Mitsubishi Galant (2004+). Manual - part 1289

MULTIPORT FUEL INJECTION (MFI) DIAGNOSIS

TSB Revision

MULTIPORT FUEL INJECTION (MFI) <3.8L ENGINE>

13B-849

DTC P1603: Battery Backup Line Malfunction

.

TECHNICAL DESCRIPTION

• The PCM checks the open circuit of battery 

backup line.

NOTE: When the system detects an open circuit in 
the battery backup line, it makes 1 failure judgment 
of other diagnostic trouble codes (DTCs).

.

RED-WHITE

AK302869

RED-WHITE

WHITE

BATTERY

42

BATTERY
BACKUP

POWERTRAIN CONTROL
MODULE (PCM)

Battery Backup Circuit

B-20

9

20A

RELAY
BOX

22

21

23 24 25

26 27 28 29

30 31 32 33 34

35 36 37 38

39 40 41 42 43

AK303085

CONNECTOR: B-20

PCM

AB

AIR CLEANER

B-20

MULTIPORT FUEL INJECTION (MFI) DIAGNOSIS

TSB Revision

MULTIPORT FUEL INJECTION (MFI) <3.8L ENGINE>

13B-850

DESCRIPTIONS OF MONITOR METHODS
Battery backup line voltage is under specified value.

.

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)

• Not applicable

Sensor (The sensor below is determined to be 

normal)

• Not applicable

.

DTC SET CONDITIONS

Logic Flow Chart

.

Check Conditions

• Engine starting sequence was completed.

• Battery positive voltage is higher than 10 volts.

Judgement Criteria

• Battery backup line voltage has continued to be 6 

volts or lower for 2 seconds.

.

OBD-II DRIVE CYCLE PATTERN
None.

.

START

MONITORING
CONDITIONS

CIRCUIT VOLTAGE

MALFUNCTION

CONTINUOUS

FAILURE FOR 2secs

NO

YES

YES

NO

< 6V

END

GOOD

NO

Yes

AK302411

MULTIPORT FUEL INJECTION (MFI) DIAGNOSIS

TSB Revision

MULTIPORT FUEL INJECTION (MFI) <3.8L ENGINE>

13B-851

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

• Open or shorted battery backup line, harness 

damage or connector damage.

• PCM failed.

DIAGNOSIS

Required Special Tools:

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

• MB991824: V.C.I.

• MB991827: USB Cable

• MB991910: Main Harness A

• MB991923: Power Plant ECU Check Harness

STEP 1. Using scan tool MB991958, read the diagnostic 
trouble code (DTC).

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) Turn the ignition switch to the "ON" position.

(3) Erase the DTC.
(4) Start the engine and run it at idle.
(5) Read the DTC.
(6) Turn the ignition switch to the "LOCK" (OFF) position.
Q: Is DTC P1603 set?

YES : Go to Step 2.
NO :  The inspection is complete.

AC305412

AB

MB991910

DATA LINK

CONNECTOR

MB991824

MB991827

MULTIPORT FUEL INJECTION (MFI) DIAGNOSIS

TSB Revision

MULTIPORT FUEL INJECTION (MFI) <3.8L ENGINE>

13B-852

STEP 2. Measure the backup power supply voltage at PCM 
connector B-20 by using power plant ECU check harness 
special tool MB991923.

(1) Disconnect the all PCM connectors and connect power 

plant ECU check harness special tool MB991923 between 
the separated connectors.

AK303092

25

21

24 23 22

29 28 27 26

34 33 32 31 30

38 37 36 35

43 42 41 40 39

CONNECTOR: B-20

B-20

PCM

AB

HARNESS CONNECTOR: 
COMPONENT SIDE

AIR CLEANER

AK203002

25

21

24 23 22

29 28 27 26

34 33 32 31 30

38 37 36 35

43 42 41 40 39

AB

POWER PLANT ECU 
CHECK HARNESS CONNECTOR

MB991923

PCM