Lexus NX manuals

Lexus NX: Short in P/T Squib (LH) Circuit (B1905-B1908)

Lexus NX Service Manual / Vehicle Interior / Supplemental Restraint Systems / Airbag System / Short in P/T Squib (LH) Circuit (B1905-B1908)

DESCRIPTION

The front pretensioner LH circuit consists of the airbag ECU assembly and front seat outer belt assembly LH.

This circuit instructs the SRS to deploy when deployment conditions are met.

These DTCs are stored when a malfunction is detected in the front pretensioner LH circuit.

DTC No.

Detection Item

DTC Detection Condition

Trouble Area

B1905

Short in P/T Squib (LH) Circuit

One of the following conditions is met:

  • The airbag ECU assembly detects a line short circuit signal 5 times in the front pretensioner LH circuit during the primary check.
  • A front seat outer belt assembly LH malfunction.
  • An airbag ECU assembly malfunction.
  • No. 2 floor wire
  • Front seat outer belt assembly LH
  • Airbag ECU assembly

B1906

Open in P/T Squib (LH) Circuit

One of the following conditions is met:

  • The airbag ECU assembly detects an open circuit signal in the front pretensioner LH circuit for 2 seconds.
  • A front seat outer belt assembly LH malfunction.
  • An airbag ECU assembly malfunction.
  • No. 2 floor wire
  • Front seat outer belt assembly LH
  • Airbag ECU assembly

B1907

Short in P/T Squib (LH) Circuit (to Ground)

One of the following conditions is met:

  • The airbag ECU assembly detects a short circuit to ground signal in the front pretensioner LH circuit for 0.5 seconds.
  • A front seat outer belt assembly LH malfunction.
  • An airbag ECU assembly malfunction.
  • No. 2 floor wire
  • Front seat outer belt assembly LH
  • Airbag ECU assembly

B1908

Short in P/T Squib (LH) Circuit (to +B)

One of the following conditions is met:

  • The airbag ECU assembly detects a short circuit to B+ signal in the front pretensioner LH circuit for 0.5 seconds.
  • A front seat outer belt assembly LH malfunction.
  • An airbag ECU assembly malfunction.
  • No. 2 floor wire
  • Front seat outer belt assembly LH
  • Airbag ECU assembly

WIRING DIAGRAM

CAUTION / NOTICE / HINT

NOTICE:

  • After the power switch is turned off, there may be a waiting time before disconnecting the negative (-) auxiliary battery terminal.

    Click here

  • When disconnecting and reconnecting the auxiliary battery

    Click here

    HINT:

    When disconnecting and reconnecting the auxiliary battery, there is an automatic learning function that completes learning when the respective system is used.

    Click here

  • After replacing the airbag ECU assembly, refer to initialization.

    Click here

HINT:

To perform the simulation method, enter check mode (signal check) with the Techstream (Click here ), and then wiggle each connector of the airbag system or drive the vehicle on various types of road (Click here ).

PROCEDURE

1.

CHECK FRONT SEAT OUTER BELT ASSEMBLY LH

(a) Turn the power switch off.

*1

Front Seat Outer Belt Assembly LH

*2

Airbag ECU Assembly

*3

Connector C

*4

SST

*a

Front view of wire harness connector

(to Front Seat Outer Belt Assembly LH)

(b) Disconnect the cable from the negative (-) auxiliary battery terminal, and wait for at least 90 seconds.

(c) Disconnect the connector from the front seat outer belt assembly LH.

(d) Connect the white wire side of SST (resistance: 2.1 Ω) to connector C.

CAUTION:

Never connect the tester to the front seat outer belt assembly LH for measurement, as this may lead to a serious injury due to airbag deployment.

NOTICE:

  • Do not forcibly insert SST into the terminals of the connector when connecting SST.
  • Insert SST straight into the terminals of the connector.

SST: 09843-18061

(e) Connect the cable to the negative (-) auxiliary battery terminal, and wait for at least 2 seconds.

(f) Turn the power switch on (IG), and wait for at least 60 seconds.

(g) Clear the DTCs.

