Lexus NX manuals

Lexus NX: Center Airbag Sensor Assembly Communication Circuit Malfunction (B1790)

Lexus NX Service Manual / Vehicle Interior / Supplemental Restraint Systems / Occupant Classification System / Center Airbag Sensor Assembly Communication Circuit Malfunction (B1790)

DESCRIPTION

The airbag ECU assembly communication circuit consists of the occupant detection ECU and airbag ECU assembly.

DTC B1790 is stored when a malfunction is detected in the airbag ECU assembly communication circuit.

DTC No.

Detection Item

DTC Detection Condition

Trouble Area

B1790

Center Airbag Sensor Assembly Communication Circuit Malfunction
One of the following conditions is met:
  • Occupant detection ECU detects a line short circuit signal, open circuit signal, short circuit to ground signal or short circuit to +B signal in the airbag ECU assembly communication circuit for 2 seconds.
  • Airbag ECU assembly malfunction.
  • Occupant detection ECU malfunction.
  • Floor wire
  • Front seat wire RH
  • Occupant detection ECU
  • Airbag ECU assembly

HINT:

  • When DTC B1650/32 is stored as a result of troubleshooting the airbag system, perform troubleshooting for DTC B1790 of the occupant classification system.
  • Use the Techstream to check for DTCs of the occupant detection ECU, otherwise the DTCs cannot be read.

WIRING DIAGRAM

CAUTION / NOTICE / HINT

NOTICE:

  • After turning the engine switch off, waiting time may be required before disconnecting the cable from the negative (-) auxiliary battery terminal.

    Click here

  • When disconnecting and reconnecting the auxiliary battery

    Click here

    HINT:

    When disconnecting and reconnecting the 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:

  • If troubleshooting (wire harness inspection) is difficult to perform, remove the front RH seat installation bolts to see the undersurface of the seat cushion.
  • In the above case, hold the seat so that it does not fall down. Holding the seat for a long period of time may cause problems, such as seat rail deformation. Hold the seat up only for as long as necessary.

PROCEDURE

1.

CHECK DTC

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

(b) Clear the DTCs.

Click here

Body Electrical > Occupant Detection > Clear DTCs

HINT:

  • First clear the DTCs stored in the occupant detection ECU, and then clear the DTCs stored in the airbag ECU assembly.
  • Use the Techstream to clear the DTCs of the occupant detection ECU, otherwise the DTCs cannot be cleared.

(c) Turn the power switch off.

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

(e) Check for DTCs.

Click here

Body Electrical > Occupant Detection > Trouble Codes

HINT:

DTCs other than DTC B1790 may be output at this time, but they are not related to this check.

DTC B1790 is not output

USE SIMULATION METHOD TO CHECK

DTC B1790 is output

2.

CHECK CONNECTION OF CONNECTORS

(a) Turn the power switch off.

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

(c) Check that the connectors are properly connected to the occupant detection ECU and airbag ECU assembly.

Connectors are not properly connected

CONNECT CONNECTOR
Connectors are properly connected

3.

CHECK CONNECTORS

(a) Disconnect the connectors from the airbag ECU assembly and occupant detection ECU.

*1

Occupant Detection ECU

*2

Airbag ECU Assembly

(b) Check that the connectors (on the airbag ECU assembly side and occupant detection ECU side) are not damaged.

Connectors are deformed or damaged

REPLACE HARNESS AND CONNECTOR
Connectors are not deformed or damaged

4.

CHECK AIRBAG ECU ASSEMBLY CIRCUIT

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

*1

Occupant Detection ECU

*2

Airbag ECU Assembly

*3

Connector E

*4

Connector B

*5

Service Wire

*a

Front view of wire harness connector

(to Occupant Detection ECU)

*b

Rear view of wire harness connector

(to Airbag ECU Assembly)

(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

f15-7 (FSR+) - Body ground

Power switch on (IG)

Below 1 V

f15-4 (FSR-) - Body ground

(d) Turn the power switch off.

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

(f) Using a service wire, connect terminals 9 (FSR+) and 17 (FSR-) of connector B.

