Toyota Corolla Cross: ECUB Circuit Short to Ground or Open (B242F14)

Toyota Corolla Cross (2022-2024) Service Manual / Vehicle Exterior / Lighting (ext) / Lighting System (w/ Afs) / ECUB Circuit Short to Ground or Open (B242F14)

DESCRIPTION

The headlight ECU sub-assembly operates using the power source voltage input from the IGR terminal and ECUB terminal.

The power source voltage of the ECUB terminal is supplied when the main body ECU (multiplex network body ECU) turns the ECUB power supply relay (H-LP LH relay and H-LP RH relay) to ON.

The headlight ECU sub-assembly compares the power source voltage supply condition of the IGR terminal and ECUB terminal and monitors the result.

DTC No.	Detection Item	DTC Detection Condition	Trouble Area
B242F14	ECUB Circuit Short to Ground or Open	Detection condition: The ignition switch is ON Malfunction status: No power source voltage supplied to ECUB terminal while power source voltage being supplied to IGR terminal Malfunction duration: 10 seconds or more	Headlight ECU sub-assembly LH Harness or connector H-LP LH relay Power distribution box assembly Main body ECU (multiplex network body ECU)

DTC No.

Detection Item

DTC Detection Condition

Trouble Area

B242F14

ECUB Circuit Short to Ground or Open

Detection condition:

The ignition switch is ON

Malfunction status:

No power source voltage supplied to ECUB terminal while power source voltage being supplied to IGR terminal

Malfunction duration:

10 seconds or more

Headlight ECU sub-assembly LH
Harness or connector
H-LP LH relay
Power distribution box assembly
Main body ECU (multiplex network body ECU)

DTC No.	Detection Item	DTC Detection Condition	Trouble Area
B242F14	ECUB Circuit Short to Ground or Open	Detection condition: The ignition switch is ON Malfunction status: No power source voltage supplied to ECUB terminal while power source voltage being supplied to IGR terminal Malfunction duration: 10 seconds or more	Headlight ECU sub-assembly RH Harness or connector H-LP RH relay Power distribution box assembly Main body ECU (multiplex network body ECU)

DTC No.

Detection Item

DTC Detection Condition

Trouble Area

B242F14

ECUB Circuit Short to Ground or Open

Detection condition:

The ignition switch is ON

Malfunction status:

No power source voltage supplied to ECUB terminal while power source voltage being supplied to IGR terminal

Malfunction duration:

10 seconds or more

Headlight ECU sub-assembly RH
Harness or connector
H-LP RH relay
Power distribution box assembly
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 procedure.
Before replacing the main body ECU (multiplex network body ECU), refer to Registration.
If the headlight ECU sub-assembly LH has been replaced, it is necessary to synchronize the vehicle information and initialize the headlight ECU sub-assembly LH.
Click here

PROCEDURE

CLEAR DTC

(a) Clear the DTCs.

Body Electrical > Headlight Control > Clear DTCs Body Electrical > Headlight Control (Sub) > Clear DTCs

2.	CHECK FOR DTC

(a) Turn the ignition switch to ON.

(b) Wait 10 seconds or more.

Body Electrical > Headlight Control > Trouble Codes Body Electrical > Headlight Control (Sub) > Trouble Codes

OK:

DTC B242F14 is not output.

Result	Proceed to
OK	A
NG (DTC output from headlight ECU sub-assembly LH)	B
NG (DTC output from headlight ECU sub-assembly RH)	C

USE SIMULATION METHOD TO CHECK

GO TO STEP 10

3.	CHECK HARNESS AND CONNECTOR (HEADLIGHT ECU SUB-ASSEMBLY LH - BATTERY)

*a	Front view of wire harness connector (to Headlight ECU Sub-assembly LH)

(a) Disconnect the headlight ECU sub-assembly LH connector.

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

Standard Voltage:

Tester Connection	Switch Condition	Specified Condition
A159-13 (ECUB) - Body ground	Ignition switch ON	11 to 14 V

GO TO STEP 5

4.	CHECK HARNESS AND CONNECTOR (HEADLIGHT ECU SUB-ASSEMBLY LH - BODY GROUND)

(a) Disconnect the headlight ECU sub-assembly LH connector.

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

Standard Resistance:

Tester Connection	Condition	Specified Condition
A159-12 (GND) - Body ground	Always	Below 1 Ω

*a	Front view of wire harness connector (to Headlight ECU Sub-assembly LH)

REPLACE HEADLIGHT ECU SUB-ASSEMBLY LH

REPAIR OR REPLACE HARNESS OR CONNECTOR

5.	INSPECT H-LP LH RELAY

Click here

REPLACE H-LP LH RELAY

6.	CHECK HARNESS AND CONNECTOR (H-LP LH RELAY - HEADLIGHT ECU SUB-ASSEMBLY LH)

(a) Remove the H-LP LH relay.

(b) Disconnect the A159 headlight ECU sub-assembly LH connector.

Standard Resistance:

Tester Connection	Condition	Specified Condition
3 (H-LP LH relay) - A159-13 (ECUB)	Always	Below 1 Ω
3 (H-LP LH relay) - Body ground	Always	10 kΩ or higher
A159-13 (ECUB) - Body ground	Always	10 kΩ or higher

REPAIR OR REPLACE HARNESS OR CONNECTOR

7.	CHECK HARNESS AND CONNECTOR (H-LP LH RELAY - BATTERY)

(a) Remove the H-LP LH relay.

