Lexus RX (RX 350L, RX450h) 2016-2025 Repair Manual: Short in P/T Squib (LH) Circuit (B1905-B1908)

DESCRIPTION

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

The airbag sensor assembly uses this circuit to deploy the pretensioner when deployment conditions are met.

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

DTC No.	Detection Item	DTC Detection Condition	Trouble Area	Warning Indicate	Test Mode / Check Mode
B1905	Short in P/T Squib (LH) Circuit	The airbag sensor assembly detects a line short in the front pretensioner squib LH circuit during the primary check. Front pretensioner squib LH malfunction Airbag sensor assembly malfunction	No. 2 floor wire Front pretensioner squib LH (Front seat outer belt assembly LH) Airbag sensor assembly	Comes on	Applies to check mode
B1906	Open in P/T Squib (LH) Circuit	The airbag sensor assembly detects an open in the front pretensioner squib LH circuit. Front pretensioner squib LH malfunction Airbag sensor assembly malfunction	No. 2 floor wire Front pretensioner squib LH (Front seat outer belt assembly LH) Airbag sensor assembly	Comes on	Applies to check mode
B1907	Short in P/T Squib (LH) Circuit (to Ground)	The airbag sensor assembly detects a short to ground in the front pretensioner squib LH circuit. Front pretensioner squib LH malfunction Airbag sensor assembly malfunction	No. 2 floor wire Front pretensioner squib LH (Front seat outer belt assembly LH) Airbag sensor assembly	Comes on	Applies to check mode
B1908	Short in P/T Squib (LH) Circuit (to +B)	The airbag sensor assembly detects a short to B+ in the front pretensioner squib LH circuit. Front pretensioner squib LH malfunction Airbag sensor assembly malfunction	No. 2 floor wire Front pretensioner squib LH (Front seat outer belt assembly LH) Airbag sensor assembly	Comes on	Applies to check mode

WIRING DIAGRAM

CAUTION / NOTICE / HINT

NOTICE:

After turning the engine switch off, waiting time may be required before disconnecting the cable from the negative (-) battery terminal. Therefore, make sure to read the disconnecting the cable from the negative (-) battery terminal notices before proceeding with work.

Click here

PROCEDURE

1.	CHECK CONNECTORS

(a) Turn the engine switch off.

*1 Front Seat Outer Belt Assembly LH *2 Airbag Sensor Assembly *3 No. 2 Floor Wire

(b) Disconnect the cable from the negative (-) battery terminal.

CAUTION:

Wait at least 90 seconds after disconnecting the cable from the negative (-) battery terminal to disable the SRS system.

(c) Check that the connectors are properly connected to the front seat outer belt assembly LH and airbag sensor assembly.

OK:

The connectors are properly connected.

HINT:

If the connectors are not properly connected, reconnect the connectors and proceed to the next inspection.

(d) Disconnect the connectors from the front seat outer belt assembly LH and airbag sensor assembly.

(e) Check that the terminals of the connectors are not deformed or damaged.

OK:

The terminals are not deformed or damaged.

(f) Check that the No. 2 floor wire connector (on the front seat outer belt assembly LH side) is not loose, deformed or damaged.

OK:

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

(g) Check that the short springs of the activation prevention mechanism of the No. 2 floor wire connector are not deformed or damaged.

OK:

The short springs are not deformed or damaged.

NG

REPLACE NO. 2 FLOOR WIRE

OK

2.	CHECK FRONT SEAT OUTER BELT ASSEMBLY LH

(a) Connect the connector to the airbag sensor assembly.

*1 Front Seat Outer Belt Assembly LH *2 Airbag Sensor Assembly *a Front view of wire harness connector (to Front Seat Outer Belt Assembly LH)

(b) Connect SST (resistance 2.1 Ω) to connector C.

CAUTION:

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

SST: 09843-18061

(c) Connect the cable to the negative (-) battery terminal.

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

(e) Clear the DTCs stored in memory.

Body Electrical > SRS Airbag > Clear DTCs

(f) Turn the engine switch off.

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

(h) Check for DTCs.

Body Electrical > SRS Airbag > Trouble Codes

OK:

DTC B1905, B1906, B1907 or B1908 is not output.

HINT:

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

(i) Turn the engine switch off.

(j) Disconnect the cable from the negative (-) battery terminal.

CAUTION:

Wait at least 90 seconds after disconnecting the cable from the negative (-) battery terminal to disable the SRS system.

(k) Disconnect SST from connector C.

OK

REPLACE FRONT SEAT OUTER BELT ASSEMBLY LH

NG

3.	CHECK NO. 2 FLOOR WIRE

(a) Disconnect the No. 2 floor wire from the airbag sensor assembly.

*1 Front Seat Outer Belt Assembly LH *2 Airbag Sensor Assembly *3 No. 2 Floor Wire *a Front view of wire harness connector (to Front Seat Outer Belt Assembly LH)

(b) Check for a short to B+ in the circuit.

(1) Connect the cable to the negative (-) battery terminal.

(2) Turn the engine switch on (IG).

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

Standard Voltage:

Tester Connection	Condition	Specified Condition
S4-1 (L+) - Body ground	Engine switch on (IG)	Below 1 V
S4-2 (L-) - Body ground	Engine switch on (IG)	Below 1 V

(4) Turn the engine switch off.

(5) Disconnect the cable from the negative (-) battery terminal.

CAUTION:

Wait at least 90 seconds after disconnecting the cable from the negative (-) battery terminal to disable the SRS system.

(c) Check for an open in the circuit.

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

Standard Resistance:

Tester Connection	Condition	Specified Condition
S4-1 (L+) - S4-2 (L-)	Always	Below 1 Ω

(d) Check for a short to ground in the circuit.

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

Standard Resistance:

Tester Connection	Condition	Specified Condition
S4-1 (L+) - Body ground	Always	1 MΩ or higher
S4-2 (L-) - Body ground	Always	1 MΩ or higher

(e) Check for a short in the circuit.

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

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

Standard Resistance:

Tester Connection	Condition	Specified Condition
S4-1 (L+) - S4-2 (L-)	Always	1 MΩ or higher

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

NG

REPLACE NO. 2 FLOOR WIRE

OK

4.

CHECK DTC

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

*1 Front Seat Outer Belt Assembly LH *2 Airbag Sensor Assembly

(b) Connect the cable to the negative (-) battery terminal.

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

(d) Clear the DTCs stored in memory.

Body Electrical > SRS Airbag > Clear DTCs

(e) Turn the engine switch off.

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

(g) Check for DTCs.

Body Electrical > SRS Airbag > Trouble Codes

OK:

DTC B1905, B1906, B1907 or B1908 is not output.

HINT:

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

OK

USE SIMULATION METHOD TO CHECK

NG

REPLACE AIRBAG SENSOR ASSEMBLY