Toyota Avalon (XX50) 2019-2022 Service & Repair Manual: 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.

• *: The front occupant classification sensor LH is built into the separate type front seat cushion spring assembly RH.

WIRING DIAGRAM

CAUTION / NOTICE / HINT

NOTICE:

After turning the power switch off, waiting time may be required before disconnecting the cable from the negative (-) auxiliary battery terminal. Therefore, make sure to read the disconnecting the cable from the negative (-) auxiliary 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

(a) Turn the power switch off.

(b) Disconnect the cable from the negative (-) auxiliary 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

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

*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) Turn the power switch on (IG).

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

Standard Voltage:

(d) Turn the power switch off.

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

(f) Using service wires, connect terminals 1 (SVC1) and 3 (SGD1), and terminals 2 (SIG1) and 3 (SGD1) of connector C.

NOTICE:

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

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

Standard Resistance:

(h) Disconnect the service wires from connector C.

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

Standard Resistance:

NG

REPLACE FRONT SEAT WIRE RH

OK

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

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

(c) Turn the power switch on (IG), and wait for at least 60 seconds.

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

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

(f) Turn the power switch off.

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

(h) Check for DTCs.

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 power switch off.

OK

USE SIMULATION METHOD TO CHECK

NG

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

(d) Turn the power switch on (IG), and wait for at least 60 seconds.

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

(f) Clear the DTCs stored in the airbag ECU assembly.

(g) Turn the power switch off.

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

(i) Check for DTCs.

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.

(j) Turn the power switch off.

(k) Disconnect the cable from the negative (-) auxiliary battery terminal.

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

Click here

NG

GO TO STEP 7

OK

(a) Turn the power switch off.

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

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

Click here

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

NEXT

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

Click here

NEXT

END

(a) Turn the power switch off.

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

(c) Replace the separate type front seat cushion spring assembly RH.

Click here

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

NEXT

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

Click here

NEXT

END