Code No.B1400:
Driver’s air bag module (squib) system (short-circuited between terminals of the squib
circuit)
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 input to the air bag module via the clock spring to inflate
the air bag.
DIAGNOSIS CODE SET CONDITIONS
This diagnosis code is set if one driver’s air bag squib wire shorted to the
other. PROBABLE CAUSES
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 earth wire in the squib circuit when the connectors are disconnected). Therefore, if
connector C-154, C-303 or C-305 is damaged or improperly engaged, the short spring may not be
released when the connector is connected.
(2)Disconnect connectors C-154 and then reconnect them. (3)Connect the negative battery terminal. (4)Erase the diagnosis code memory, and check the diagnosis code.
Q.
Is diagnosis code B1400 set?
Go to Step 3.
The procedure is complete. It is assumed that diagnosis code B1400 set as connector
C-154 was engaged improperly.
STEP 3. Connector lock check: SRS-ECU connector C-154, clock spring
connector C-305 and driver’s air bag module connector C-303. (M.U.T.-III diagnosis
code)
(1)Disconnect the negative battery terminal.
(2)Disconnect connectors C-154, C-305 and C-303, and then reconnect them. (3)Connect the negative battery terminal. (4)Erase the diagnosis code memory, and check the diagnosis code.
Q.
Is diagnosis code B1400 set?
Go to Step 4.
The procedure is complete. It is assumed that diagnosis code B1400 set as connector
C-154, C-305 or C-303 was engaged improperly.
STEP 4. Check the diagnosis code by connecting a dummy resistor. (M.U.T.-III
diagnosis code)
(1)Disconnect the negative battery terminal.
(2)By sliding the A section (in the figure) of air bag module connector C-303 in the arrow
direction, disconnect the connector.
(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.
Insert special tool (MB991866) into clock spring side air bag module connector C-303 by backprobing. (5)Connect the negative battery terminal. (6)Erase the diagnosis code memory, and check the diagnosis code.
Q.
Is diagnosis code B1400 set?
Go to Step 5.
Replace the driver’s air bag module (Refer to ).
STEP 5. Check the diagnosis code by connecting a dummy resistor. (M.U.T.-III
diagnosis code)
(1)Disconnect the negative battery terminal.
(2)Disconnect the clock spring connector C-305. (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.
Insert special tool (MB991866) into clock spring harness side connector C-305 (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 diagnosis code B1400 set?
Go to Step 6.
Replace the clock spring (Refer to ).
STEP 6. Resistance measurement at the SRS-ECU connector C-154.
(1)Disconnect the negative battery terminal.
(2)Disconnect SRS-ECU connector C-154.
(3)
danger
To prevents the air bag from deploying unintentionally, disconnect the clock spring connector
C-305 to short the squib circuit.
Disconnect the clock spring connector C-305.
(4)
caution
Insert an insulator such as a cable tie to a depth of 7 mm or more, otherwise the short
spring will not be released.
Insert a cable tie [3 mm wide, 0.5 mm thick] between terminals 27, 28
and the short spring to release the short spring.
(5)
caution
Do not insert a test probe into the terminal from its front side directly as the connector contact
pressure may be weakened.
Resistance measurement between C-154 harness side connector terminals 27 and 28. OK: Open circuit
Q.
Is the check result normal?
Go to Step 7.
Repair the harness wires between SRS-ECU connector C-154 (terminal No.27 and 28)
and clock spring connector C-305 (terminal No.3 and 4).
STEP 7. Check whether the diagnosis code is reset.
Q.
Is diagnosis code B1400 set?
Replace the SRS-ECU (Refer to ).
An intermittent malfunction is suspected (Refer to GROUP 00, How to Cope with
Intermittent Malfunction ).
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Go to Step 2.
Go to Step 3.)
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