Toyota Tundra Service Manual: Open in Occupant Classification ECU Battery Positive Line (B1794)

Toyota Tundra Service Manual / Vehicle Interior / Supplemental Restraint Systems / Occupant Classification System / Open in Occupant Classification ECU Battery Positive Line (B1794)

DESCRIPTION

DTC B1794 is set when a malfunction is detected in the occupant classification ECU.

DTC Code

DTC Detection Condition

Trouble Area

B1794

One of following conditions is met:

  • Occupant classification ECU circuit malfunction
  • Occupant classification ECU malfunction
  • Occupant classification ECU receives short circuit to ground signal in passenger side buckle switch circuit for 2 seconds
  • Harness or connector
  • Occupant classification ECU

HINT:

  • When DTC B1650/32 is detected as a result of troubleshooting the airbag system, perform troubleshooting for DTC B1794 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 ).
  • Inspect the fuses and relays for circuits related to this system before performing the following inspection procedure.

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 (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, and wait for at least 10 seconds.

(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 B1794 is not output.

HINT:

DTCs other than DTC B1794 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 center airbag sensor, occupant detection sensors and occupant classification ECU.

OK:

Connectors are properly connected.

NG

CONNECT CONNECTORS

OK

3.

CHECK CONNECTORS

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

OK:

Connectors are not deformed or damaged.

NG

REPLACE HARNESS OR CONNECTOR

OK

4.

CHECK HARNESS AND CONNECTOR (SOURCE VOLTAGE)

(a) Turn the ignition switch off.

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

(c) Disconnect the Y2 ECU connector.

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

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

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

Standard resistance:

Tester Connection

Condition

Specified Condition

Y2-3 (GND) - Body ground

Always

Below 1 Ω

Standard voltage:

Tester Connection

Switch Condition

Specified Condition

Y2-1 (+B) - Body ground

Always

11 to 14 V

Y2-7 (IG) - Body ground

Ignition switch ON

NG

REPLACE HARNESS OR CONNECTOR

OK

5.

CHECK FOR DTC

(a) Turn the ignition switch off.

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

(c) Connect the connectors to the occupant classification ECU.

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

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

(f) 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.

(g) Turn the ignition switch off, and wait for at least 10 seconds.

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

(i) Using the Techstream, check for DTCs of the occupant classification ECU (see page ).

OK:

DTC B1794 is not output.

HINT:

DTCs other than DTC B1794 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 (see page ).
  • for Power Seat (see page ).

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 (see page ).

NEXT

8.

PERFORM SENSITIVITY CHECK

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

Standard range:

27 to 33 kg (59.5 to 72.8 lb)

NEXT

END

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