Lexus NX: Short in Passenger Side Front Seat Cushion Squib Circuit (B1875-B1878)

Lexus NX Service Manual / Vehicle Interior / Supplemental Restraint Systems / Airbag System / Short in Passenger Side Front Seat Cushion Squib Circuit (B1875-B1878)

DESCRIPTION

The front seat cushion squib RH circuit consists of the airbag ECU assembly and the front seat cushion airbag assembly RH.

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

These DTCs are recorded when a malfunction is detected in the front seat cushion squib RH circuit.

DTC No.

Detection Item

DTC Detection Condition

Trouble Area

B1875

Short in Passenger Side Front Seat Cushion Squib Circuit

One of the following conditions is met:
  • The airbag ECU assembly receives a line short circuit signal 5 times in the front seat cushion squib RH circuit during primary check.
  • A front seat cushion airbag assembly RH malfunction.
  • An airbag ECU assembly malfunction.
  • Floor wire
  • Front seat cushion airbag assembly RH
  • Airbag ECU assembly

B1876

Open in Passenger Side Front Seat Cushion Squib Circuit

One of the following conditions is met:
  • The airbag ECU assembly receives an open circuit signal in the front seat cushion squib RH circuit for 2 seconds.
  • A front seat cushion airbag assembly RH malfunction.
  • An airbag ECU assembly malfunction.
  • Floor wire
  • Front seat cushion airbag assembly RH
  • Airbag ECU assembly

B1877

Short to GND in Passenger Side Front Seat Cushion Squib Circuit

One of the following conditions is met:
  • The airbag ECU assembly receives a short circuit to ground signal in the front seat cushion squib RH circuit for 0.5 seconds.
  • A front seat cushion airbag assembly RH malfunction.
  • An airbag ECU assembly malfunction.
  • Floor wire
  • Front seat cushion airbag assembly RH
  • Airbag ECU assembly

B1878

Short to B+ in Passenger Side Front Seat Cushion Squib Circuit

One of the following conditions is met:
  • The airbag ECU assembly receives a short circuit to B+ signal in the front seat cushion squib RH circuit for 0.5 seconds.
  • A front seat cushion airbag assembly RH malfunction.
  • An airbag ECU assembly malfunction.
  • Floor wire
  • Front seat cushion airbag assembly RH
  • 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 CUSHION AIRBAG ASSEMBLY RH

(a) Turn the power switch off.

*1

Front Seat Cushion Airbag Assembly RH

*2

Airbag ECU Assembly

*3

Connector C

*4

SST

*a

Front view of wire harness connector

(to Front Seat Cushion Airbag Assembly RH)

(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 cushion airbag assembly RH.

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

CAUTION:

Never connect the tester to the front seat cushion airbag assembly RH 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 B1875, B1876, B1877 and B1878 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 B1875, B1876, B1877 or B1878 is not output.

REPLACE FRONT SEAT CUSHION AIRBAG ASSEMBLY RH

DTC B1875, B1876, B1877 or B1878 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 cushion airbag assembly RH side) are not damaged.

OK:

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

*1

Front Seat Cushion Airbag Assembly RH

*2

Floor Wire

*3

Airbag ECU Assembly

NG

REPLACE FLOOR WIRE

OK

3.

CHECK FLOOR WIRE

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

*1

Front Seat Cushion Airbag Assembly RH

*2

Airbag ECU Assembly

*3

Floor Wire

*4

Connector C

*a

Front view of wire harness connector

(to Front Seat Cushion Airbag Assembly RH)

(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

PF1-1 (FCP-) - Body ground

Power switch on (IG)

Below 1 V

PF1-2 (FCP+) - 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

PF1-1 (FCP-) - PF1-2 (FCP+)

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

PF1-1 (FCP-) - PF1-2 (FCP+)

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

PF1-1 (FCP-) - Body ground

Always

1 MΩ or higher

PF1-2 (FCP+) - Body ground

Always

1 MΩ or higher

NG

REPLACE FLOOR WIRE

OK

4.

CHECK DTC

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

*1

Front Seat Cushion Airbag Assembly RH

*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 B1875, B1876, B1877 and B1878 may be output at this time, but they are not related to this check.

DTC B1875, B1876, B1877 or B1878 is not output.

USE SIMULATION METHOD TO CHECK

DTC B1875, B1876, B1877 or B1878 is output.

REPLACE AIRBAG ECU ASSEMBLY

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