Lexus RX (RX 350L, RX450h) 2016-2026 Repair Manual: Passenger Side Buckle Switch Circuit Malfunction (B1771)

DESCRIPTION

The passenger side buckle switch circuit consists of the occupant detection ECU and passenger side buckle switch (front seat inner belt assembly RH).

DTC B1771 is stored when a malfunction is detected in the passenger side buckle switch circuit.

DTC No.	Detection Item	DTC Detection Condition	Trouble Area
B1771	Passenger Side Buckle Switch Circuit Malfunction	The occupant detection ECU detects a line short, short to ground or B+, or an open in the passenger side buckle switch circuit. Passenger side buckle switch malfunction Occupant detection ECU malfunction	Passenger side buckle switch (Front seat inner belt assembly RH) Occupant detection ECU

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.

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PROCEDURE

1.	CHECK CONNECTORS

(a) Turn the engine switch off.

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

(c) Check that the connector is properly connected to the occupant detection ECU.

OK:

The connector is properly connected.

HINT:

If the connector is not properly connected, reconnect the connector and proceed to the next inspection.

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

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

OK:

The terminals are not deformed or damaged.

NG

REPLACE FRONT SEAT INNER BELT ASSEMBLY RH

OK

2.

CHECK DTC

(a) Connect the connector to the occupant detection ECU.

(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.

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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.

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Body Electrical > Occupant Detection > Trouble Codes

OK:

DTC B1771 is not output.

HINT:

Codes other than DTC B1771 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

3.	CHECK FRONT SEAT INNER BELT ASSEMBLY RH

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

(b) Replace the front seat inner belt assembly RH with a known good one.

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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 B1771 is not output.

HINT:

Codes other than DTC B1771 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 front seat inner belt assembly RH that was installed for testing to its original location.

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OK

REPLACE FRONT SEAT INNER BELT ASSEMBLY RH

NG

4.	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.

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

NEXT

5.	PERFORM ZERO POINT CALIBRATION

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

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Body Electrical > Occupant Detection > Utility

Tester Display
Zero Point Calibration

NEXT

END