NOTICE:

Do not forcibly insert the service wire into the terminals of the connector.

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

Standard Resistance:

Tester Connection

Condition

Specified Condition

f15-7 (FSR+) - f15-4 (FSR-)

Always

Below 1 Ω

(h) Disconnect the service wire from connector B.

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

Standard Resistance:

Tester Connection

Condition

Specified Condition

f15-7 (FSR+) - f15-4 (FSR-)

Always

1 MΩ or higher

f15-7 (FSR+) - Body ground

f15-4 (FSR-) - Body ground
NG

GO TO STEP 10

OK

5.

CHECK DTC

(a) Connect the connectors to the occupant detection ECU and 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 > Occupant Detection > Clear DTCs

HINT:

  • First clear the DTCs stored in the occupant detection ECU, and then clear the DTCs stored in the airbag ECU assembly.
  • Use the Techstream to clear the DTCs of the occupant detection ECU, otherwise the DTCs cannot be cleared.

(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 > Occupant Detection > Trouble Codes

HINT:

DTCs other than DTC B1790 may be output at this time, but they are not related to this check.

DTC B1790 is not output

USE SIMULATION METHOD TO CHECK

DTC B1790 is output

6.

REPLACE OCCUPANT DETECTION ECU

(a) Turn the power switch off.

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

(c) Replace the occupant detection ECU.

Click here

HINT:

Perform the inspection using parts from a normal vehicle when possible.

NEXT

7.

PERFORM ZERO POINT CALIBRATION

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

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

(c) Perform the zero point calibration.

Click here

"Zero Point Calibration is complete." is displayed

8.

PERFORM SENSITIVITY CHECK

(a) Perform the sensitivity check.

Click here

Standard:

27 to 33 kg (59.5 to 72.8 lb)

NEXT

9.

CHECK DTC

(a) Clear the DTCs.

Click here

Body Electrical > Occupant Detection > Clear DTCs

HINT:

  • First clear the DTCs stored in the occupant detection ECU, and then clear the DTCs stored in the airbag ECU assembly.
  • Use the Techstream to clear the DTCs of the occupant detection ECU, otherwise the DTCs cannot be cleared.

(b) Turn the power switch off.

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

(d) Check for DTCs.

Click here

Body Electrical > Occupant Detection > Trouble Codes

HINT:

DTCs other than DTC B1790 may be output at this time, but they are not related to this check.

DTC B1790 is not output

END (OCCUPANT DETECTION ECU WAS DEFECTIVE)
DTC B1790 is output

REPLACE AIRBAG ECU ASSEMBLY

10.

CHECK FRONT SEAT WIRE RH

(a) Disconnect the front seat wire RH connector from the floor wire.

*1

Front Seat Wire RH

*2

Floor Wire

*3

Occupant Detection ECU

*4

Airbag ECU Assembly

*5

Service Wire

*6

Connector E

*7

Connector D

*a

Front view of wire harness connector

(to Occupant Detection ECU)

*b

Front view of wire harness connector

(to Floor Wire)

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

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

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

Standard Voltage:

Tester Connection

Switch Condition

Specified Condition

Pf2-7 (FSR+) - Body ground

Power switch on (IG)

Below 1 V

Pf2-3 (FSR-) - Body ground

(e) Turn the power switch off.

(f) Disconnect the connector from the occupant detection ECU.

(g) Using a service wire, connect terminals 7 (FSR+) and 4 (FSR-) of connector E.

NOTICE:

Do not forcibly insert the service wire into the terminals of the connector.

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

Standard Resistance:

Tester Connection

Condition

Specified Condition

Pf2-7 (FSR+) - Pf2-3 (FSR-)

Always

Below 1 Ω

(i) Disconnect the service wire from connector E.

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

Standard Resistance:

Tester Connection

Condition

Specified Condition

Pf2-7 (FSR+) - Pf2-3 (FSR-)

Always

1 MΩ or higher

Pf2-7 (FSR+) - Body ground

Pf2-3 (FSR-) - Body ground
OK

REPLACE FLOOR WIRE
NG

REPLACE FRONT SEAT WIRE RH

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