Lexus NX: Front Fog Light Circuit

DESCRIPTION

Illumination of the front fog lights is controlled by the main body ECU (multiplex network body ECU).

WIRING DIAGRAM

CAUTION / NOTICE / HINT

NOTICE:

  • Inspect the fuses for circuits related to this system before performing the following inspection procedure.
  • Before performing troubleshooting, check that the taillight circuit operates properly.
  • 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 (FRONT FOG LIGHT 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

Front Fog Light Relay

Front fog light relay

ON or OFF

The headlight dimmer switch is in the tail position

Body Electrical > Main Body > Active Test

Tester Display

Front Fog Light Relay

Result

Proceed to

The Active Test is performed normally

A

The Active Test is not performed normally for both fog lights

B

The Active Test is not performed normally for the right side fog light only

C

The Active Test is not performed normally for the left side fog light only

D

A

PROCEED TO NEXT SUSPECTED AREA SHOWN IN PROBLEM SYMPTOMS TABLE

C

GO TO STEP 9

D

GO TO STEP 10

B

2.

CHECK FRONT FOG LIGHT RELAY (FOG FR)

(a) Remove the front fog light relay from the No. 2 engine room relay block.

(b) Inspect the fog light relay.

Click here

NG

REPLACE FOG LIGHT RELAY (FOG FR)

OK

3.

CHECK HARNESS AND CONNECTOR (FRONT FOG LIGHT RELAY [FOG FR] - BATTERY)

(a) Remove the front fog light relay from the No. 2 engine room relay block.

*a

Front view of wire harness connector

(to Front Fog Light Relay [FOG FR])

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

Standard Voltage:

Tester Connection

Switch Condition

Specified Condition

Relay terminal 3 - Body ground

Power switch off

11 to 14 V

NG

REPAIR OR REPLACE HARNESS OR CONNECTOR

OK

4.

CHECK HARNESS AND CONNECTOR (TAILLIGHT RELAY [TAIL RELAY] - FRONT FOG LIGHT RELAY [FOG FR])

(a) Remove the front fog light relay from the No. 2 engine room relay block.

*a

Front view of wire harness connector

(to Front Fog Light Relay [FOG FR])

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

Standard Voltage:

Tester Connection

Switch Condition

Specified Condition

If the low beams are illuminated, shine a light on the automatic light control sensor to change the system to daytime mode.

Relay terminal 1 - Body ground

Headlight dimmer switch in AUTO with low beams off → low beams on

Below 1 V → 11 to 14 V

NG

GO TO STEP 7

OK

5.

CHECK HARNESS AND CONNECTOR (FRONT FOG LIGHT RELAY [FOG FR] - FOG LIGHT ASSEMBLY AND BODY GROUND)

(a) Remove the front fog light relay from the No. 2 engine room relay block.

(b) Disconnect the A67 fog light assembly LH connector.

(c) Disconnect the A74 fog light assembly RH connector.

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

Standard Resistance:

Tester Connection

Condition

Specified Condition

Relay terminal 5 - A67-2 (B)

Always

Below 1 Ω

Relay terminal 5 - A74-2 (B)

Always

Below 1 Ω

A67-1 (E) - Body ground

Always

Below 1 Ω

A74-1 (E) - Body ground

Always

Below 1 Ω

Relay terminal 5 or A67-2 (B) - Body ground

Always

10 kΩ or higher

Relay terminal 5 or A74-2 (B) - Body ground

Always

10 kΩ or higher

NG

REPAIR OR REPLACE HARNESS OR CONNECTOR

OK

6.

CHECK HARNESS AND CONNECTOR (FRONT FOG LIGHT RELAY [FOG FR] - MAIN BODY ECU [MULTIPLEX NETWORK BODY ECU])

(a) Remove the front fog light relay from the No. 2 engine room relay block.

(b) Remove the instrument panel junction block assembly.

Click here

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

Click here

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

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

Standard Resistance:

Tester Connection

Condition

Specified Condition

Relay terminal 2 - A-7 (FFGO)

Always

Below 1 Ω

Relay terminal 2 or A-7 (FFGO) - Body ground

Always

10 kΩ or higher

OK

REPLACE MAIN BODY ECU (MULTIPLEX NETWORK BODY ECU)

NG

GO TO STEP 8

7.

CHECK HARNESS AND CONNECTOR (FRONT FOG LIGHT RELAY [FOG FR] - INSTRUMENT PANEL JUNCTION BLOCK ASSEMBLY)

(a) Remove the front fog light relay 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-25

Always

Below 1 Ω

Relay terminal 1 or 4B-25 - Body ground

Always

10 kΩ or higher

OK

REPLACE INSTRUMENT PANEL JUNCTION BLOCK ASSEMBLY

NG

REPAIR OR REPLACE HARNESS OR CONNECTOR

8.

CHECK HARNESS AND CONNECTOR (FRONT FOG LIGHT RELAY [FOG FR] - INSTRUMENT PANEL JUNCTION BLOCK ASSEMBLY)

(a) Remove the front fog light relay 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 2 - 4B-56

Always

Below 1 Ω

Relay terminal 2 or 4B-56 - Body ground

Always

10 kΩ or higher

OK

REPLACE INSTRUMENT PANEL JUNCTION BLOCK ASSEMBLY

NG

REPAIR OR REPLACE HARNESS OR CONNECTOR

9.

CHECK HARNESS AND CONNECTOR (FRONT FOG LIGHT RELAY [FOG FR] - FOG LIGHT ASSEMBLY RH)

(a) Remove the front fog light relay from the No. 2 engine room relay block.

(b) Disconnect the A74 fog light assembly RH connector.

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

Standard Resistance:

Tester Connection

Condition

Specified Condition

Relay terminal 5 - A74-2 (B)

Always

Below 1 Ω

A74-1 (E) - Body ground

Always

Below 1 Ω

Relay terminal 5 or A74-2 (B) - Body ground

Always

10 kΩ or higher

OK

REPLACE FOG LIGHT ASSEMBLY RH

NG

REPAIR OR REPLACE HARNESS OR CONNECTOR

10.

CHECK HARNESS AND CONNECTOR (FRONT FOG LIGHT RELAY [FOG FR] - FOG LIGHT ASSEMBLY LH)

(a) Remove the front fog light relay from the No. 2 engine room relay block.

(b) Disconnect the A67 fog light assembly LH connector.

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

Standard Resistance:

Tester Connection

Condition

Specified Condition

Relay terminal 5 - A67-2 (B)

Always

Below 1 Ω

A67-1 (E) - Body ground

Always

Below 1 Ω

Relay terminal 5 or A67-2 (B) - Body ground

Always

10 kΩ or higher

OK

REPLACE FOG LIGHT ASSEMBLY LH

NG

REPAIR OR REPLACE HARNESS OR CONNECTOR

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