Lexus RX (RX 350L, RX450h) 2016-2025 Repair Manual: Lost Communication With Headlamp Control Module "B" (U0242)

Lexus RX (RX 350L, RX450h) 2016-2025 Repair Manual / Vehicle Exterior / Lighting (ext) / Lighting System (w/ Automatic Headlight Beam Level Control System) / Lost Communication With Headlamp Control Module "B" (U0242)

DESCRIPTION

for Multiple Beam Headlight:
  • The No. 1 headlight ECU sub-assembly LH communicates with the No. 1 headlight ECU sub-assembly RH via CAN communication. If communication between the No. 1 headlight ECU sub-assembly LH and No. 1 headlight ECU sub-assembly RH stops, the No. 1 headlight ECU sub-assembly LH will store this DTC.
for Single Beam Headlight:
  • The No. 1 headlight ECU sub-assembly LH communicates with the No. 1 headlight ECU sub-assembly RH via LIN communication. If communication between the No. 1 headlight ECU sub-assembly LH and No. 1 headlight ECU sub-assembly RH stops, the No. 1 headlight ECU sub-assembly LH will store this DTC.
for Multiple Beam Headlight

DTC No.

Detection Item

DTC Detection Condition

Trouble Area

DTC Output from

U0242

Lost Communication With Headlamp Control Module "B"
  • The engine switch is on (IG).
  • A communication malfunction with the No. 1 headlight ECU sub-assembly RH is detected
  • 10 seconds or more
  • Harness or connector
  • No. 1 headlight ECU sub-assembly LH
  • No. 1 headlight ECU sub-assembly RH

AFS
for Single Beam Headlight

DTC No.

Detection Item

DTC Detection Condition

Trouble Area

DTC Output from

U0242

Lost Communication With Headlamp Control Module "B"
  • The engine switch is on (IG).
  • A communication malfunction with the No. 1 headlight ECU sub-assembly RH is detected
  • 10 seconds or more
  • Harness or connector
  • No. 1 headlight ECU sub-assembly LH
  • No. 1 headlight ECU sub-assembly RH

HL AutoLeveling
for Multiple Beam Headlight:

Pattern

DTC output part name

(Display on Techstream)

Suspected Area (Malfunction Status)

Headlight ECU Sub-assembly LH

(AFS)

U0242
○: DTC is output

Pattern 1

○
  • Open in CAN communication line (No. 1 headlight ECU sub-assembly LH - No. 1 headlight ECU sub-assembly RH)
  • Open or short in No. 1 headlight ECU sub-assembly LH internal circuit
  • Open or short in No. 1 headlight ECU sub-assembly RH internal circuit
for Single Beam Headlight:

Pattern

DTC output part name

(Display on Techstream)

Suspected Area (Malfunction Status)

Headlight ECU Sub-assembly LH

(HL AutoLeveling)

U0242
○: DTC is output

Pattern 1

○
  • Open in LIN communication line (No. 1 headlight ECU sub-assembly LH - No. 1 headlight ECU sub-assembly RH)
  • Open or short in No. 1 headlight ECU sub-assembly LH internal circuit
  • Open or short in No. 1 headlight ECU sub-assembly RH internal circuit

WIRING DIAGRAM

for Multiple Beam Headlight

for Single Beam Headlight

CAUTION / NOTICE / HINT

NOTICE:

  • If the No. 1 headlight ECU sub-assembly LH has been replaced, it is necessary to synchronize the vehicle information and initialize the No. 1 headlight ECU sub-assembly LH.

    Click here

  • If the headlight assembly LH has been replaced, it is necessary to synchronize the vehicle information and initialize the No. 1 headlight ECU sub-assembly LH.*

    Click here

  • When replacing the No. 1 headlight ECU sub-assembly LH, always replace it with a new one. If a No. 1 headlight ECU sub-assembly LH which was installed to another vehicle is used, the information stored in it will not match the information from the vehicle and a DTC may be stored.
  • When replacing the headlight assembly LH, always replace it with a new one. If a headlight assembly LH which was installed to another vehicle is used, the information stored in it will not match the information from the vehicle and a DTC may be stored.*
    • *: for TMMC Made

PROCEDURE

1.

CONFIRM MODEL

(a) Choose the model to be inspected.

