Lexus RX (RX 350L, RX450h) 2016-2025 Repair Manual: Curtain Shield Airbag Sensor Initialization Error (LH) (B1638)

DESCRIPTION

The side collision sensor LH circuit (bus 1) consists of the airbag sensor assembly, door side airbag sensor LH and rear airbag sensor LH.

The door side airbag sensor LH and rear airbag sensor LH detect impacts to the vehicle and send signals to the airbag sensor assembly to determine if the airbags and pretensioners should be deployed.

DTC B1638 is stored when a malfunction is detected in the side collision sensor LH circuit (bus 1).

DTC No.	Detection Item	DTC Detection Condition	Trouble Area	Warning Indicate	Test Mode / Check Mode
B1638	Curtain Shield Airbag Sensor Initialization Error (LH)	The airbag sensor assembly detects a line short, short to ground or B+, or an open in the side collision sensor LH circuit (bus 1). Rear airbag sensor LH malfunction Airbag sensor assembly malfunction	No. 2 floor wire Front door wire LH Rear airbag sensor LH Airbag sensor assembly	Comes on	Does not apply to test/check mode

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

PROCEDURE

1.	CHECK HISTORY DTC

(a) Check for history DTCs.

Body Electrical > SRS Airbag > Trouble Codes

HINT:

Codes other than history DTC B1637 may be output at this time, but they are not related to this check.

Result	Proceed to
History DTC B1637 is not output.	A
History DTC B1637 is output.	B

B

GO TO DTC B1637

A

2.	CHECK CONNECTION OF CONNECTORS

(a) Turn the engine switch off.

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

CAUTION:

Wait at least 90 seconds after disconnecting the cable from the negative (-) battery terminal to disable the SRS system.

(c) Check that the connectors are properly connected to the airbag sensor assembly, door side airbag sensor LH and rear airbag sensor LH. Also check that the connectors that link the No. 2 floor wire and front door wire LH are properly connected.

OK:

The connectors are properly connected.

NG

CONNECT CONNECTORS PROPERLY

OK

3.	CHECK CONNECTORS

(a) Disconnect the connectors from the airbag sensor assembly, door side airbag sensor LH and rear airbag sensor LH. Also disconnect the connectors that link the No. 2 floor wire and front door wire LH.

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

OK:

The terminals are not deformed or damaged.

NG

REPLACE NO. 2 FLOOR WIRE OR FRONT DOOR WIRE LH

OK

4.	CHECK NO. 2 FLOOR WIRE

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

*1 Rear Airbag Sensor LH *2 Airbag Sensor Assembly *3 No. 2 Floor Wire *4 Service Wire *a Front view of wire harness connector (to Airbag Sensor Assembly) *b Front view of wire harness connector (to Rear Airbag Sensor LH)

(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
S15-4 (BCL+) - Body ground	Engine switch on (IG)	Below 1 V
S15-3 (BCL-) - Body ground	Engine switch on (IG)	Below 1 V

(d) Turn the engine switch off.

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

CAUTION:

Wait at least 90 seconds after disconnecting the cable from the negative (-) battery terminal to disable the SRS system.

(f) Using a service wire, connect terminals 32 (BBL+) and 31 (BBL-) of connector B.

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:

Tester Connection	Condition	Specified Condition
S15-4 (BCL+) - S15-3 (BCL-)	Always	Below 1 Ω

(h) Disconnect the service wire from connector B.

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

Standard Resistance:

Tester Connection	Condition	Specified Condition
S15-4 (BCL+) - S15-3 (BCL-)	Always	1 MΩ or higher
S15-4 (BCL+) - Body ground	Always	1 MΩ or higher
S15-3 (BCL-) - Body ground	Always	1 MΩ or higher

NG

REPLACE NO. 2 FLOOR WIRE

OK

5.	CHECK WIRE HARNESS

(a) Connect the connectors that link the No. 2 floor wire and front door wire LH.

