Mitsubishi 380. Manual - part 779

SRS AIR BAG DIAGNOSIS

SUPPLEMENTAL RESTRAINT SYSTEM (SRS)

52B-40

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 clock spring harness side 

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

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

diagnostic trouble code.

Q:  Is DTC B1402  set?

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

P.52B-237

). Then 

go to Step 7.

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)

SRS AIR BAG DIAGNOSIS

SUPPLEMENTAL RESTRAINT SYSTEM (SRS)

52B-41

STEP 5. Check the driver’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 clock spring connector C-307 to short 
the squib circuit.

(2) Disconnect the clock spring connector C-307.
(3) 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.
(4) Measure the voltage between C-121 harness side 

connector terminals 28 and 27  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 B1402  sets, 
replace the SRS-ECU (Refer to 

P.52B-234

). Then go 

to Step 7.

NO :  Go to Step 6.

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)

52DB008A

C-307 (Y)

CONNECTOR: C-307

C-307 HARNESS

SIDE CONNECTOR

CLOCK

SPRING

11

12

13

14

SRS AIR BAG DIAGNOSIS

SUPPLEMENTAL RESTRAINT SYSTEM (SRS)

52B-42

STEP 6. Check the harness for short circuit to power 
supply between SRS-ECU connector C-121 (terminal No.28 
and 27 ) and clock spring connector C-307 (terminal No.13 
and 14).
Q: Are harness wires between the SRS-ECU connector 

C-121 (terminal No.28 and 27 ) and clock spring 
connector C-307 (terminal No.13 and 14) in good 
condition?
YES : Go to Step 7.
NO :  Replace the harness wires between SRS-ECU 

connector C-121 and clock spring connector C-307. 
Then go to Step 7.

STEP 7. 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 B1402  set?

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

52DB008A

C-307 (Y)

CONNECTOR: C-307

C-307 HARNESS

SIDE CONNECTOR

CLOCK

SPRING

11

12

13

14

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)

00DB076A

MB991910

DATA LINK

CONNECTOR

MB991824

MB991827

SRS AIR BAG DIAGNOSIS

SUPPLEMENTAL RESTRAINT SYSTEM (SRS)

52B-43

DTC 1403: Driver’s Air Bag Module (1st Squib) System Fault for Ground Circuit (Short-Circuited to 
Ground)

CAUTION

If DTC B1403  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 sent 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 air bag 
module (squib). However, if no DTC resets, 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

• Malfunction of the clock spring

• Damaged harness wires and connectors

• Short to the ground in the driver's air bag module 

(squib) harness

• 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)