Toyota Tundra Service Manual: Center Airbag Sensor Assembly Communication Circuit Malfunction (B1790)

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

DESCRIPTION

The center airbag sensor communication circuit consists of the occupant classification ECU and the center airbag sensor.

DTC B1790 is set when a malfunction is detected in the center airbag sensor communication circuit.

DTC Code

DTC Detection Condition

Trouble Area

B1790

One of following conditions is met:

  • Occupant classification ECU receives line short circuit signal, open circuit signal, short circuit to ground signal or short circuit to +B signal in center airbag sensor communication circuit for 2 seconds
  • Center airbag sensor malfunction
  • Occupant classification ECU malfunction
  • No. 2 floor wire
  • Front seat wire RH
  • Occupant classification ECU
  • Center airbag sensor

HINT:

  • When DTC B1630 is detected 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 classification ECU, otherwise the DTCs cannot be read.

WIRING DIAGRAM

CAUTION / NOTICE / HINT

NOTICE:

  • After turning the ignition 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 ).
  • When disconnecting the cable from the negative (-) battery terminal while performing repairs, some systems need to be initialized after the cable is reconnected (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 FOR DTC

(a) Turn the ignition switch to ON, and wait for at least 60 seconds.

(b) Clear any DTCs stored in the memory (Click here ).

HINT:

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

(c) Turn the ignition switch off.

(d) Turn the ignition switch to ON, and wait for at least 60 seconds.

(e) Using the Techstream, check for DTCs of the occupant classification ECU (Click here ).

OK:

DTC B1790 is not output.

HINT:

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

OK

USE SIMULATION METHOD TO CHECK

NG

2.

CHECK CONNECTION OF CONNECTORS

(a) Turn the ignition switch off.

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

(c) Check that the connectors are properly connected to the occupant classification ECU and the center airbag sensor.

OK:

Connectors are properly connected.

NG

CONNECT CONNECTORS

OK

3.

CHECK CONNECTORS

(a) Check that the connectors (on the center airbag sensor side and occupant classification ECU side) are not damaged (Click here ).

OK:

Connectors are not deformed or damaged.

NG

REPLACE HARNESS OR CONNECTOR

OK

4.

CHECK OCCUPANT CLASSIFICATION SYSTEM CIRCUIT

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

*1

Occupant Classification ECU

*2

Center Airbag Sensor

*3

Front Seat Wire RH

*4

No. 2 Floor Wire

*5

Service Wire

*a

Front view of wire harness connector

(to Occupant Classification ECU)

*b

Front view of wire harness connector

(to Center Airbag Sensor)

(b) Turn the ignition switch to ON.

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

Standard Voltage:

Tester Connection

Switch Condition

Specified Condition

Y2-8 (FSR+) - Body ground

Ignition switch ON

Below 1 V

Y2-4 (FSR-) - Body ground

Ignition switch ON

Below 1 V

(d) Turn the ignition switch off.

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

(f) Using a service wire, connect terminals 32 (FSR+) and 31 (FSR-) of connector B.

NOTICE:

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

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

Standard Resistance:

Tester Connection

Condition

Specified Condition

Y2-8 (FSR+) - Y2-4 (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

Y2-8 (FSR+) - Y2-4 (FSR-)

Always

1 MΩ or higher

Y2-8 (FSR+) - Body ground

Always

1 MΩ or higher

Y2-4 (FSR-) - Body ground

Always

1 MΩ or higher

NG

GO TO STEP 10

OK

5.

CHECK FOR DTC

(a) Connect the connectors to the occupant classification ECU and the center airbag sensor.

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

(c) Turn the ignition switch to ON, and wait for at least 60 seconds.

(d) Clear any DTCs stored in the memory (Click here ).

HINT:

  • First clear any DTCs stored in the occupant classification ECU and then in the center airbag sensor.
  • Use the Techstream to clear the DTCs of the occupant classification ECU, otherwise the DTCs cannot be cleared.

(e) Turn the ignition switch off.

(f) Turn the ignition switch to ON, and wait for at least 60 seconds.

(g) Using the Techstream, check for DTCs of the occupant classification ECU (Click here ).

OK:

DTC B1790 is not output.

HINT:

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

OK

USE SIMULATION METHOD TO CHECK

NG

6.

REPLACE OCCUPANT CLASSIFICATION ECU

(a) Turn the ignition switch off.

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

(c) Replace the occupant classification ECU.

  • for Manual Seat (Click here ).
  • for Power Seat (Click here ).

HINT:

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

NEXT

7.

PERFORM ZERO POINT CALIBRATION

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

(b) Connect the Techstream to the DLC3.

(c) Turn the ignition switch to ON, and wait for at least 60 seconds.

(d) Using the Techstream, perform the zero point calibration (Click here ).

NEXT

8.

PERFORM SENSITIVITY CHECK

(a) Using the Techstream, perform the sensitivity check (Click here ).

Standard range:

27 to 33 kg (59.5 to 72.8 lb)

NEXT

9.

CHECK FOR DTC

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

(b) Turn the ignition switch to ON, and wait for at least 60 seconds.

(c) Clear any DTCs stored in the memory (Click here ).

HINT:

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

(d) Turn the ignition switch off.

(e) Turn the ignition switch to ON, and wait for at least 60 seconds.

(f) Using the Techstream, check for DTCs of the occupant classification ECU (Click here ).

OK:

DTC B1790 is not output.

HINT:

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

Result

Result

Proceed to

DTC B1790 is not output

A

DTC B1790 is output (for Column Shift Type)

B

DTC B1790 is output (for Floor Shift Type)

C

A

END

B

REPLACE CENTER AIRBAG SENSOR

C

REPLACE CENTER AIRBAG SENSOR

10.

CHECK NO.2 FLOOR WIRE

(a) Disconnect the instrument panel wire connector from the engine room main wire.

*1

Occupant Classification ECU

*2

Center Airbag Sensor

*3

Front Seat Wire RH

*4

No. 2 Floor Wire

*5

Service Wire

*a

Front view of wire harness connector

(to Front Seat Wire RH)

*b

Front view of wire harness connector

(to Center Airbag Sensor)

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

(c) Turn the ignition switch to ON.

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

Standard Voltage:

Tester Connection

Switch Condition

Specified Condition

QY1-1 (FSR+) - Body ground

Ignition switch ON

Below 1 V

QY1-4 (FSR-) - Body ground

Ignition switch ON

Below 1 V

(e) Turn the ignition switch off.

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

(g) Using a service wire, connect terminals 32 (FSR+) and 31 (FSR-) of connector B.

NOTICE:

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

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

Standard Resistance:

Tester Connection

Condition

Specified Condition

QY1-1 (FSR+) - QY1-4 (FSR-)

Always

Below 1 Ω

(i) Disconnect the service wire from connector B.

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

Standard Resistance:

Tester Connection

Condition

Specified Condition

QY1-1 (FSR+) - QY1-4 (FSR-)

Always

1 MΩ or higher

QY1-1 (FSR+) - Body ground

Always

1 MΩ or higher

QY1-4 (FSR-) - Body ground

Always

1 MΩ or higher

OK

REPLACE FRONT SEAT WIRE RH

NG

REPLACE NO. 2 FLOOR WIRE

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