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

Standard Voltage:

Tester Connection	Switch Condition	Specified Condition
2 (H-LP LH relay) - Body ground	Ignition switch off	11 to 14 V
5 (H-LP LH relay) - Body ground	Ignition switch off	11 to 14 V

*a	Front view of wire harness connector (to H-LP LH Relay)

REPAIR OR REPLACE HARNESS OR CONNECTOR

8.	CHECK HARNESS AND CONNECTOR (H-LP LH RELAY - POWER DISTRIBUTION BOX ASSEMBLY)

(a) Remove the H-LP LH relay.

(b) Disconnect the 8E power distribution box assembly connector.

Standard Resistance:

Tester Connection	Condition	Specified Condition
1 (H-LP LH relay) - 8E-6	Always	Below 1 Ω
1 (H-LP LH relay) - Body ground	Always	10 kΩ or higher
8E-6 - Body ground	Always	10 kΩ or higher

REPAIR OR REPLACE HARNESS OR CONNECTOR

9.	INSPECT POWER DISTRIBUTION BOX ASSEMBLY

Component without harness connected

(Power Distribution Box Assembly)

(a) Remove the power distribution box assembly.

Click here

(b) Remove the main body ECU (multiplex network body ECU) from the power distribution box assembly.

Standard Resistance:

Tester Connection	Condition	Specified Condition
8E-6 - MB-8 (HRLY)	Always	Below 1 Ω

REPLACE MAIN BODY ECU (MULTIPLEX NETWORK BODY ECU)

REPLACE POWER DISTRIBUTION BOX ASSEMBLY

10.	CHECK HARNESS AND CONNECTOR (HEADLIGHT ECU SUB-ASSEMBLY RH - BATTERY)

*a	Front view of wire harness connector (to Headlight ECU Sub-assembly RH)

(a) Disconnect the headlight ECU sub-assembly RH connector.

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

Standard Voltage:

Tester Connection	Switch Condition	Specified Condition
A160-13 (ECUB) - Body ground	Ignition switch ON	11 to 14 V

GO TO STEP 12

11.	CHECK HARNESS AND CONNECTOR (HEADLIGHT ECU SUB-ASSEMBLY RH - BODY GROUND)

(a) Disconnect the headlight ECU sub-assembly RH connector.

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

Standard Resistance:

Tester Connection	Condition	Specified Condition
A160-12 (GND) - Body ground	Always	Below 1 Ω

*a	Front view of wire harness connector (to Headlight ECU Sub-assembly RH)

REPLACE HEADLIGHT ECU SUB-ASSEMBLY RH

REPAIR OR REPLACE HARNESS OR CONNECTOR

12.	INSPECT H-LP RH RELAY

Click here

REPLACE H-LP RH RELAY

13.	CHECK HARNESS AND CONNECTOR (H-LP RH RELAY - HEADLIGHT ECU SUB-ASSEMBLY RH)

(a) Remove the H-LP RH relay.

(b) Disconnect the A160 headlight ECU sub-assembly RH connector.

Standard Resistance:

Tester Connection	Condition	Specified Condition
3 (H-LP RH relay) - A160-13 (ECUB)	Always	Below 1 Ω
3 (H-LP RH relay) - Body ground	Always	10 kΩ or higher
A160-13 (ECUB) - Body ground	Always	10 kΩ or higher

REPAIR OR REPLACE HARNESS OR CONNECTOR

14.	CHECK HARNESS AND CONNECTOR (H-LP RH RELAY - BATTERY)

(a) Remove the H-LP RH relay.

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

Standard Voltage:

Tester Connection	Switch Condition	Specified Condition
2 (H-LP RH relay) - Body ground	Ignition switch off	11 to 14 V
5 (H-LP RH relay) - Body ground	Ignition switch off	11 to 14 V

*a	Front view of wire harness connector (to H-LP RH Relay)

REPAIR OR REPLACE HARNESS OR CONNECTOR

15.	CHECK HARNESS AND CONNECTOR (H-LP RH RELAY - POWER DISTRIBUTION BOX ASSEMBLY)

(a) Remove the H-LP RH relay.

(b) Disconnect the 4E power distribution box assembly connector.

Standard Resistance:

Tester Connection	Condition	Specified Condition
1 (H-LP RH relay) - 4E-10	Always	Below 1 Ω
1 (H-LP RH relay) - Body ground	Always	10 kΩ or higher
4E-10 - Body ground	Always	10 kΩ or higher

REPAIR OR REPLACE HARNESS OR CONNECTOR

16.	INSPECT POWER DISTRIBUTION BOX ASSEMBLY

Component without harness connected

(Power Distribution Box Assembly)

(a) Remove the power distribution box assembly.

Click here

(b) Remove the main body ECU (multiplex network body ECU) from the power distribution box assembly.

Standard Resistance:

Tester Connection	Condition	Specified Condition
8E-10 - MB-9 (HRLY2)	Always	Below 1 Ω

REPLACE MAIN BODY ECU (MULTIPLEX NETWORK BODY ECU)

REPLACE POWER DISTRIBUTION BOX ASSEMBLY

SEE MORE:

System Diagram

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Toyota Corolla Cross: ECUB Circuit Short to Ground or Open (B242F14)

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