Lexus NX: Low Beam Headlight Circuit

DESCRIPTION

The main body ECU (multiplex network body ECU) controls the low beam headlights.

WIRING DIAGRAM

CAUTION / NOTICE / HINT

NOTICE:

  • Inspect the fuses for circuits related to this system before performing the following procedure.
  • Recognition code registration is necessary when replacing the main body ECU (multiplex network body ECU).
  • If the main body ECU (multiplex network body ECU) is replaced, refer to Registration.

PROCEDURE

1.

PERFORM ACTIVE TEST USING TECHSTREAM (HEADLIGHT RELAY)

(a) Using the Techstream, perform the Active Test.

Click here

Body Electrical > Main Body > Active Test

Tester Display

Measurement Item

Control Range

Diagnostic Note

Headlight Relay

Low beam headlight relay

ON or OFF

-

Body Electrical > Main Body > Active Test

Tester Display

Headlight Relay

OK:

Headlight relay operates. (Low beam headlights illuminate with the appropriate brightness.)

OK

PROCEED TO NEXT SUSPECTED AREA SHOWN IN PROBLEM SYMPTOMS TABLE

NG

2.

INSPECT HEADLIGHT RELAY (H-LP [LO])

(a) Remove the headlight relay (H-LP [LO]) from the No. 2 engine room relay block.

(b) Inspect the headlight light relay (H-LP [LO]).

NG

REPLACE HEADLIGHT RELAY (H-LP [LO])

OK

3.

CHECK HARNESS AND CONNECTOR (HEADLIGHT RELAY [H-LP (LO)] - BATTERY)

(a) Remove the headlight relay (H-LP [LO]) from the No. 2 engine room relay block.

*a

Front view of wire harness connector

(to Headlight Relay [H-LP (LO)])

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

Standard Voltage:

Tester Connection

Switch Condition

Specified Condition

Relay terminal 5 - Body ground

Power switch off

11 to 14 V

Relay terminal 2 - Body ground

Power switch off

11 to 14 V

NG

REPAIR OR REPLACE HARNESS OR CONNECTOR

OK

4.

CHECK HARNESS AND CONNECTOR (HEADLIGHT RELAY [H-LP (LO)] - HEADLIGHT ASSEMBLY)

  • *1: for LH
  • *2: for RH

(a) Remove the headlight relay (H-LP [LO]) from the No. 2 engine room relay block.

(b) Disconnect the A66*1 and A68*2 headlight assembly connector.

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

Standard Resistance:

for LH

Tester Connection

Condition

Specified Condition

Relay terminal 3 - A66-3 (LO)

Always

Below 1 Ω

Headlight relay terminal 3 - Body ground

Always

10 kΩ or higher

for RH

Tester Connection

Condition

Specified Condition

Relay terminal 3 - A68-3 (LO)

Always

Below 1 Ω

Headlight relay terminal 3 - Body ground

Always

10 kΩ or higher

NG

REPAIR OR REPLACE HARNESS OR CONNECTOR

OK

5.

CHECK HARNESS AND CONNECTOR (HEADLIGHT RELAY [H-LP (LO)] - INSTRUMENT PANEL JUNCTION BLOCK ASSEMBLY)

(a) Remove the headlight relay (H-LP [LO]) from the No. 2 engine room relay block.

(b) Disconnect the 4B instrument panel junction block assembly connector.

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

Standard Resistance:

Tester Connection

Condition

Specified Condition

Relay terminal 1 - 4B-53

Always

Below 1 Ω

Relay terminal 1 or 4B-53 - Body ground

Always

10 kΩ or higher

NG

REPAIR OR REPLACE HARNESS OR CONNECTOR

OK

6.

INSPECT INSTRUMENT PANEL JUNCTION BLOCK ASSEMBLY

(a) Remove the instrument panel junction block assembly.

Click here

(b) Remove the main body ECU (multiplex network body ECU) from the instrument panel junction block assembly.

Click here

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

Standard Resistance:

Tester Connection

Condition

Specified Condition

A-15 (HRLY) - 4B-53

Always

Below 1 Ω

OK

REPLACE MAIN BODY ECU (MULTIPLEX NETWORK BODY ECU)

NG

REPLACE INSTRUMENT PANEL JUNCTION BLOCK ASSEMBLY

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