Lexus RX (RX 350L, RX450h) 2016-2026 Repair Manual: Front Occupant Classification Sensor LH Circuit Malfunction (B1780)

Lexus RX (RX 350L, RX450h) 2016-2026 Repair Manual / Vehicle Interior / Supplemental Restraint Systems / Occupant Classification System / Front Occupant Classification Sensor LH Circuit Malfunction (B1780)

DESCRIPTION

The front occupant classification sensor LH circuit consists of the occupant detection ECU and front occupant classification sensor LH.

DTC B1780 is stored when a malfunction is detected in the front occupant classification sensor LH circuit.

DTC No.

Detection Item

DTC Detection Condition

Trouble Area

B1780

Front Occupant Classification Sensor LH Circuit Malfunction
  • The occupant detection ECU detects a line short, short to ground or B+, or an open in the front occupant classification sensor LH circuit.
  • Front occupant classification sensor LH malfunction
  • Occupant detection ECU malfunction
  • Front seat wire RH
  • Front occupant classification sensor LH (Front seat adjuster assembly RH)*
  • Occupant detection ECU
  • *: The front occupant classification sensor LH is built into the front seat adjuster assembly RH.

WIRING DIAGRAM

CAUTION / NOTICE / HINT

NOTICE:

After turning the engine 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

HINT:

  • When DTC B1650 is stored as a result of troubleshooting for the airbag system, check the DTCs stored in the occupant detection ECU. When DTC B1780 is output, perform troubleshooting for this DTC first.
  • If it is difficult to perform troubleshooting (wire harness inspection), remove the front passenger seat installation bolts to see under the seat cushion.
  • In the above case, lift and hold the seat so that it does not fall down. Hold the seat only as necessary because holding the seat for a long period of time may cause seat rail deformation.

PROCEDURE

1.

CHECK CONNECTORS

(a) Turn the engine switch off.

(b) Disconnect the cable from the negative (-) battery terminal.

(c) Check that the connectors are properly connected to the occupant detection ECU and front occupant classification sensor LH.

OK:

The connectors are properly connected.

HINT:

If the connectors are not properly connected, reconnect the connectors and proceed to the next inspection.

(d) Disconnect the connectors from the occupant detection ECU and front occupant classification sensor LH.

(e) Check that the terminals of the connectors are not deformed or damaged.

OK:

The terminals are not deformed or damaged.

NG

REPLACE FRONT SEAT WIRE RH
OK

2.

CHECK FRONT SEAT WIRE RH (SHORT TO B+)

(a) Connect the cable to the negative (-) battery terminal.

*1

Front Occupant Classification Sensor LH

*2

Occupant Detection ECU

*3

Front Seat Wire RH

*a

Front view of wire harness connector

(to Occupant Detection ECU)

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

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

Standard Voltage:

Tester Connection

Condition

Specified Condition

b10-1 (SVC1) - Body ground

Engine switch on (IG)

Below 1 V

b10-3 (SIG1) - Body ground

Engine switch on (IG)

Below 1 V

b10-5 (SGD1) - Body ground

Engine switch on (IG)

Below 1 V

(d) Turn the engine switch off.

(e) Disconnect the cable from the negative (-) battery terminal.

NG

GO TO STEP 12

OK

3.

CHECK FRONT SEAT WIRE RH (OPEN)

(a) Using service wires, connect terminals 1 (SVC) and 3 (SGD), and terminals 2 (SIG) and 3 (SGD) of connector C.

NOTICE:

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

*1

Front Occupant Classification Sensor LH

*2

Occupant Detection ECU

*3

Front Seat Wire RH

*4

Service Wire

*a

Front view of wire harness connector

(to Occupant Detection ECU)

*b

Front view of wire harness connector

(to Front Occupant Classification Sensor LH)

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

Standard Resistance:

Tester Connection

Condition

Specified Condition

b10-1 (SVC1) - b10-5 (SGD1)

Always

Below 1 Ω

b10-3 (SIG1) - b10-5 (SGD1)

Always

Below 1 Ω

(c) Disconnect the service wires from connector C.

NG

REPLACE FRONT SEAT WIRE RH
OK

4.

CHECK FRONT SEAT WIRE RH (SHORT)

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

Standard Resistance:

Tester Connection

Condition

Specified Condition

b10-1 (SVC1) - b10-5 (SGD1)

Always

1 MΩ or higher

b10-3 (SIG1) - b10-5 (SGD1)

Always

1 MΩ or higher

b10-1 (SVC1) - b10-3 (SIG1)

Always

1 MΩ or higher

*1

Front Occupant Classification Sensor LH

*2

Occupant Detection ECU

*3

Front Seat Wire RH

*a

Front view of wire harness connector

(to Occupant Detection ECU)
NG

REPLACE FRONT SEAT WIRE RH
OK

5.

