Mitsubishi Galant 9G. Manual - part 741

MULTIPORT FUEL INJECTION (MFI) DIAGNOSIS

TSB Revision

MULTIPORT FUEL INJECTION (MFI) <2.4L ENGINE>

13A-406

13A

DTC P0171: System too Lean (cylinder 1, 4)

CAUTION

If DTC P0171 has been set, TCL related DTC 
U1120 is also set. After P0171 has been diag-
nosed, don't forget to erase DTC U1120.

.

Fuel Trim Circuit

• Refer to DTC P0201 − Injector Circuit-cylinder 1 

P.13A-464

, DTC P0204 

− Injector Circuit-cylinder 

4 

P.13A-494

.

.

CIRCUIT OPERATION

• Refer to DTC P0201 − Injector Circuit-cylinder 1 

P.13A-464

, DTC P0204 

− Injector Circuit-cylinder 

4 

P.13A-494

.

.

TECHNICAL DESCRIPTION

• If a malfunction occurs in the fuel system, the fuel 

trim value becomes too large.

• The PCM checks whether the fuel trim value is 

within a specified range.

.

DESCRIPTIONS OF MONITOR METHODS

Cylinder 1, 4 air/fuel learning value (long time fuel 

trim) and air/fuel feedback integral value (short 
time fuel trim) are too lean.

.

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)

• Misfire 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

.

<<PREVIOUS

MULTIPORT FUEL INJECTION (MFI) DIAGNOSIS

TSB Revision

MULTIPORT FUEL INJECTION (MFI) <2.4L ENGINE>

13A-407

DTC SET CONDITIONS
Logic Flow Chart

.

Check Conditions

• Engine coolant temperature is lower than 100°C 

(212

°F) when the engine is started.

• Intake air temperature is lower than 60°C (140°F) 

when the engine is started.

• Under the closed loop air/fuel ratio control.

• Engine coolant temperature is higher than 76°C 

(169

°F).

• Mass airflow sensor output is 6 g/sec or more.

Judgment Criteria

• Long-term fuel trim has continued to be higher 

than +12.5 percent for 5 seconds.

or

• Short-term fuel trim has continued to be higher 

than +10.0 percent for 5 seconds. <Federal>

or

• Short-term fuel trim has continued to be higher 

than +7.0 percent for 5 seconds. <California>

K

LRN

: LONG-TERM TRIM

K

I

: SHORT-TERM TRIM

K0 : MAXIMUM LIMIT OF LONG-TERM TRIM
K1 : MAXIMUM LIMIT OF SHORT-TERM TRIM
K2 : MINIMUM LIMIT OF LONG-TERM TRIM
K3 : MINIMUM LIMIT OF SHORT-TERM TRIM

START

MONITORING

CONDITIONS

END

NO

NO

NO

NO

NO

NO

YES

YES

YES

YES

YES

YES

K

LRN

 > K0

MALFUNCTION

GOOD

K

LRN

 < K2

K

I

< K3

K

I

> K1

CONTINUOUS FAILURE

FOR 5secs

AK204050

MULTIPORT FUEL INJECTION (MFI) DIAGNOSIS

TSB Revision

MULTIPORT FUEL INJECTION (MFI) <2.4L ENGINE>

13A-408

Check Conditions

• Engine coolant temperature is lower than 100°C 

(212

°F) when the engine is started.

• Intake air temperature is lower than 60°C (140°F) 

when the engine is started.

• Under the closed loop air/fuel ratio control.

• Engine coolant temperature is higher than 76°C 

(169

°F).

• Mass airflow sensor output is 6 g/sec or less.

Judgment Criteria

• Long-term fuel trim has continued to be higher 

than +12.5 percent for 5 seconds.

or

• Short-term fuel trim has continued to be higher 

than +15.0 percent for 5 seconds.

Check Conditions

• Engine coolant temperature is higher than 100°C 

(212

°F) when the engine is started.

• Intake air temperature is higher than 60°C 

(140

°F) when the engine is started.

• Under the closed loop air/fuel ratio control.

• Engine coolant temperature is higher than 76°C 

(169

°F).

• Mass airflow sensor output is 6 g/sec or more.

Judgment Criteria

• Long-term fuel trim has continued to be higher 

than +12.5 percent or 5 seconds.

or

• Short-term fuel trim has continued to be higher 

than +20.0 percent for 5 seconds.

Check Conditions

• Engine coolant temperature is higher than 100°C 

(212

°F) when the engine is started.

• Intake air temperature is higher than 60°C 

(140

°F) when the engine is started.

• Under the closed loop air/fuel ratio control.

• Engine coolant temperature is higher than 76°C 

(169

°F).

• Mass airflow sensor output is 6 g/sec or less.

Judgment Criteria

• Long-term fuel trim has continued to be higher 

than +12.5 percent or 5 seconds.

or

• Short-term fuel trim has continued to be higher 

than +25.0 percent for 5 seconds.

Check Conditions

• Engine coolant temperature is higher than 76°C 

(169

°F).

• Under the closed loop air/fuel ratio control.

Judgment Criteria

• Long-term fuel trim has continued to be +12.5 

percent for 2 seconds.

or

• Short-term fuel trim has continued to be +25.0 

percent for 2 seconds.

.

OBD-II DRIVE CYCLE PATTERN

Refer to Diagnostic Function 

− OBD-II Drive Cycle − 

Procedure 2 

− Fuel Trim Monitor 

P.13A-6

.

.

TROUBLESHOOTING HINTS (The most likely 

causes for this code to be set are:)

• Mass airflow sensor failed.

• Injector (Number 1, 4) failed.

• Incorrect fuel pressure.

• Air drawn in from gaps in gasket, seals, etc.

• Engine coolant temperature sensor failed.

• Intake air temperature sensor failed.

• Barometric pressure sensor failed.

• Manifold absolute pressure sensor failed.

• Exhaust leak.

• Use of incorrect or contaminated fuel.

• Harness damage in cylinder 1, 4 injector circuit or 

connector damage.

• PCM failed.

MULTIPORT FUEL INJECTION (MFI) DIAGNOSIS

TSB Revision

MULTIPORT FUEL INJECTION (MFI) <2.4L ENGINE>

13A-409

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 15.
NO :  Go to Step 2.

STEP 2. Check for intake system vacuum leak.
Q: Are there any abnormalities?

YES : Repair it. Then go to Step 15.
NO :  Go to Step 3.

STEP 3. Using scan tool MB991958, check data list item 12: 
Mass Airflow Sensor.

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 

12, Mass Airflow Sensor.

(4) Warm up the engine to normal operating temperature: 80

°C 

to 95

°C (176°F to 203°F).

• When idling, between 2.0 and 6.0 g/sec.

• When 2,500 r/min, between 6.5 and 14.5 g/sec.

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

YES : Go to Step 4.
NO :  Refer to DTC P0101 

− Mass Airflow Circuit 

Range/Performance Problem 

P.13A-46

, DTC P0102 

− Mass Airflow Circuit Low Input 

P.13A-55

, DTC 

P0103 

− Mass Airflow Circuit High Input 

P.13A-65

.

AK303804AB

MB991910

DATA LINK
CONNECTOR

MB991824

MB991827