Toyota Tundra Service Manual: Occupant Classification Sensor Power Supply Circuit Malfunction (B1793)

DESCRIPTION

The occupant detection sensor power supply circuit consists of the occupant classification ECU and the occupant detection sensors.

DTC B1793 is set when a malfunction is detected in the occupant detection sensor power supply circuit.

HINT:

• When DTC B1650/32 is detected as a result of troubleshooting the airbag system, perform troubleshooting for DTC B1793 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 (See page ).
• When disconnecting the cable from the negative (-) battery terminal while performing repairs, some systems need to be initialized after the cable is reconnected (See page ).

HINT:

• If troubleshooting (wire harness inspection) is difficult to perform, remove the front seat RH 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

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

(b) Clear any DTCs stored in the memory (see page ).

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 (see page ).

OK:

DTC B1793 is not output.

HINT:

DTCs other than DTC B1793 may be output at this time, but they are not related to this check.

OK

USE SIMULATION METHOD TO CHECK

NG

(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 occupant detection sensors.

OK:

Connectors are properly connected.

NG

CONNECT CONNECTORS

OK

(a) Check that the connectors (on the occupant classification ECU side and the occupant detection sensors side) are not damaged (see page ).

OK:

Connectors are not deformed or damaged.

NG

REPLACE FRONT SEAT WIRE RH

OK

(a) Disconnect the connectors from the occupant classification ECU and the 4 occupant detection sensors.

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

Standard voltage:

(e) Turn the ignition switch off.

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

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

Standard resistance:

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

Standard resistance:

NG

REPLACE FRONT SEAT WIRE RH

OK

(a) Connect the connectors to the occupant classification ECU and the 4 occupant detection sensors.

(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 (see page ).

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.

(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 (see page ).

OK:

DTC B1793 is not output.

HINT:

DTCs other than DTC B1793 may be output at this time, but they are not related to this check.

OK

USE SIMULATION METHOD TO CHECK

NG

(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 (see page )
• for Power Seat (see page )

HINT:

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

NEXT

(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 (see page ).

NEXT

(a) Using the Techstream, perform the sensitivity check (see page ).

Standard range:

27 to 33 kg (59.5 to 72.8 lb)

NEXT

END