Click here

Body Electrical > SRS Airbag > Clear DTCs

(h) Turn the power switch off.

(i) Turn the power switch on (IG), and wait for at least 60 seconds.

(j) Check for DTCs.

Click here

Body Electrical > SRS Airbag > Trouble Codes

HINT:

Codes other than DTC B1905, B1906, B1907 and B1908 may be output at this time, but they are not related to this check.

(k) Turn the power switch off.

(l) Disconnect the cable from the negative (-) auxiliary battery terminal, and wait for at least 90 seconds.

(m) Disconnect SST from connector C.

DTC B1905, B1906, B1907 or B1908 is not output

REPLACE FRONT SEAT OUTER BELT ASSEMBLY LH

DTC B1905, B1906, B1907 or B1908 is output

2.

CHECK CONNECTORS

(a) Disconnect the connectors from the airbag ECU assembly.

(b) Check that the connectors (on the airbag ECU assembly side and front seat outer belt assembly LH side) are not damaged.

OK:

The lock button is not disengaged, and the claw of the lock is not deformed or damaged.

*1

Front Seat Outer Belt Assembly LH

*2

No. 2 Floor Wire

*3

Airbag ECU Assembly
NG

REPLACE NO. 2 FLOOR WIRE
OK

3.

CHECK NO. 2 FLOOR WIRE

(a) Connect the cable to the negative (-) auxiliary battery terminal, and wait for at least 2 seconds.

*1

Front Seat Outer Belt Assembly LH

*2

No. 2 Floor Wire

*3

Airbag ECU Assembly

*4

Connector C

*a

Front view of wire harness connector

(to Front Seat Outer Belt Assembly LH)

(b) Turn the power switch on (IG).

(c) Measure the voltage according to the value(s) in the table below.

Standard Voltage:

Tester Connection

Switch Condition

Specified Condition

Q4-1 (L-) - Body ground

Power switch on (IG)

Below 1 V

Q4-2 (L+) - Body ground

Power switch on (IG)

Below 1 V

(d) Turn the power switch off.

(e) Disconnect the cable from the negative (-) auxiliary battery terminal, and wait for at least 90 seconds.

(f) Measure the resistance according to the value(s) in the table below.

Standard Resistance:

Tester Connection

Condition

Specified Condition

Q4-1 (L-) - Q4-2 (L+)

Always

Below 1 Ω

(g) Release the activation prevention mechanism built into connector B.

Click here

(h) Measure the resistance according to the value(s) in the table below.

Standard Resistance:

Tester Connection

Condition

Specified Condition

Q4-1 (L-) - Q4-2 (L+)

Always

1 MΩ or higher

(i) Restore the released activation prevention mechanism of connector B to its original condition.

(j) Measure the resistance according to the value(s) in the table below.

Standard Resistance:

Tester Connection

Condition

Specified Condition

Q4-1 (L-) - Body ground

Always

1 MΩ or higher

Q4-2 (L+) - Body ground

Always

1 MΩ or higher
NG

REPLACE NO. 2 FLOOR WIRE
OK

4.

CHECK DTC

(a) Connect the connectors to the front seat outer belt assembly LH and airbag ECU assembly.

*1

Front Seat Outer Belt Assembly LH

*2

Airbag ECU Assembly

(b) Connect the cable to the negative (-) auxiliary battery terminal, and wait for at least 2 seconds.

(c) Turn the power switch on (IG), and wait for at least 60 seconds.

(d) Clear the DTCs.

Click here

Body Electrical > SRS Airbag > Clear DTCs

(e) Turn the power switch off.

(f) Turn the power switch on (IG), and wait for at least 60 seconds.

(g) Check for DTCs.

Click here

Body Electrical > SRS Airbag > Trouble Codes

HINT:

Codes other than DTC B1905, B1906, B1907 and B1908 may be output at this time, but they are not related to this check.

DTC B1905, B1906, B1907 or B1908 is not output

USE SIMULATION METHOD TO CHECK

DTC B1905, B1906, B1907 or B1908 is output

REPLACE AIRBAG ECU ASSEMBLY

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