Mitsubishi Galant 9G. Manual — part 1424

SRS AIR BAG DIAGNOSIS

TSB Revision

SUPPLEMENTAL RESTRAINT SYSTEM (SRS)

52B-106

CAUTION

If DTC B1413 <1st squib> or B1493 <2nd squib>
is set in the SRS-ECU, always diagnose the CAN
main bus line.

.

CIRCUIT OPERATION

• The SRS-ECU judges how severe a collision is

by detecting signals from the front impact sensors
and the front air bag analog G-sensor. If the
impact is over a predetermined level, the
SRS-ECU sends an ignition signal. At this time, if
the front air bag safing G-sensor is on, the SRS
air bag will inflate.

• The ignition signal is input to the air bag module

via the clock spring to inflate the air bag.

.

DTC SET CONDITIONS

This DTC is set if there is abnormal resistance
between the input terminals of the passenger's air
bag module (squib). However, if no DTC resets, the
SRS warning light will be switched off (DTC will be
retained).

.

TROUBLESHOOTING HINTS

• Damaged harness wires and connectors

• Short to the ground in the passenger's air bag

module (squib) harness

• Malfunction of the SRS-ECU

.

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 (Vehicles with CAN

Communication System)

• MB991865: Dummy resistor

• MB991866: Resister harness

AC305362

CONNECTOR: C-121

C-121 (Y)

AD

SRS-ECU

SRS AIR BAG DIAGNOSIS

TSB Revision

SUPPLEMENTAL RESTRAINT SYSTEM (SRS)

52B-107

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 ).

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 Use Troubleshooting/Inspection
Service Points

− How to Cope with Intermittent

Malfunctions ).

AC305412

AB

MB991910

DATA LINK

CONNECTOR

MB991824

MB991827

AC305412

AB

MB991910

DATA LINK

CONNECTOR

MB991824

MB991827

SRS AIR BAG DIAGNOSIS

TSB Revision

SUPPLEMENTAL RESTRAINT SYSTEM (SRS)

52B-108

STEP 3. Check the passenger's air bag module. (Using
scan tool MB991958, read the diagnostic trouble code.)
(1) Disconnect the negative battery terminal.
(2) Disconnect the passenger’s air bag module connector

C-110.

(3) Slide the outer housing of the clock spring side of

passenger’s air bag module connector C-110 in the arrow
direction shown, and disconnect the connector.

(4) Connect special tool MB991865 to special tool MB991866.

CAUTION

Do not insert a test probe into the terminal from its front
side directly, as the connector contact pressure may be
weakened.
(5) Insert special tool MB991866 into the harness side

connector C-110 (terminal No.1 and 2 <1st squib> or
terminal No.3 and 4 <2nd squib>) by backprobing.

(6) Connect the negative battery terminal.
(7) Erase the diagnostic trouble code memory, and check the

diagnostic trouble code.

Q: Is DTC B1413 <1st squib> B1493 <2nd squib> set?

YES : Go to Step 4.
NO : Replace the passenger's air bag module (Refer to

P.52B-368

). Then go to Step 6.

AC307137AC

C-110 (Y)

FRONT DECK
CROSSMEMBER

CONNECTOR: C-110

HARNESS SIDE
CONNECTOR
(REAR VIEW)

AC306561AD

OUTER HOUSING OF THE PASSENGER'S
AIR BAG MODULE CONNECTOR C-110

AC306760AB

MB991865 (DUMMY
RESISTOR: 3

Ω

)

MB991866
(RESISTOR HARNESS)

C-110 HARNESS
CONNECTOR

C-110
PASSENGER'S
AIR BAG MODULE
CONNECTOR

SRS AIR BAG DIAGNOSIS

TSB Revision

SUPPLEMENTAL RESTRAINT SYSTEM (SRS)

52B-109

STEP 4. Check the passenger's air bag module circuit.
Measure the resistance at the SRS-ECU connector C-121.
(1) Disconnect SRS-ECU connector C-121.

DANGER

To prevent the air bag from deploying unintentionally,
disconnect the passenger’s air bag module connec-
tor C-110 to short the squib circuit.

(2) Unclip passenger’s air bag module connector C-110.
(3) Disconnect the passenger's air bag module connector

C-110.

CAUTION

Do not insert a test probe into the terminal from its front
side directly, as the connector contact pressure may be
weakened.
(4) Check for continuity between C-121 harness side connector

terminals 27 and 28 <1st squib> or 30 and 31 <2nd squib>,
and body ground.
It should be open circuit.

Q: Does continuity exist?

YES : Go to Step 5.
NO : Erase the diagnostic trouble code memory, and check

the diagnostic trouble code. If DTC B1413 <1st
squib> B1493 <2nd squib> sets, replace the
SRS-ECU (Refer to

P.52B-365

). Then go to Step 6.

AC305362

CONNECTOR: C-121

C-121 (Y)

AH

SRS-ECU

C-121
HARNESS SIDE
CONNECTOR
(REAR VIEW)

42

31

38

27

21

41

28

39

22

30

25

47

36

33

44

34

45

37

48

26

29

23

40

32

43

35

46

24

B

A

AC307137AC

C-110 (Y)

FRONT DECK
CROSSMEMBER

CONNECTOR: C-110

HARNESS SIDE
CONNECTOR
(REAR VIEW)

AC301592

42

31

38

27

21

41

28

39

22

30

25

47

36

33

44

34

45

37

48

26

29

23

40

32

43

35

46

24

B

A

C-121 HARNESS SIDE
CONNECTOR (REAR VIEW)

<1ST SQUIB>

AC

AC308154

42

31

38

27

21

41

28

39

22

30

25

47

36

33

44

34

45

37

48

26

29

23

40

32

43

35

46

24

B

A

C-121 HARNESS SIDE
CONNECTOR (REAR VIEW)

<2ND SQUIB>

AB