CHECK FRONT SEAT WIRE RH (SHORT TO GROUND)

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

Standard Resistance:

Tester Connection

Condition

Specified Condition

b10-1 (SVC1) - Body ground

Always

1 MΩ or higher

b10-3 (SIG1) - Body ground

Always

1 MΩ or higher

b10-5 (SGD1) - Body ground

Always

1 MΩ or higher

*1

Front Occupant Classification Sensor LH

*2

Occupant Detection ECU

*3

Front Seat Wire RH

*a

Front view of wire harness connector

(to Occupant Detection ECU)
NG

REPLACE FRONT SEAT WIRE RH
OK

6.

CHECK DTC

(a) Connect the connectors to the occupant detection ECU and front occupant classification sensor LH.

(b) Connect the cable to the negative (-) battery terminal.

(c) Clear the DTCs stored in the occupant detection ECU.

Click here

Body Electrical > Occupant Detection > Clear DTCs

(d) Clear the DTCs stored in the airbag sensor assembly.

Click here

Body Electrical > SRS Airbag > Clear DTCs

(e) Turn the engine switch off.

(f) Turn the engine switch on (IG), and wait for at least 10 seconds.

(g) Check for DTCs.

Click here

Body Electrical > Occupant Detection > Trouble Codes

OK:

DTC B1780 is not output.

HINT:

Codes other than DTC B1780 may be output at this time, but they are not related to this check.

(h) Turn the engine switch off.

OK

USE SIMULATION METHOD TO CHECK

NG

7.

CHECK OCCUPANT DETECTION ECU

(a) Disconnect the cable from the negative (-) battery terminal.

(b) Replace the occupant detection ECU with a known good one.

Click here

HINT:

Perform the following inspection using known good parts from another vehicle if possible.

(c) Connect the cable to the negative (-) battery terminal.

(d) Clear the DTCs stored in the occupant detection ECU.

Click here

Body Electrical > Occupant Detection > Clear DTCs

(e) Clear the DTCs stored in the airbag sensor assembly.

Click here

Body Electrical > SRS Airbag > Clear DTCs

(f) Turn the engine switch off.

(g) Turn the engine switch on (IG), and wait for at least 10 seconds.

(h) Check for DTCs.

Click here

Body Electrical > Occupant Detection > Trouble Codes

OK:

DTC B1780 is not output.

HINT:

Codes other than DTC B1780 may be output at this time, but they are not related to this check.

(i) Turn the engine switch off.

(j) Disconnect the cable from the negative (-) battery terminal.

(k) Restore the occupant detection ECU that was installed for testing to its original location.

Click here

NG

GO TO STEP 10

OK

8.

REPLACE OCCUPANT DETECTION ECU

(a) Turn the engine switch off.

(b) Disconnect the cable from the negative (-) battery terminal.

(c) Replace the occupant detection ECU with a new one.

Click here

(d) Connect the cable to the negative (-) battery terminal.

NEXT

9.

PERFORM ZERO POINT CALIBRATION

(a) Using the Techstream, perform Zero Point Calibration.

Click here

Body Electrical > Occupant Detection > Utility

Tester Display

Zero Point Calibration
NEXT

END

10.

REPLACE FRONT SEAT ADJUSTER ASSEMBLY RH

(a) Turn the engine switch off.

(b) Disconnect the cable from the negative (-) battery terminal.

(c) Replace the front seat adjuster assembly RH.

Click here

(d) Connect the cable to the negative (-) battery terminal.

NEXT

11.

PERFORM ZERO POINT CALIBRATION

(a) Using the Techstream, perform Zero Point Calibration.

Click here

Body Electrical > Occupant Detection > Utility

Tester Display

Zero Point Calibration
NEXT

END

12.

REPLACE FRONT SEAT ADJUSTER ASSEMBLY RH

(a) Replace the front seat adjuster assembly RH.

Click here

NOTICE:

Replace the front seat wire RH at the same time.

HINT:

When the front seat wire RH has a short to B+, the front occupant classification sensor LH will be damaged. Therefore, replace the front seat wire RH and the front seat adjuster assembly RH, which includes the front occupant classification sensor LH.

(b) Connect the cable to the negative (-) battery terminal.

NEXT

13.

PERFORM ZERO POINT CALIBRATION

(a) Using the Techstream, perform Zero Point Calibration.

Click here

Body Electrical > Occupant Detection > Utility

Tester Display

Zero Point Calibration
NEXT

END
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