Lexus IS250 · Service Manual RESTRAINTS

B1920/77

Diagnostic trouble codes

DESCRIPTION

The driver side rear pretensioner squib circuit consists of the center airbag sensor assembly and the rear seat outer belt assembly (driver side).
This circuit instructs the SRS to deploy when deployment conditions are met.
These DTCs are recorded when a malfunction is detected in the driver side rear pretensioner squib circuit.
DTC No.
 DTC Detection Condition
 Trouble Area
B1920/77
  1. The center airbag sensor assembly receives a line short circuit signal 5 times in the driver side rear pretensioner squib circuit during primary check.
  2. Driver side rear pretensioner squib malfunction
  3. Center airbag sensor assembly malfunction
  1. Floor wire No. 2
  2. Rear seat outer belt assembly (Driver side rear pretensioner squib)
  3. Center airbag sensor assembly
B1921/77
  1. The center airbag sensor assembly receives an open circuit signal in the driver side rear pretensioner squib circuit for 2 seconds.
  2. Driver side rear pretensioner squib malfunction
  3. Center airbag sensor assembly malfunction
  1. Floor wire No. 2
  2. Rear seat outer belt assembly (Driver side rear pretensioner squib)
  3. Center airbag sensor assembly
B1922/77
  1. The center airbag sensor assembly receives a short circuit to ground signal in the driver side rear pretensioner squib circuit for 0.5 seconds.
  2. Driver side rear pretensioner squib malfunction
  3. Center airbag sensor assembly malfunction
  1. Floor wire No. 2
  2. Rear seat outer belt assembly (Driver side rear pretensioner squib)
  3. Center airbag sensor assembly
B1923/77
  1. The center airbag sensor assembly receives a short circuit to B+ signal in the driver side rear pretensioner squib circuit for 0.5 seconds.
  2. Driver side rear pretensioner squib malfunction
  3. Center airbag sensor assembly malfunction
  1. Floor wire No. 2
  2. Rear seat outer belt assembly (Driver side rear pretensioner squib)
  3. Center airbag sensor assembly

WIRING DIAGRAM

C124552E20

INSPECTION PROCEDURE

HINT:
  1. Perform the simulation method by selecting the "check mode" (signal check) with the intelligent tester (Click here).
  2. After selecting the "check mode" (signal check), perform the simulation method by wiggling each connector of the airbag system or driving the vehicle on a city or rough road (Click here).


1. CHECK REAR SEAT OUTER BELT ASSEMBLY (DRIVER SIDE REAR PRETENSIONER SQUIB)

  1. C123632E02
    Turn the engine switch off.

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

  1. Disconnect the connectors from the rear seat outer belt assembly (driver side).

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

    CAUTION:
    Never connect a tester to the rear seat outer belt assembly (driver side rear pretensioner squib) for measurement, as this may lead to a serious injury due to airbag deployment.

    NOTICE:
    1. Do not forcibly insert the SST into the terminals of the connector when connecting.
    2. Insert straight the SST into the terminals of the connector.

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

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

  1. Clear the DTCs stored in the memory (Click here).

  1. Turn the engine switch off.

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

  1. Check for DTCs (Click here).

    OK:
    DTC B1920, B1921, B1922, B1923 or 77 is not output.

    HINT:
    Codes other than DTC B1920, B1921, B1922, B1923 and 77 may be output at this time, but they are not related to this check.



 NG
REPLACE REAR SEAT OUTER BELT ASSEMBLY (DRIVER SIDE)
OK


2. CHECK CONNECTOR

  1. Turn the engine switch off.

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

  1. Disconnect the SST from connector "C".

  1. Check that the floor wire No. 2 connector (on the rear seat outer belt assembly (driver side) side) is not damaged.

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



 NG
REPAIR OR REPLACE FLOOR WIRE NO. 2
OK


3. CHECK FLOOR WIRE NO. 2 (DRIVER SIDE REAR PRETENSIONER SQUIB CIRCUIT)

  1. C114830E05
    Disconnect the connectors from the center airbag sensor assembly.

  1. Check for a short to B+ in the circuit.

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

    2. Turn the engine switch on (IG).

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

      Standard voltage:
      LHD:
      Tester connection
      		 Condition
      		 Specified condition
      Q20-1 (RL+) - Body ground
      		 Engine switch on (IG)
      		 Below 1 V
      Q20-2 (RL-) - Body ground
      		 Engine switch on (IG)
      		 Below 1 V
      RHD:
      Tester connection
      		 Condition
      		 Specified condition
      P17-1 (RR+) - Body ground
      		 Engine switch on (IG)
      		 Below 1 V
      P17-2 (RR-) - Body ground
      		 Engine switch on (IG)
      		 Below 1 V

  1. Check for an open in the circuit.

    1. Turn the engine switch off.

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

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

      Standard resistance:
      LHD:
      Tester connection
      		 Condition
      		 Specified condition
      Q20-1 (RL+) - Q20-2 (RL-)
      		 Always
      		 Below 1 Ω
      RHD:
      Tester connection
      		 Condition
      		 Specified condition
      P17-1 (RR+) - P17-2 (RR-)
      		 Always
      		 Below 1 Ω

  1. Check for a short to ground in the circuit.

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

      Standard resistance:
      LHD:
      Tester connection
      		 Condition
      		 Specified condition
      Q20-1 (RL+) - Body ground
      		 Always
      		 1 MΩ or higher
      Q20-2 (RL-) - Body ground
      		 Always
      		 1 MΩ or higher
      RHD:
      Tester connection
      		 Condition
      		 Specified condition
      P17-1 (RR+) - Body ground
      		 Always
      		 1 MΩ or higher
      P17-2 (RR-) - Body ground
      		 Always
      		 1 MΩ or higher

  1. Check for a short in the circuit.

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

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

      Standard resistance:
      LHD:
      Tester connection
      		 Condition
      		 Specified condition
      Q20-1 (RL+) - Q20-2 (RL-)
      		 Always
      		 1 MΩ or higher
      RHD:
      Tester connection
      		 Condition
      		 Specified condition
      P17-1 (RR+) - P17-2 (RR-)
      		 Always
      		 1 MΩ or higher



NG
REPAIR OR REPLACE FLOOR WIRE NO. 2
OK


4. CHECK CENTER AIRBAG SENSOR ASSEMBLY

  1. C123633E01
    Connect the connectors to the rear seat outer belt assembly (driver side) and the center airbag sensor assembly.

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

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

  1. Clear the DTCs stored in the memory (Click here).

  1. Turn the engine switch off.

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

  1. Check for DTCs (Click here).

    OK:
    DTC B1920, B1921, B1922, B1923 or 77 is not output.

    HINT:
    Codes other than B1920, B1921, B1922, B1923 and 77 may be output at this time, but they are not related to this check.



 NG
REPLACE CENTER AIRBAG SENSOR ASSEMBLY
OK

USE SIMULATION METHOD TO CHECK


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