DTC U0242: Lost Communication With Headlamp Control Module "B" [12/2018 -]: Procedure

WARNING: This page is about a different car, the 2022 Toyota Prius, 2021 Toyota Prius, 2020 Toyota Prius, and 2019 Toyota Prius. However, it is still accessible from the selected car via links, so may be relevant.

CLEAR DTC

Connect the Techstream to the DLC3.
Turn the power switch on (IG).
Turn the Techstream on.
Enter the following menus: Body Electrical / AFS / Trouble Codes.

Clear the DTCs.

Body Electrical > AFS > Clear DTCs

Result

Proceed to
NEXT

Result:

See step 2

CHECK FOR DTC

Connect the Techstream to the DLC3.
Turn the power switch on (IG).
Turn the Techstream on.
Enter the following menus: Body Electrical / AFS / Trouble Codes.

Check for DTCs.

Body Electrical > AFS > Trouble Codes

DTC U0242 is not output.

Result

Proceed to
OK
NG

Result:

USE SIMULATION METHOD TO CHECK. Refer to HOW TO PROCEED WITH TROUBLESHOOTING [12/2018 - 07/2020] , or refer to HOW TO PROCEED WITH TROUBLESHOOTING [07/2020 - 06/2021] , or refer to HOW TO PROCEED WITH TROUBLESHOOTING [06/2021 -]

Result:

See step 3

CHECK CAN BUS LINE (MALFUNCTION CONFIRMATION)

Turn the power switch off.
Disconnect the cable from the negative (-) auxiliary battery terminal.
Disconnect the A65 No. 1 headlight ECU sub-assembly LH connector.

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

Standard Resistance

& Routing (A65)

(A65)

Tester Connection	Condition	Specified Condition	Result
A65-21 (LCL) - A65-22 (LCH)	Cable disconnected from negative (-) auxiliary battery terminal	108 to 132 Ω	132 Ω or more: Open circuit in main bus lines
A65-21 (LCL) - A65-22 (LCH)		108 to 132 Ω	Below 108 Ω: Short circuit between bus lines
A65-21 (LCL) - GND	Cable disconnected from negative (-) auxiliary battery terminal	200 Ω or higher	Below 200 Ω: LCL short to ground
A65-22 (LCH) - GND	Cable disconnected from negative (-) auxiliary battery terminal	200 Ω or higher	Below 200 Ω: LCH short to ground
A65-21 (LCL) - +B	Cable disconnected from negative (-) auxiliary battery terminal	6 kΩ or higher	Below 6 kΩ: LCL +B short
A65-22 (LCH) - +B	Cable disconnected from negative (-) auxiliary battery terminal	6 kΩ or higher	Below 6 kΩ: LCH +B short

Result

Result	Proceed to
OK	A
NG (Open circuit in main lines)	B
NG (Short circuit between main lines)	C
NG (Short to +B or ground)	D

Result:

REPLACE NO. 1 HEADLIGHT ECU SUB-ASSEMBLY LH. Refer to REMOVAL [12/2018 -]

Result:

See step 5

Result:

See step 6

Result:

See step 4

CHECK FOR OPEN IN CAN BUS MAIN LINES (NO. 1 HEADLIGHT ECU SUB-ASSEMBLY LH - NO. 1 HEADLIGHT ECU SUB-ASSEMBLY RH)

Connect the A65 No. 1 headlight ECU sub-assembly LH connector.
Disconnect the A66 No. 1 headlight ECU sub-assembly RH connector.

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

Standard Resistance

& Routing (A66)

(A66)

Tester Connection	Condition	Specified Condition
A66-21 (LCL) - A66-22 (LCH)	Cable disconnected from negative (-) auxiliary battery terminal	108 to 132 Ω

Result

Proceed to
OK
NG

Result:

See step 7

Result:

REPAIR OR REPLACE CAN BUS MAIN LINE OR CONNECTOR

CHECK FOR SHORT BETWEEN CAN BUS LINES (NO. 1 HEADLIGHT ECU SUB-ASSEMBLY LH - NO. 1 HEADLIGHT ECU SUB-ASSEMBLY RH)

Connect the A65 No. 1 headlight ECU sub-assembly LH connector.
Disconnect the A66 No. 1 headlight ECU sub-assembly RH connector.

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

Standard Resistance

& Routing (A66)

(A66)

Tester Connection	Condition	Specified Condition
A66-21 (LCL) - A66-22 (LCH)	Cable disconnected from negative (-) auxiliary battery terminal	108 to 132 Ω

Result

Proceed to
OK
NG

Result:

See step 7

Result:

REPAIR OR REPLACE CAN BUS MAIN LINE OR CONNECTOR

CHECK FOR FOR SHORT IN CAN BUS LINE (NO. 1 HEADLIGHT ECU SUB-ASSEMBLY LH - NO. 1 HEADLIGHT ECU SUB-ASSEMBLY RH)

Disconnect the A66 No. 1 headlight ECU sub-assembly RH connector.

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

Standard Resistance

& Routing (A66)

(A66)

Tester Connection	Condition	Specified Condition
A66-21 (LCL) - GND	Cable disconnected from negative (-) auxiliary battery terminal	200 Ω or higher
A66-22 (LCH) - GND	Cable disconnected from negative (-) auxiliary battery terminal	200 Ω or higher
A66-21 (LCL) - +B	Cable disconnected from negative (-) auxiliary battery terminal	6 kΩ or higher
A66-22 (LCH) - +B	Cable disconnected from negative (-) auxiliary battery terminal	6 kΩ or higher

Result

Proceed to
OK
NG

Result:

REPAIR OR REPLACE CAN BUS MAIN LINE OR CONNECTOR

Result:

See step 7

REPLACE NO. 1 HEADLIGHT ECU SUB-ASSEMBLY RH

Replace the No. 1 headlight ECU sub-assembly RH with a new or known good one.

Refer to REMOVAL [12/2018 -]

Result

Proceed to
NEXT

Result:

See step 8

CLEAR DTC

Connect the Techstream to the DLC3.
Turn the power switch on (IG).
Turn the Techstream on.
Enter the following menus: Body Electrical / AFS / Trouble Codes.

Clear the DTCs.

Body Electrical > AFS > Clear DTCs

Result

Proceed to
NEXT

Result:

See step 9

CHECK FOR DTC

Connect the Techstream to the DLC3.
Turn the power switch on (IG).
Turn the Techstream on.
Enter the following menus: Body Electrical / AFS / Trouble Codes.

Check for DTCs.

Body Electrical > AFS > Trouble Codes

DTC U0242 is not output.

Result

Proceed to
OK
NG

Result:

END (NO. 1 HEADLIGHT ECU SUB-ASSEMBLY RH WAS DEFECTIVE)

Result:

REPLACE NO. 1 HEADLIGHT ECU SUB-ASSEMBLY LH. Refer to REMOVAL [12/2018 -]