*1 Door Side Airbag Sensor LH *2 Rear Airbag Sensor LH *3 Front Door Wire LH *4 No. 2 Floor Wire *5 Service Wire *a Front view of wire harness connector (to Rear Airbag Sensor LH) *b Front view of wire harness connector (to Door Side Airbag Sensor LH)

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

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

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

Standard Voltage:

Tester Connection	Condition	Specified Condition
S15-1 (BDL+) - Body ground	Engine switch on (IG)	Below 1 V
S15-2 (BDL-) - Body ground	Engine switch on (IG)	Below 1 V

(e) Turn the engine switch off.

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

CAUTION:

Wait at least 90 seconds after disconnecting the cable from the negative (-) battery terminal to disable the SRS system.

(g) Using a service wire, connect terminals 2 (BDL+) and 1 (BDL-) of connector E.

NOTICE:

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

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

Standard Resistance:

Tester Connection	Condition	Specified Condition
S15-1 (BDL+) - S15-2 (BDL-)	Always	Below 1 Ω

(i) Disconnect the service wire from connector E.

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

Standard Resistance:

Tester Connection	Condition	Specified Condition
S15-1 (BDL+) - S15-2 (BDL-)	Always	1 MΩ or higher
S15-1 (BDL+) - Body ground	Always	1 MΩ or higher
S15-2 (BDL-) - Body ground	Always	1 MΩ or higher

NG

GO TO STEP 7

OK

6.	CHECK REAR AIRBAG SENSOR LH

(a) Connect the connectors to the door side airbag sensor LH and airbag sensor assembly.

*1 Rear Airbag Sensor RH *2 Airbag Sensor Assembly

(b) Interchange the rear airbag sensor LH with RH and connect the connectors.

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

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

(e) Clear the DTCs stored in memory.

Body Electrical > SRS Airbag > Clear DTCs

(f) Turn the engine switch off.

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

(h) Check for DTCs.

Body Electrical > SRS Airbag > Trouble Codes

HINT:

Codes other than DTCs B1633 and B1638 may be output at this time, but they are not related to this check.

Result	Proceed to
DTC B1638 is output.	A
DTC B1633 is output.	B
DTCs B1633 and B1638 are not output.	C

(i) Turn the engine switch off.

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

CAUTION:

Wait at least 90 seconds after disconnecting the cable from the negative (-) battery terminal to disable the SRS system.

(k) Return the rear airbag sensor LH and RH to their original positions and connect the connectors.

A

REPLACE AIRBAG SENSOR ASSEMBLY

B

REPLACE REAR AIRBAG SENSOR LH

C

USE SIMULATION METHOD TO CHECK

7.	CHECK NO. 2 FLOOR WIRE

(a) Disconnect the No. 2 floor wire connector from the front door wire LH.

*1 Door Side Airbag Sensor LH *2 Rear Airbag Sensor LH *3 Front Door Wire LH *4 No. 2 Floor Wire *5 Service Wire *a Front view of wire harness connector (to Rear Airbag Sensor LH) *b Front view of wire harness connector (to Front Door Wire LH)

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

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

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

Standard Voltage:

Tester Connection	Condition	Specified Condition
NS1-21 (BDL+) - Body ground	Engine switch on (IG)	Below 1 V
NS1-39 (BDL-) - Body ground	Engine switch on (IG)	Below 1 V

(e) Turn the engine switch off.

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

CAUTION:

Wait at least 90 seconds after disconnecting the cable from the negative (-) battery terminal to disable the SRS system.

(g) Using a service wire, connect terminals 1 (BDL+) and 2 (BDL-) of connector B.

NOTICE:

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

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

Standard Resistance:

Tester Connection	Condition	Specified Condition
NS1-21 (BDL+) - NS1-39 (BDL-)	Always	Below 1 Ω

(i) Disconnect the service wire from connector B.

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

Standard Resistance:

Tester Connection	Condition	Specified Condition
NS1-21 (BDL+) - NS1-39 (BDL-)	Always	1 MΩ or higher
NS1-21 (BDL+) - Body ground	Always	1 MΩ or higher
NS1-39 (BDL-) - Body ground	Always	1 MΩ or higher

OK

REPLACE FRONT DOOR WIRE LH

NG

REPLACE NO. 2 FLOOR WIRE