Code No.B1401:
Driver’s air bag module (squib) system (open-circuited in the squib circuit)
OPERATION
Only when the frontal impact exceeding the threshold is simultaneously detected (turned
ON) by the front impact sensor as well as by the analog G-sensor and safing G-sensor in SRS-ECU,
the electric current is supplied from SRS-ECU to the driver’s air bag module (squib).
TROUBLE JUDGEMENT
The code is set when the open circuit occurs to the SRS-ECU driver’s air bag
module (squib) circuit.
PROBABLE CAUSES
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) connector
Improper connector contact
Malfunction of the SRS-ECU
DIAGNOSIS PROCEDURE
STEP 1. Check the diagnosis code by connecting a dummy resistor.
(1)Check that the negative auxiliary battery terminal is disconnected. If the negative
auxiliary battery terminal is connected, disconnect it.
(2)By sliding the A section (in the figure) of the B-207 air bag module connector 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 the B-205 clock spring side air bag module connector
by backprobing. (5)Connect the negative auxiliary battery terminal. (6)After erasing the diagnosis code memory, check the diagnosis code again. (7)Disconnect the negative auxiliary battery terminal.
Q.
Is diagnosis code B1401 set?
Go to Step 2
Replace the driver’s air bag module (Refer to ).
STEP 2. Diagnosis check by dummy resistor connection.
(1)Check that the negative auxiliary battery terminal is disconnected. If the negative
auxiliary battery terminal is connected, disconnect it.
(2)Disconnect the B-205 clock spring 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 the B-205 clock spring harness side connector (terminal
No.13 and 14) by backprobing. (5)Connect the negative auxiliary battery terminal. (6)After erasing the diagnosis code memory, check the diagnosis code again. (7)Disconnect the negative auxiliary battery terminal.
Q.
Is diagnosis code B1401 set?
Go to Step 3
Replace the clock spring (Refer to ).
STEP 3. Resistance measurement at the B-112 SRS-ECU and the B-205
clock spring connector.
(1)Check that the negative auxiliary battery terminal is disconnected. If the negative
auxiliary battery terminal is connected, disconnect it.
(2)Disconnect the B-112 SRS-ECU connector.
(3)
danger
To release SRS-ECU connector short spring in the following
operations, disconnect this clock spring connector, and keep the squib circuit shorted.
Disconnect the B-205 clock spring connector.
(4)
caution
The short spring may not be released due to the insufficient insertion. Therefore, insert
the insulator for 4 mm or more.
Insert the insulator (width: 3 mm, thickness: 0.5 mm) such as cable tie between the terminals
Nos. 27 and 28, and then 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.
Take the measurements below at the B-112 and B-205 harness side connectors.
Continuity between B-112 SRS-ECU connector terminal No.
27 and B-205 clock spring connector terminal No. 13
Continuity between the B-112 SRS-ECU connector terminal No. 28 and B-205 clock spring
connector terminal No. 14
OK: Continuity (Less than 2 Ω)
Q.
Is the check result normal?
Go to Step 4
Repair the wiring harnesses between the B-205 clock spring connector (terminal
No.13 and 14) and the B-112 SRS-ECU connector (terminal No.27 and 28).
STEP 4. Check whether the diagnosis code is reset.
Q.
Is diagnosis code B1401 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
Replace the driver’s air bag module (Refer to 
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