Mitsubishi 380. Manual — part 787

SRS AIR BAG DIAGNOSIS

SUPPLEMENTAL RESTRAINT SYSTEM (SRS)

52B-72

DTC B1412: Passenger’s (Front) Air Bag Module (1st Squib) System Fault for Power Supply Circuit
(Short-Circuited to Power Supply)

CAUTION

If DTC B1412 is set in the SRS-ECU, always diag-
nose 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 power supply in the passenger's air

bag module (squib) harness

• Malfunction of the SRS-ECU

• Refer to circuit diagrams GROUP-

90

• Refer to configuration diagrams GROUP-

80

.

DIAGNOSIS

Required Special Tools:

• MB991958: diagnostic 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: Resistor harness

52DB017A

C-110 (Y)

FRONT DECK
CROSSMEMBER

CONNECTOR: C-110

24DB062A

CONNECTOR: C-121

C-121 (Y)

SRS-ECU

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

INSTRUMENT

HARNESS

CONNECTOR

(REAR VIEW)

SRS AIR BAG DIAGNOSIS

SUPPLEMENTAL RESTRAINT SYSTEM (SRS)

52B-73

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

CAUTION

To prevent damage to diagnostic tool MB991958, always
turn the ignition switch to the "LOCK" (OFF) position
before connecting or disconnecting diagnostic tool
MB991958.
(1) Connect diagnostic tool MB991958. Refer to "How to

connect the diagnostic tool

P.52B-19

."

(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 ).

00DB076A

MB991910

DATA LINK

CONNECTOR

MB991824

MB991827

00DB076A

MB991910

DATA LINK

CONNECTOR

MB991824

MB991827

SRS AIR BAG DIAGNOSIS

SUPPLEMENTAL RESTRAINT SYSTEM (SRS)

52B-74

STEP 3. Check the passenger's air bag module. (Using
diagnostic 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) by testprobe.

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

diagnostic trouble code.

Q: Is DTC B1412 set?

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

P.52B-237

). Then go to Step 6.

52DB018A

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

SUPPLEMENTAL RESTRAINT SYSTEM (SRS)

52B-75

STEP 4. Check the passenger’s air bag module circuit.
Measure the voltage 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) 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) 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 C-121 harness side

connector terminals 37 and 36 and body ground.
Voltage should measure 0 volt.

Q: Is the measured voltage within the specified range?

YES : Erase the diagnostic trouble code memory, and check

the diagnostic trouble code. If DTC B1412 sets,
replace the SRS-ECU (Refer to

P.52B-234

). Then go

to Step 6.

NO : Go to Step 5.

24DB062A

CONNECTOR: C-121

C-121 (Y)

SRS-ECU

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

INSTRUMENT

HARNESS

CONNECTOR

(REAR VIEW)

52DB018A

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