Mitsubishi Galant (2004+). Manual - part 1250

MULTIPORT FUEL INJECTION (MFI) DIAGNOSIS

TSB Revision

MULTIPORT FUEL INJECTION (MFI) <3.8L ENGINE>

13B-693

NOTE: If the number of sudden pressure fluctua-
tions does not reach twenty during any one 
period of engine idling, or if the ignition switch is 
turned OFF, the counter will reset to zero.
NOTE: The conditions for deviating from idling 
operation are as follows:

.

•

Engine speed is greater than 2,500 r/min.

•

Vehicle speed is 15 km/h (9.3 mph) or 
greater.

•

Volumetric efficiency is 55 percent or greater.

.

OBD-ll DRIVE CYCLE PATTERN
Refer to Diagnostic Function 

− OBD-ll Drive Cycle − 

Procedure 1 

− Evaporative Emission System Leak 

Monitor 

P.13B-5

.

.

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

• Malfunction of the fuel tank differential pressure 

sensor.

• A damaged harness in the fuel tank differential 

pressure sensor circuit.

• Malfunction of the PCM.

.

OVERVIEW OF TROUBLESHOOTING

•  DTC P0451 can be set by a faulty fuel tank differ-

ential pressure sensor or related circuit, or PCM 
failure.

• To check for system blockage, do a performance 

test which uses a mechanical vacuum gauge and 
scan tool MB991958 set on the fuel tank differen-
tial pressure sensor (TANK PRS SNSR 73). The 
mechanical gauge reading is used to verify scan 
tool MB991958 reading. A comparison of the 
mechanical gauge with the reading on scan tool 
MB991958 will locate a problem in the system.

MULTIPORT FUEL INJECTION (MFI) DIAGNOSIS

TSB Revision

MULTIPORT FUEL INJECTION (MFI) <3.8L ENGINE>

13B-694

DIAGNOSIS

Required Special Tools:

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

• MB991824: V.C.I.

• MB991827: MUT-III USB Cable

• MB991910: MUT-III Main Harness A

• MB991658: Test Harness Set

• MB991923: Power Plant ECU Check Harness

STEP 1. Using scan tool MB991958, check data list item 73: 
Fuel Tank Differential Pressure 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) Disconnect hose H from the evaporative emission canister, 

and plug the hose.

(3) Turn the ignition switch to the "ON" position.
(4) Remove the fuel cap.
(5) Set scan tool MB991958 to the data reading mode.

• Item 73, Fuel Tank Differential Pressure Sensor.

• The fuel tank pressure reading on the scan tool 

should be 

−1.5 to 1.5 kPa (−0.443 to 0.443 inHg).

AC305412

AB

MB991910

DATA LINK

CONNECTOR

MB991824

MB991827

AC306778

AC

HOSE H

PLUG

MULTIPORT FUEL INJECTION (MFI) DIAGNOSIS

TSB Revision

MULTIPORT FUEL INJECTION (MFI) <3.8L ENGINE>

13B-695

(6) Connect the evaporative emission system pressure pump 

(Miller number 6872A) to the fuel tank filler tube by using 

fuel tank adapter (MLR-8382) and pressurize the fuel tank.

• The fuel tank pressure reading should increase.

(7) Turn the ignition switch to the "LOCK" (OFF) position. Then 

disconnect scan tool MB991958.

(8) Remove  the evaporative emission system pressure pump 

(Miller number 6872A) and the fuel tank adapter 
(MLR-8382), and reinstall the fuel cap.

(9) Connect hose H to the evaporative emission canister.
Q: Is the fuel tank pressure between 

−1.5 and 1.5 kPa 

(

−0.443 and 0.443 inHg)?

YES : It can be assumed that this malfunction is intermittent 

(Refer to GROUP 00, How to Use 
Troubleshooting/Inspection Service Points 

− How to 

Cope with Intermittent Malfunctions 

P.00-6

). Go to 

Step 17.

NO :  Go to Step 2.

AC306661

MULTIPORT FUEL INJECTION (MFI) DIAGNOSIS

TSB Revision

MULTIPORT FUEL INJECTION (MFI) <3.8L ENGINE>

13B-696

STEP 2. Measure the sensor output voltage at PCM 
connector B-20 by using check harness special tool 
MB991923. 

(1) Disconnect all the connectors from the PCM.

(2) Connect special tool MB991923 (check harness) between 

the PCM and the body-side harness connector.

(3) Turn the ignition switch to the "ON" position.
(4) Remove the fuel cap.

AC306248

B-20 HARNESS

CONNECTOR:

COMPONENT SIDE

AB

B-20

CONNECTOR: B-20

PCM

AIR
CLEANER

AC209793AJ

SPECIAL TOOL 23-PIN CONNECTOR
WITHOUT RED TAPE
(PCM CONNECTOR B-20)

B-20

PCM

MB991923

BODY SIDE
HARNESS