Mitsubishi 380. Manual - part 777

SRS AIR BAG DIAGNOSIS

SUPPLEMENTAL RESTRAINT SYSTEM (SRS)

52B-32

DTC B1401: Driver's Air Bag Module (1st Squib) System Fault 2 (Open in the Squib Circuit)

CAUTION

If DTC B1401  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 driver's side air 
bag module (squib). The most likely causes for 
this code to be set are the followings: 

• Open circuit in the driver's air bag module 

(squib) or harness

• Open circuit in the clock spring

• Malfunction of connector contact

However, if no DTC reset, the SRS warning light will 
be switched off (DTC will be retained). 

.

TROUBLESHOOTING HINTS

• Refer to circuit diagrams GROUP-

90

• Refer to configuration diagrams GROUP-

80

• Open circuit in the clock spring

• Open circuit due to improper neutral position of 

the clock spring

• Open circuit in the driver's air bag module (squib) 

circuit

• Disengaged driver's air bag module (squib) con-

nector

• Improper connector contact

• Malfunction of the SRS-ECU

.

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

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)

52DB006A

C-307 (Y)

CONNECTORS: C-305, C-307

CLOCK

SPRING

C-305 (Y)

SRS AIR BAG DIAGNOSIS

SUPPLEMENTAL RESTRAINT SYSTEM (SRS)

52B-33

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-34

STEP 3. Check the driver's air bag module. (Using 
diagnostic tool MB991958, read the diagnostic trouble 
code.)
(1) Disconnect the negative battery terminal.
(2) Slide the outer housing of the driver’ s air bag module 

connector C-305 in the arrow direction shown, and 
disconnect the connector.

(3) 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.
(4) Insert special tool MB991866 into clock spring side of 

driver’s air bag module connector C-305 (terminal No.1 and 
2 ) by testprobe.

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

diagnostic trouble code.

Q: Is DTC B1401  set?

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

P.52B-237

). Then go to Step 6.

AC306561AC

OUTER HOUSING OF THE DRIVER'S 
AIR BAG MODULE CONNECTOR C-305

AC306758 AB

C-305 AIR BAG
MODULE
CONNECTOR

MB991865
(DUMMY RESISTOR : 3Ω)

MB991866 (RESISTOR 
HARNESS)

(REAR VIEW)

SRS AIR BAG DIAGNOSIS

SUPPLEMENTAL RESTRAINT SYSTEM (SRS)

52B-35

STEP 4. Check the clock spring. (Using diagnostic tool 
MB991958, read the diagnostic trouble code.)
(1) Disconnect the negative battery terminal.
(2) Disconnect the clock spring connector C-307.

(3) 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.
(4) Insert special tool MB991866 into harness side of clock 

spring connector C-307 (terminal No.14 and 13 ) by 
testprobe.

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

diagnostic trouble code.

Q: Is DTC B1401  set?

YES : Go to Step 5.
NO :  Replace the clock spring (Refer to 

P.52B-237

). Then 

go to Step 6.

52DB008A

C-307 (Y)

CONNECTOR: C-307

C-307 HARNESS

SIDE CONNECTOR

CLOCK

SPRING

11

12

13

14

AC306767

C-307 CLOCK SPRING
CONNECTOR

AB

MB991865

(DUMMY RESISTOR : 3Ω)

MB991866 (RESISTOR 

HARNESS)

1112 14

13

(REAR VIEW)