Result

Proceed to

for Multiple Beam Headlight

A

for Single Beam Headlight

B
B

GO TO STEP 7

A

2.

CHECK FOR DTC

(a) Connect the Techstream to the DLC3.

(b) Turn the engine switch on (IG).

(c) Turn the Techstream on.

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

(e) Check for DTCs.

Body Electrical > AFS > Trouble Codes

OK:

DTC U0242 is not output.

OK

USE SIMULATION METHOD TO CHECK

NG

3.

CHECK HARNESS AND CONNECTOR (NO. 1 HEADLIGHT ECU SUB-ASSEMBLY LH - NO. 1 HEADLIGHT ECU SUB-ASSEMBLY RH)

(a) Disconnect the A49 No. 1 headlight ECU sub-assembly LH connector.

(b) Disconnect the A50 No. 1 headlight ECU sub-assembly RH connector.

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

Standard Resistance:

Tester Connection

Condition

Specified Condition

A49-22 (LCH) - A50-22 (LCH)

Always

Below 1 Ω

A49-21 (LCL) - A50-21 (LCL)

Always

Below 1 Ω

A49-22 (LCH) or A50-22 (LCH) - Body ground

Always

10 kΩ or higher

A49-21 (LCL) or A50-21 (LCL) - Body ground

Always

10 kΩ or higher
NG

REPAIR OR REPLACE HARNESS OR CONNECTOR
OK

4.

REPLACE NO. 1 HEADLIGHT ECU SUB-ASSEMBLY RH

(a) Replace the No. 1 headlight ECU sub-assembly RH with a new one.

Click here

NEXT

5.

CLEAR DTC

(a) Connect the Techstream to the DLC3.

(b) Turn the engine switch on (IG).

(c) Turn the Techstream on.

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

(e) Clear the DTCs.

Body Electrical > AFS > Clear DTCs
NEXT

6.

CHECK FOR DTC

(a) Connect the Techstream to the DLC3.

(b) Turn the engine switch on (IG).

(c) Turn the Techstream on.

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

(e) Check for DTCs.

Body Electrical > AFS > Trouble Codes

OK:

DTC U0242 is not output.

OK

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

REPLACE NO. 1 HEADLIGHT ECU SUB-ASSEMBLY LH

7.

CHECK FOR DTC

(a) Connect the Techstream to the DLC3.

(b) Turn the engine switch on (IG).

(c) Turn the Techstream on.

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

(e) Check for DTCs.

Body Electrical > HL AutoLeveling > Trouble Codes

OK:

DTC U0242 is not output.

OK

USE SIMULATION METHOD TO CHECK

NG

8.

CHECK HARNESS AND CONNECTOR (NO. 1 HEADLIGHT ECU SUB-ASSEMBLY LH - NO. 1 HEADLIGHT ECU SUB-ASSEMBLY RH)

(a) Disconnect the A49 No. 1 headlight ECU sub-assembly LH connector.

(b) Disconnect the A50 No. 1 headlight ECU sub-assembly RH connector.

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

Standard Resistance:

Tester Connection

Condition

Specified Condition

A49-20 (LINL) - A50-20 (LINL)

Always

Below 1 Ω

A49-20 (LINL) or A50-20 (LINL) - Body ground

Always

10 kΩ or higher
NG

REPAIR OR REPLACE HARNESS OR CONNECTOR
OK

9.

REPLACE NO. 1 HEADLIGHT ECU SUB-ASSEMBLY RH

(a) Replace the No. 1 headlight ECU sub-assembly RH with a new one.

Click here

NEXT

10.

CLEAR DTC

(a) Connect the Techstream to the DLC3.

(b) Turn the engine switch on (IG).

(c) Turn the Techstream on.

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

(e) Clear the DTCs.

Body Electrical > HL AutoLeveling > Clear DTCs
NEXT

11.

CHECK FOR DTC

(a) Connect the Techstream to the DLC3.

(b) Turn the engine switch on (IG).

(c) Turn the Techstream on.

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

(e) Check for DTCs.

Body Electrical > HL AutoLeveling > Trouble Codes

OK:

DTC U0242 is not output.

OK

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

REPLACE NO. 1 HEADLIGHT ECU SUB-ASSEMBLY LH

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