Toyota Tundra Service Manual: Headlight Relay Circuit

DESCRIPTION

The main body ECU (multiplex network body ECU) receives light control switch information signals and illuminates the low beam headlights.

WIRING DIAGRAM

CAUTION / NOTICE / HINT

NOTICE:

Inspect the bulbs and fuses for circuits related to this system before performing the following procedure.

PROCEDURE

1.

PERFORM ACTIVE TEST USING TECHSTREAM

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

Click here

Main Body

Tester Display

Test Part

Control Range

Diagnostic Note

Headlight

Headlight relay (H-LP LO)

OFF or ON

-

OK:

Headlight relay (H-LP LO) operates (low beam headlights turn on).

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 engine room relay block and junction block.

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

Click here

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 engine room relay block and junction 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

Condition

Specified Condition

Headlight relay (H-LP LO) terminal 3 - Body ground

Always

11 to 14 V

Headlight relay terminal (H-LP LO) 1 - Body ground

Always

11 to 14 V

NG

REPAIR OR REPLACE HARNESS OR CONNECTOR

OK

4.

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

(a) Remove the headlight relay (H-LP LO) from the engine room relay block and junction block.

(b) Disconnect the 3H driver side junction block assembly connector.

(c) for Halogen Headlight:

(1) Disconnect the A8 headlight assembly LH connector.

(2) Disconnect the A9 headlight assembly RH connector.

(d) for LED Headlight:

(1) Disconnect the A59 headlight assembly LH connector.

(2) Disconnect the A58 headlight assembly RH connector.

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

Standard Resistance:

for Halogen Headlight

Tester Connection

Condition

Specified Condition

Headlight relay (H-LP LO) terminal 2 - 3H-31

Always

Below 1 Ω

Headlight relay (H-LP LO) terminal 5 - A8-1 (LO)

Always

Below 1 Ω

Headlight relay (H-LP LO) terminal 2 or 3H-31 - Body ground

Always

10 kΩ or higher

Headlight relay (H-LP LO) terminal 5 or A8-1 (LO) - Body ground

Always

10 kΩ or higher

for LED Headlight

Tester Connection

Condition

Specified Condition

Headlight relay (H-LP LO) terminal 2 - 3H-31

Always

Below 1 Ω

Headlight relay (H-LP LO) terminal 5 - A59-2 (LO)

Always

Below 1 Ω

Headlight relay (H-LP LO) terminal 2 or 3H-31 - Body ground

Always

10 kΩ or higher

Headlight relay (H-LP LO) terminal 5 or A59-2 (LO) - Body ground

Always

10 kΩ or higher

NG

REPAIR OR REPLACE HARNESS OR CONNECTOR

OK

5.

CHECK DRIVER SIDE JUNCTION BLOCK ASSEMBLY

(a) Remove the driver side junction block assembly.

Click here

*a

Component without harness connected

(Driver Side Junction Block Assembly)

(b) Remove the main body ECU (multiplex network body ECU) from the driver side 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) - 3H-31

Always

Below 1 Ω

OK

REPLACE MAIN BODY ECU (MULTIPLEX NETWORK BODY ECU)

NG

REPLACE DRIVER SIDE JUNCTION BLOCK ASSEMBLY

    Headlight Dimmer Switch Circuit

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