Mitsubishi 380. Manual - part 628

MULTIPORT FUEL INJECTION (MPI) DIAGNOSIS

MULTIPORT FUEL INJECTION (MPI) <3.8L ENGINE>

13A-604

INSPECTION PROCEDURE 24: Power supply system and ignition switch - IG system.   

.

CIRCUIT OPERATION

• Battery positive voltage is applied to the MPI 

relay (terminals No. 1, No. 2).

• When the ignition switch is turned to the "ON" 

position, the battery positive voltage is applied to 
the ECU (terminal No. 43). When the battery pos-
itive voltage is applied, the ECU turns the power 
transistor in the ECU "ON" and grounds the MPI 
relay coil. With this, the MPI relay turns "ON" and 
the battery positive voltage is supplied to the 
ECU (terminals No. 51, No. 64) from the MPI 
relay (terminal No. 4).

• A battery positive voltage is constantly supplied 

to the ECU (terminal No. 42) as the backup 
power.

• The ECU (terminals No. 25, No. 29) is grounded 

to the vehicle body.

.

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

• Malfunction of the ignition switch.

• Malfunction of the MPI relay.

• Improper connector contact, open circuit or 

short-circuit harness wire.

• Disconnected ECU ground wire.

• Malfunction of the ECU.

• Refer to component locations GROUP-

70

• Refer to configuration diagrams GROUP-

80

• Refer to circuit diagrams GROUP-

90

DIAGNOSIS

STEP 1. Check harness connector B-17X at MPI relay for 
damage.
Q: Is the connector in good condition?

YES : Go to Step 2.
NO :  Repair or replace it. Refer to GROUP 00E, Harness 

Connector Inspection 

P.00E-2

. Then confirm that the 

malfunction symptom is eliminated.

1

2

3

4

AK303017

CONNECTOR: B-17X

FRONT OF VEHICLE

B-17X

AB

HARNESS

CONNECTOR:

COMPONENT SIDE

RELAY BOX

MULTIPORT FUEL INJECTION (MPI) DIAGNOSIS

MULTIPORT FUEL INJECTION (MPI) <3.8L ENGINE>

13A-605

STEP 2. Check the MPI relay.

CAUTION

Because it is not possible to distinguish the top and the 
bottom of the MPI relay, inspect it with the triangle mark 
printed on the relay facing upward.
(1) Remove the MPI relay.

(2) Check for continuity between the MPI relay terminals No. 2 

and No. 3.

• There should be continuity. (approximately 70 ohms)

(3) Use jumper wires to connect MPI relay terminal No. 2 to the 

positive battery terminal and terminal No. 3 to the negative 
battery terminal.

(4) Check for continuity between the MPI relay terminals No. 1 

and No. 4 while connecting and disconnecting the jumper 
wire at the negative battery terminal.

• Should be less than 2 ohms. (Negative battery terminal 

connected)

• Should be open loop. (Negative battery terminal discon-

nected)

(5)  Install the MPI relay.

Q: Is the measured resistance within the specified range?

YES : Go to Step 3.
NO :  Replace the MPI relay. Then confirm that the 

malfunction symptom is eliminated.

1

2

3

4

AK303017

CONNECTOR: B-17X

FRONT OF VEHICLE

B-17X

AB

HARNESS

CONNECTOR:

COMPONENT SIDE

RELAY BOX

AK204164

1 2

3 4

MFI RERAY 

SIDE 

CONNECTOR

AB

1 2

3 4

AK203257

MFI RELAY SIDE

CONNECTOR

AB

MULTIPORT FUEL INJECTION (MPI) DIAGNOSIS

MULTIPORT FUEL INJECTION (MPI) <3.8L ENGINE>

13A-606

STEP 3. Measure the power supply voltage at MPI relay 
harness side connector B-17X.

CAUTION

Because it is difficult to distinguish the top and bottom of 
the MPI relay connector at the wiring harness, inspect it by 
using triangle mark on the junction block as reference.
(1) Disconnect the connector B-17X and measure at the 

harness side.

(2) Measure the voltage between terminals No. 1, No. 2 and 

ground.

• Voltage should be battery positive voltage.

Q: Is battery positive voltage (approximately 12 volts) 

present?
YES : Go to Step 4.
NO :  Check harness connector A-13 at intermediate 

connector for damage, and repair or replace as 
required. Refer to, GROUP 00E, Harness Connector 
Inspection 

P.00E-2

. If intermediate connector is in 

good condition, repair harness wire between relay 
box (9) and MPI relay connector B-17X (terminals No. 
1, No. 2) because of open circuit. Then confirm that 
the malfunction symptom is eliminated.

1

2

3

4

AK303017

CONNECTOR: B-17X

FRONT OF VEHICLE

B-17X

AB

HARNESS

CONNECTOR:

COMPONENT SIDE

RELAY BOX

2 1

3

4

AK303247

B-17X HARNESS 

CONNECTOR: 

COMPONENT SIDE

AB

MULTIPORT FUEL INJECTION (MPI) DIAGNOSIS

MULTIPORT FUEL INJECTION (MPI) <3.8L ENGINE>

13A-607

STEP 4. Check harness connector B-20 and B-21 at ECU 
for damage.
Q: Is the harness connector in good condition?

YES : Go to Step 5.
NO :  Repair or replace it. Refer to GROUP 00E, Harness 

Connector Inspection 

P.00E-2

. Then confirm that the 

malfunction symptom is eliminated.

16DB400A

COVER

ENGINE

CONTROL

UNIT

AIR

CLEANER