow Response
(Sensor 1)

P.13A-222

, DTC P0134

− Cylinder 1, 4

Heated Oxygen Sensor Circuit No Activity Detected
(Sensor 1)

P.13A-228

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AK303804AB

MB991910

DATA LINK
CONNECTOR

MB991824

MB991827

AK303804AB

MB991910

DATA LINK
CONNECTOR

MB991824

MB991827

MULTIPORT FUEL INJECTION (MFI) DIAGNOSIS

TSB Revision

MULTIPORT FUEL INJECTION (MFI) <2.4L ENGINE>

13A-601

STEP 4. Using scan tool MB991958, check data list item 39:
Cylinder 1, 4 Heated Oxygen Sensor (front).
(1) Start the engine and run at idle.
(2) Set scan tool MB991958 to the data reading mode for item

39, Cylinder 1, 4 Heated Oxygen Sensor (front).

(3) Keep the engine speed at 2,000 r/min.

• 0 − 0.4 and 0.6 − 1.0 volt should alternate 15 times or

more within 10 seconds.

(4) Turn the ignition switch to the "LOCK" (OFF) position.
Q: Is the sensor operating properly?

YES : Go to Step 5.
NO : Replace the cylinder 1, 4 heated oxygen sensor

(front). Then go to Step 7.

STEP 5. 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 3 −

Catalytic Converter Monitor

P.13A-6

.

(2) Read the diagnostic trouble code.
Q: Is DTC P0421 set?

YES : Replace the cylinder 1, 4 side catalytic converter.

Then go to Step 6.

NO : The inspection is complete.

STEP 6. 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 3 −

Catalytic Converter Monitor

P.13A-6

.

(2) Read the diagnostic trouble code.
Q: Is DTC P0421 set?

YES : Replace the PCM. Then go to Step 7.
NO : The inspection is complete.

AK303804AB

MB991910

DATA LINK
CONNECTOR

MB991824

MB991827