Lexus RX (RX 350L, RX450h) 2016-2024 Repair Manual: Short in Passenger Side Front Seat Cushion Squib Circuit (B1875-B1878)

DESCRIPTION

The passenger side front seat cushion squib circuit consists of the airbag sensor assembly and front seat cushion airbag assembly RH.

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

These DTCs are stored when a malfunction is detected in the passenger side front seat cushion squib circuit.

DTC No.	Detection Item	DTC Detection Condition	Trouble Area	Warning Indicate	Test Mode / Check Mode
B1875	Short in Passenger Side Front Seat Cushion Squib Circuit	The airbag sensor assembly detects a line short in the passenger side front seat cushion squib circuit during the primary check. Passenger side front seat cushion squib malfunction Airbag sensor assembly malfunction	Floor wire Passenger side front seat cushion squib (Front seat cushion airbag assembly RH) Airbag sensor assembly	Comes on	Applies to check mode
B1876	Open in Passenger Side Front Seat Cushion Squib Circuit	The airbag sensor assembly detects an open in the passenger side front seat cushion squib circuit. Passenger side front seat cushion squib malfunction Airbag sensor assembly malfunction	Floor wire Passenger side front seat cushion squib (Front seat cushion airbag assembly RH) Airbag sensor assembly	Comes on	Applies to check mode
B1877	Short to GND in Passenger Side Front Seat Cushion Squib Circuit	The airbag sensor assembly detects a short to ground in the passenger side front seat cushion squib circuit. Passenger side front seat cushion squib malfunction Airbag sensor assembly malfunction	Floor wire Passenger side front seat cushion squib (Front seat cushion airbag assembly RH) Airbag sensor assembly	Comes on	Applies to check mode
B1878	Short to B+ in Passenger Side Front Seat Cushion Squib Circuit	The airbag sensor assembly detects a short to B+ in the passenger side front seat cushion squib circuit. Passenger side front seat cushion squib malfunction Airbag sensor assembly malfunction	Floor wire Passenger side front seat cushion squib (Front seat cushion airbag assembly RH) 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.

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PROCEDURE

1.	CHECK CONNECTORS

(a) Turn the engine switch off.

*1 Front Seat Cushion Airbag Assembly RH *2 Airbag Sensor Assembly *3 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 cushion airbag assembly RH 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 cushion airbag assembly RH 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 short springs of the activation prevention mechanism of the floor wire connector are not deformed or damaged.

OK:

The short springs are not deformed or damaged.

NG

REPLACE FLOOR WIRE

OK

2.	CHECK FRONT SEAT CUSHION AIRBAG ASSEMBLY RH

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

*1 Front Seat Cushion Airbag Assembly RH *2 Airbag Sensor Assembly *a Front view of wire harness connector (to Front Seat Cushion Airbag Assembly RH)

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

CAUTION:

Never connect a tester to the front seat cushion airbag assembly RH for measurement, as this may lead to a serious injury due to airbag 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 B1875, B1876, B1877 or B1878 is not output.

HINT:

Codes other than DTCs B1875, B1876, B1877 and B1878 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 CUSHION AIRBAG ASSEMBLY RH

NG

3.	CHECK FLOOR WIRE

(a) Disconnect the floor wire from the airbag sensor assembly.

*1 Front Seat Cushion Airbag Assembly RH *2 Airbag Sensor Assembly *3 Floor Wire *a Front view of wire harness connector (to Front Seat Cushion Airbag Assembly RH)

(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
R21-1 (FCP+) - Body ground	Engine switch on (IG)	Below 1 V
R21-2 (FCP-) - 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
R21-1 (FCP+) - R21-2 (FCP-)	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
R21-1 (FCP+) - Body ground	Always	1 MΩ or higher
R21-2 (FCP-) - 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
R21-1 (FCP+) - R21-2 (FCP-)	Always	1 MΩ or higher

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

NG

REPLACE FLOOR WIRE

OK

4.

CHECK DTC

(a) Connect the connectors to the front seat cushion airbag assembly RH and airbag sensor assembly.

*1 Front Seat Cushion Airbag Assembly RH *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 B1875, B1876, B1877 or B1878 is not output.

HINT:

Codes other than DTCs B1875, B1876, B1877 and B1878 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