Code No.1402: Driver’s Air Bag Module (1st Squib) System Fault
for Earth Circuit (Short-Circuited to Earth)
| caution |
If diagnosis code B1402 is set in the
SRS-ECU, always diagnose the CAN main bus line.
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OPERATION
- The SRS-ECU judges how severe a collision is by detecting
signals from the front impact sensors and the front air bag
analogue 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.
DIAGNOSIS CODE SET CONDITIONS
This diagnosis code is set if
there is abnormal resistance between the input terminals of the
driver’s air bag module (squib).
PROBABLE CAUSES
- Malfunction of the clock spring
- Damaged harness wires and connectors
- Short to the earth in the driver’s air bag module (squib)
harness
- Malfunction of the SRS-ECU
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STEP 1. M.U.T.-III CAN bus diagnostics
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Use the M.U.T.-III to diagnose the
CAN bus lines.
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Q.
Is the check result normal?
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 Go to Step 2
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 Repair the CAN bus
line (Refer to GROUP 54F, Diagnosis  ).
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STEP 2. Check whether the diagnosis code is
reset.
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Check again if the diagnosis code
is set.
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(1)Erase the diagnosis code.
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(2)Ignition: LOCK (OFF) position to ON
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(3)On completion, check that the diagnosis code is
not reset.
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Q.
Is the diagnosis code set?
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Go to Step 3
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There is an
intermittent malfunction such as poor engaged connector(s)
or open circuit (Refer to GROUP 00, How to Cope with
Intermittent Malfunction ).
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STEP 3. Check the driver’s air bag module
(M.U.T.-III diagnosis code).
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(1)Disconnect the negative battery
terminal.
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(2)Slide the outer housing of the
driver’ s air bag module connector C-312 in the arrow
direction shown, and disconnect the connector.
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(3)Connect special tool dummy
resistor (MB991865) to special tool resistor harness
(MB991866).
(4)
| caution |
Do not insert a test probe
into the terminal from its front side directly,
as the connector contact pressure may be
weakened.
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Insert special tool MB991866 into clock spring side
air bag module connector C-312 (terminal No.1 and 2) by
backprobing.
(5)Connect the negative battery
terminal.
(6)Erase the diagnosis code memory, and check
the diagnosis code.
Q.
Is the checked diagnosis code set?
Go to Step 4
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Replace the
driver’s air bag module (Refer to ). Then go
to Step 7 .
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STEP 4. Check the clock spring (M.U.T.-III diagnosis
code).
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(1)Disconnect the negative battery
terminal.
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(2)Disconnect the clock spring
connector C-309.
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(3)Connect special tool dummy
resistor (MB991865) to special tool resistor harness
(MB991866).
(4)
| caution |
Do not insert a test probe
into the terminal from its front side directly,
as the connector contact pressure may be
weakened.
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Insert special tool MB991866 into clock spring
harness side connector C-309 (terminal No.3 and 4) by
backprobing.
(5)Connect the negative battery
terminal.
(6)Erase the diagnosis code memory, and check
the diagnosis code.
Q.
Is the checked diagnosis code set?
Go to Step 5
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Replace the
clock spring (Refer to ). Then go
to Step 7 .
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STEP 5. Check the driver’s air bag module circuit.
Resistance measurement at the SRS-ECU connector
C-119.
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(1)Disconnect SRS-ECU connector
C-119.
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(2)
| danger |
To prevent the air bag from
deploying unintentionally, disconnect the clock
spring connector C-309 to short the squib
circuit.
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Disconnect the clock spring connector
C-309.
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(3)
| caution |
Do not insert a test probe
into the terminal from its front side directly,
as the connector contact pressure may be
weakened.
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Check for continuity between C-119 harness side
connector terminals 36 and 37 and body
earth.
OK: Open circuit
Q.
Is the check result normal?
Erase the
diagnosis code memory, and check the diagnosis code. If
diagnosis code B1402 sets, replace the SRS-ECU (Refer to ). Then go
to Step 6 .
Go to Step 7
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STEP 6. Check the harness for short circuit to earth
between SRS-ECU connector C-119 (terminal No.36 and 37)
and clock spring connector C-309 (terminal No.3 and
4).
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Q.
Are the harness wires between SRS-ECU connector C-119
(terminal No.36 and 37) and clock spring connector C-309
(terminal No.3 and 4) in good condition?
Go to Step 7
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Replace the
harness wires between SRS-ECU connector C-119 and clock
spring connector C-309. Then go to Step 7 .
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STEP 7. Check whether the diagnosis code is reset.
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Q.
Is diagnosis code B1402 set?
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Return to
Step 1 .
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The procedure is
complete.
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