LIGHTING SYSTEM Headlight Relay Circuit

DESCRIPTION

The main body ECU receives the light control switch head signal to control the headlight relay. When the light control switch is in the AUTO position, the main body ECU receives the ambient light level signal from the automatic light control sensor to control the headlight relay.

Tech Tips


  • This circuit is only for vehicles with automatic light control or daytime running light control.

  • If the vehicle has automatic light control or daytime running light control, the exterior lights (headlights, taillights, front fog lights* and rear fog light) are controlled by the main body ECU.

  • If the vehicle does not have automatic light control or daytime running light control, the exterior lights (headlights, taillights, front fog lights* and rear fog light) are not controlled by the main body ECU. Perform troubleshooting according to the Problem Symptoms Table Click here.

  • If a low beam headlight on only one side does not illuminate, inspect any bulb, fuse or wire harness that is related to the headlight.

  • If both the right and left low beam headlights do not illuminate when the light control switch is turned to the head position, perform the headlight relay Active Test and read the light control switch head signal value in the Data List to determine if the malfunction exists on either the switch side or the relay side.


  • *: w/ Front Fog Light

WIRING DIAGRAM

A01INXIE01
A01IPGBE01

INSPECTION PROCEDURE

Note

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

PROCEDURE


  1. PERFORM ACTIVE TEST USING INTELLIGENT TESTER (HEADLIGHT RELAY)


    1. Using the intelligent tester, perform the Active Test Click here.

      Main Body
      Tester Display Test Part Control Range Diagnostic Note
      Headlight Relay Headlight Relay ON/OFF -
      OK
      Headlight relay operates (low beam headlights illuminate).

    NG

    READ VALUE USING INTELLIGENT TESTER (HEADLIGHT SWITCH) Click here

    OK

    PROCEED TO NEXT SUSPECTED AREA SHOWN IN PROBLEM SYMPTOMS TABLE Click here

  2. READ VALUE USING INTELLIGENT TESTER (HEADLIGHT SWITCH)


    1. Using the intelligent tester, read the Data List Click here.

      Main Body
      Tester Display Measurement Item/Range Normal Condition Diagnostic Note
      Head Light SW (Head) Light control switch head signal / ON or OFF

      ON: Light control switch in head

      OFF: Light control switch not in head

      		 -
      OK
      The display is as specified in the normal condition column.

    NG

    PROCEED TO NEXT SUSPECTED AREA SHOWN IN PROBLEM SYMPTOMS TABLE Click here

    OK

  3. CHECK HARNESS AND CONNECTOR (BATTERY - H-LP LH LO AND H-LP RH LO FUSE TERMINAL)


    1. A01IPZ7E03
      Text in Illustration
      *1 Engine Room No. 1 Relay Block, Junction Block
      *2 H-LP LH LO Fuse
      *3 H-LP RH LO Fuse

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

      Standard Voltage
      Tester Connection Switch Condition Specified Condition
      H-LP LH LO fuse terminal - Body ground Light control switch off Below 1 V
      Light control switch head 11 to 14 V
      H-LP RH LO fuse terminal - Body ground Light control switch off Below 1 V
      Light control switch head 11 to 14 V

    NG

    INSPECT HEADLIGHT RELAY (H-LP) Click here

    OK

    REPAIR OR REPLACE HARNESS OR CONNECTOR (HEADLIGHT RELAY [H-LP] - HEADLIGHT ASSEMBLY)

  4. INSPECT HEADLIGHT RELAY (H-LP)


    1. A01IOIQE02

      Remove the headlight relay from the engine room No. 1 relay block, junction block.

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

      Standard Resistance
      Tester Connection Condition Specified Condition
      3 - 5 Battery voltage not applied between terminals 1 and 2 10 kΩ or higher
      3 - 5 Battery voltage applied between terminals 1 and 2 Below 1 Ω

    NG

    REPLACE HEADLIGHT RELAY

    OK

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


    1. A01IQQ2E02
      Text in Illustration
      *1 Engine Room No. 1 Relay Block, Junction Block
      *2 Headlight Relay (H-LP)

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

      Standard Voltage
      Tester Connection Condition Specified Condition
      Headlight relay terminal 2 - Body ground Always 11 to 14 V
      Headlight relay terminal 3 - Body ground Always 11 to 14 V

    NG

    REPAIR OR REPLACE HARNESS OR CONNECTOR

    OK

  6. CHECK HARNESS AND CONNECTOR (HEADLIGHT RELAY [H-LP] - FUSE)


    1. A01IU4KE04
      Text in Illustration
      *1 Engine Room No. 1 Relay Block, Junction Block
      *2 Headlight Relay (H-LP)
      *3 H-LP LH LO Fuse
      *4 H-LP RH LO Fuse

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

      Standard Resistance
      Tester Connection Condition Specified Condition
      Headlight relay terminal 5 - H-LP LH LO fuse terminal Always Below 1 Ω
      Headlight relay terminal 5 - H-LP RH LO fuse terminal Always Below 1 Ω

    NG

    REPAIR OR REPLACE HARNESS OR CONNECTOR

    OK

  7. CHECK HARNESS AND CONNECTOR (HEADLIGHT RELAY [H-LP] - MAIN BODY ECU)


    1. Disconnect the H79 main body ECU connector.

      A01ISX0E02

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

      Standard Resistance
      Tester Connection Condition Specified Condition
      Headlight relay terminal 1 - H79-20 (HRLY) Always Below 1 Ω
      H79-20 (HRLY) - Body ground Always 10 kΩ or higher
      Text in Illustration
      *1

      Front view of wire harness connector

      (to Main Body ECU)

      		 *2 Engine Room No. 1 Relay Block, Junction Block
      *3 Headlight Relay (H-LP) - -

    NG

    REPAIR OR REPLACE HARNESS OR CONNECTOR

    OK

    REPLACE MAIN BODY ECU (INSTRUMENT PANEL JUNCTION BLOCK ASSEMBLY)