Mitsubishi 380. Manual — part 775
SRS AIR BAG DIAGNOSIS
SUPPLEMENTAL RESTRAINT SYSTEM (SRS)
52B-24
DIAGNOSTIC TROUBLE CODE PROCEDURES
DTC B1400: Driver’s Air Bag Module (1st Squib) System Fault 1 (Short Circuit between Terminals of
the Squib Circuit)
CAUTION
If DTC B1400 or B1480 <2nd squib> is set in the
combination meter, always diagnose the CAN
bus lines.
.
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:
• Short circuit in driver’s air bag module (squib)
or harness
• Short circuit in the clock spring
However, if no DTC reset, the SRS warning light will
be turned off (DTC will OK).
.
TROUBLESHOOTING HINTS
• Refer to circuit diagrams GROUP-
• Refer to configuration diagrams GROUP-
• Improper engaged connector or defective short
spring*
• Short circuit in the clock spring
• Short circuit between the driver's air bag module
(squib) circuit terminals
• Damaged connector(s)
• Malfunction of the SRS-ECU
.
NOTE: *: The squib circuit connectors integrate a
"short" spring (which prevents the air bag from
deploying unintentionally due to static electricity by
shorting the positive wire to the ground wire in the
squib circuit when the connectors are disconnected)
(Refer to
). Therefore, if connector C-121, ,
C-307 or C-305 is damaged or improperly engaged,
the short spring may not be released when the con-
nector is connected.
.
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-25
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
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
."
(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 ).
00DB076A
MB991910
DATA LINK
CONNECTOR
MB991824
MB991827
SRS AIR BAG DIAGNOSIS
SUPPLEMENTAL RESTRAINT SYSTEM (SRS)
52B-26
STEP 2. Recheck for diagnostic trouble code.
Check again if the DTC is set.
(1) Erase the DTC.
(2) Turn the ignition switch to "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 ).
STEP 3. Using diagnostic tool MB991958, read the
diagnostic trouble code.
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) Turn the ignition switch to the "ON" position.
(2) Check if the DTC is set.
(3) Turn the ignition switch to the "LOOK (OFF)" position.
Q: Is DTC B1519 set?
YES : Go to Step 4.
NO : Go to Step 5.
00DB076A
MB991910
DATA LINK
CONNECTOR
MB991824
MB991827
00DB076A
MB991910
DATA LINK
CONNECTOR
MB991824
MB991827
SRS AIR BAG DIAGNOSIS
SUPPLEMENTAL RESTRAINT SYSTEM (SRS)
52B-27
STEP 4. Check SRS-ECU connector C-121.
Q: Is the connector correctly engaged?
YES : Go to Step 5.
NO : Engage the connector correctly. Then go to Step 10.
STEP 5. Check SRS-ECU connector C-121, clock spring
connector C-307 and driver’s air bag module connector
C-305. (Using diagnostic tool MB991958, read the
diagnostic trouble code.)
(1) Disconnect the negative battery terminal.
(2) Disconnect connectors C-121, C-307 and C-305, and then
reconnect them.
(3) Connect the negative battery terminal.
(4) Erase the diagnostic trouble code memory, and check the
diagnostic trouble code.
Q: Is DTC B1400 set?
YES : Go to Step 6.
NO : The procedure is complete. It is assumed that DTC
B1400 set because connector C-121, C-307 or C-305
was engaged improperly.
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)
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)
52DB007A
C-307 (Y)
CONNECTORS: C-305, C-307
CLOCK
SPRING
11
12
13
14
C-307 HARNESS
SIDE CONNECTOR
C-305 (Y)
C-305 HARNESS
SIDE CONNECTOR
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