Toyota Yaris: Lighting System / Light Sensor Circuit Malfunction (B124400)

Toyota Yaris XP210 (2020-2024) Reapir and Service Manual / Vehicle Exterior / Lighting (ext) / Lighting System / Light Sensor Circuit Malfunction (B124400)

DESCRIPTION

The automatic light control sensor detects ambient light. The sensor creates an electrical signal based on the amount of light detected, and sends the signal to the main body ECU (multiplex network body ECU). The main body ECU (multiplex network body ECU) turns on or off the headlights and taillights according to the signal.

DTC No.

Detection Item

DTC Detection Condition

Trouble Area

B124400

Light Sensor Circuit Malfunction

  • The ignition switch is to ON.
  • Either of the following conditions is met:
    • Malfunction in automatic light control sensor
    • Open or short in automatic light control sensor circuit
  • 5 seconds or more
  • Automatic light control sensor
  • Harness or connector
  • Main body ECU (multiplex network body ECU)

WIRING DIAGRAM

CAUTION / NOTICE / HINT

NOTICE:

Before replacing the main body ECU (multiplex network body ECU), refer to Registration.

Click here

PROCEDURE

1.

CLEAR DTC

(a) Clear the DTCs.

Body Electrical > Main Body > Clear DTCs
NEXT

2.

CHECK FOR DTC

(a) Turn the ignition switch to ON.

(b) Wait 10 seconds or more.

(c) Turn the GTS on.

(d) Enter the following menus: Body Electrical / Main Body / Trouble Codes.

(e) Check for DTCs.

Body Electrical > Main Body > Trouble Codes

Result

Proceed to

B124400 is output

A

B124400 is not output

B

B

USE SIMULATION METHOD TO CHECK

A

3.

READ VALUE USING GTS

(a) According to the display on the GTS, read the Data List and check that the value of Light Sensor Illuminance changes while performing the following:

(1) Cover the automatic light control sensor with an opaque object.

(2) Slowly move the opaque object to uncover and then cover the automatic light control sensor.

Body Electrical > Main Body > Data List

Tester Display

Measurement Item

Range

Normal Condition

Diagnostic Note

Light Sensor Illuminance

Light control sensor illuminance

0 to 8191 lx or Sensor Fail

Value is output according to ambient light level

The displayed value is "0" when no light is detected.

Body Electrical > Main Body > Data List

Tester Display

Light Sensor Illuminance

OK:

The value changes according to the amount the automatic light control sensor is covered.

OK

REPLACE MAIN BODY ECU (MULTIPLEX NETWORK BODY ECU)

NG

4.

CHECK HARNESS AND CONNECTOR (AUTOMATIC LIGHT CONTROL SENSOR - MAIN BODY ECU (MULTIPLEX NETWORK BODY ECU))

(a) Disconnect the H78 automatic light control sensor connector.

(b) Disconnect the H4 main body ECU (multiplex network body ECU) connector.

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

Standard Resistance:

Tester Connection

Condition

Specified Condition

H78-1 (CLTB) - H4-8 (CLTB)

Always

Below 1 Ω

H78-4 (CLTS) - H4-20 (CLTS)

Always

Below 1 Ω

H78-2 (CLTE) - H4-21 (CLTE)

Always

Below 1 Ω

H78-1 (CLTB) or H4-8 (CLTB) - Body ground

Always

10 kΩ or higher

H78-4 (CLTS) or H4-20 (CLTS) - Body ground

Always

10 kΩ or higher

H78-2 (CLTE) or H4-21 (CLTE) - Body ground

Always

10 kΩ or higher

NG

REPAIR OR REPLACE HARNESS OR CONNECTOR

OK

5.

INSPECT MAIN BODY ECU (MULTIPLEX NETWORK BODY ECU)

*a

Component with harness connected

(Main Body ECU (Multiplex Network Body ECU))

(a) Connect the H4 main body ECU (multiplex network body ECU) connector.

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

Standard Voltage:

Tester Connection

Switch Condition

Specified Condition

H4-8 (CLTB) - H4-21 (CLTE)

Ignition switch off

Below 1 V

H4-8 (CLTB) - H4-21 (CLTE)

Ignition switch ON

11 to 14 V

NG

REPLACE MAIN BODY ECU (MULTIPLEX NETWORK BODY ECU)

OK

6.

INSPECT AUTOMATIC LIGHT CONTROL SENSOR

Click here

OK

REPLACE MAIN BODY ECU (MULTIPLEX NETWORK BODY ECU)

NG

REPLACE AUTOMATIC LIGHT CONTROL SENSOR

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