Mitsubishi Galant (2004+). Manual - part 1571

SRS AIR BAG DIAGNOSIS

TSB Revision

SUPPLEMENTAL RESTRAINT SYSTEM (SRS)

52B-177

DIAGNOSIS

Required Special Tools:

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

• MB991824: Vehicle Communication Interface (V.C.I.)

• MB991827: MUT-III USB Cable

• MB991910: MUT-III Main Harness A

• MB991910: MUT-III Main Harness A (Vehicles with CAN 

communication system)

STEP 1. Using scan tool MB991958, diagnose the CAN bus 
line.

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. Refer to "How to connect the 

scan tool 

P.52B-30

."

(2) Turn the ignition switch to the "ON" position.
(3) Diagnose the CAN bus line.
(4) Turn the ignition switch to the "LOCK" (OFF) position.
Q: Is the CAN bus line found to be normal?

YES : Go to Step 2.
NO :  Repair the CAN bus line (Refer to GROUP 54C, 

Diagnosis 

P.54C-14

).

AC305412

AB

MB991910

DATA LINK

CONNECTOR

MB991824

MB991827

SRS AIR BAG DIAGNOSIS

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SUPPLEMENTAL RESTRAINT SYSTEM (SRS)

52B-178

STEP 2. Recheck for diagnostic trouble code.

Check again if the DTC is set.
(1) Erase the DTC.
(2) Turn the ignition switch to the "ON" position.
(3) Check if the DTC is set.
(4) Turn the ignition switch to the "LOCK" (OFF) position.
Q: Is the DTC set?

YES : Go to Step 3.
NO :  There is an intermittent malfunction such as poor 

engaged connector(s) or open circuit (Refer to 
GROUP 00, How to Cope with Intermittent 
Malfunction 

P.00-6

).

STEP 3. Check the side impact sensor (LH) power supply 
circuit. Measure the voltage at the side impact sensor (LH) 
connector D-21.
(1) Disconnect the negative battery terminal.

(2) Disconnect side impact sensor (LH) connector D-21, and 

measure at the wiring harness side.

(3) Connect the negative battery terminal.
(4) Turn the ignition switch to the "ON" position.

CAUTION

Do not insert a test probe into the terminal from its front 
side directly, as the connector contact pressure may be 
weakened.
(5) Measure the voltage between the D-21 harness side 

connector terminal 2 and body ground.

Voltage should measure 9 volts or more.

Q: Is the measured voltage within the specified range?

YES : Replace the side impact sensor (LH) (Refer to 

P.52B-377

). Then go to Step 5.

NO :  Go to Step 4.

AC305412

AB

MB991910

DATA LINK

CONNECTOR

MB991824

MB991827

AC305250

CONNECTOR: D-21

AD

FRONT SEAT BELT

HARNESS SIDE
CONNECTOR
(REAR VIEW)

2

1

AC201627

1 2

D-21 HARNESS SIDE
CONNECTOR
(REAR VIEW)

AR

SRS AIR BAG DIAGNOSIS

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SUPPLEMENTAL RESTRAINT SYSTEM (SRS)

52B-179

STEP 4. Check the harness wires for open circuit or short 
circuit between SRS-ECU connector C-122 (terminal No.19 
and 20) and side impact sensor (LH) connector D-21 
(terminal No.1 and 2).

Q: Are the harness wires between SRS-ECU connector 

C-122 (terminal No.19 and 20) and side impact sensor 
(LH) connector D-21 (terminal No.1 and 2) in good 
condition?
YES : Erase the diagnostic trouble code memory, and check 

the diagnostic trouble code. If DTC B1437 sets, 
replace the SRS-ECU (Refer to 

P.52B-365

). Then go 

to Step 5.

NO :  Replace the harness wires between SRS-ECU 

connector C-122 and side impact sensor (LH) 
connector D-21. Then go to Step 5.

STEP 5. Recheck for diagnostic trouble code.

Check again if the DTC is set.
(1) Erase the DTC.
(2) Turn the ignition switch to the "ON" position.

(3) Check if the DTC is set.
(4) Turn the ignition switch to the "LOCK" (OFF) position.
Q: Is DTC B1437 set?

YES : Return to Step 1.
NO :  The procedure is complete.

AC305362

CONNECTOR: C-122

C-122 (Y)

AI

SRS-ECU

C-122 
Harness side
connector 
(rear view)

A

B

18

10

15

7

13

5

14

6

16

8

17

9

19

11

20

12

1 2

3 4

AC305250

CONNECTOR: D-21

AD

FRONT SEAT BELT

HARNESS SIDE
CONNECTOR
(REAR VIEW)

2

1

AC305412

AB

MB991910

DATA LINK

CONNECTOR

MB991824

MB991827

SRS AIR BAG DIAGNOSIS

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SUPPLEMENTAL RESTRAINT SYSTEM (SRS)

52B-180

DTC B1438: Side Impact Sensor (LH) (Squib) for Power Supply Circuit
DTC B1439: Side Impact Sensor (LH) (Squib) for Communication System

CAUTION

If DTC B1438 or B1439 is set in the SRS-ECU, 
always diagnose the CAN main bus line.

.

CIRCUIT OPERATION
The side impact sensor includes an analog G sensor 
and CPU, etc. The CPU monitors the analog G sen-
sor output signal. If the CPU judges that the 
side-airbags should be deployed, it sends a fire sig-
nal to the SRS-ECU to deploy the side-airbags. In 
addition, the CPU diagnoses the internal compo-
nents of the side impact sensor. If a malfunction 
occurs, it requests the SRS-ECU to set a diagnostic 
trouble code.

.

DTC SET CONDITIONS
These DTCs are set if communication between the 
side impact sensor (LH) and the SRS-ECU is not 
possible or faulty.

.

TROUBLESHOOTING HINTS

• Damaged wiring harnesses or connectors

• Malfunction of the side impact sensor (LH)

• Malfunction of the SRS-ECU

.

SIDE IMPACT 
SENSOR (LH)

INTERFACE 
CIRCUIT

SRS-ECU

Side Impact Sensor (LH) Circuit

AC305362

CONNECTOR: C-122

C-122 (Y)

AE

SRS-ECU

AC305250

CONNECTOR: D-21

AC

FRONT SEAT BELT