Lexus RX (RX 350L, RX450h) 2016-2025 Repair Manual: Communication Malfunction between ECUs Connected by LIN (B2785)

Lexus RX (RX 350L, RX450h) 2016-2025 Repair Manual / Power Source & Network / Networking / Lin Communication System / Communication Malfunction between ECUs Connected by LIN (B2785)

DESCRIPTION

If the certification ECU (smart key ECU assembly) detects a communication error with an ECU connected to the certification bus lines for 7 sedonds or more, DTC B2785 will be stored.

DTC No.

Detection Item

DTC Detection Condition

Trouble Area

B2785

Communication Malfunction between ECUs Connected by LIN
  • Errors in LIN communication between ECUs or an open or short in communication lines.
  • The certification ECU (smart key ECU assembly) detects a communication error with an ECU connected to the certification bus lines for 7 sedonds or more.
  • Certification ECU (smart key ECU assembly)
  • Steering lock ECU (steering lock actuator or upper bracket assembly)
  • ID code box (immobiliser code ECU)
  • Wire harness or connector
  • AM2 fuse
  • STRG LOCK fuse
  • ECU-B NO. 3 fuse

WIRING DIAGRAM

CAUTION / NOTICE / HINT

NOTICE:

  • Inspect the fuses for circuits related to this system before performing the following procedure.
  • If the certification ECU (smart key ECU assembly), ID code box (immobiliser code ECU) and steering lock ECU (steering lock actuator or upper bracket assembly) is replaced, refer to Registration.

    Click here

  • Before performing the inspection, check that DTC B2786, B2789 or B278C is not output.

    Click here

  • When using the Techstream with the engine switch off, connect the Techstream to the DLC3 and turn a courtesy light switch on and off at intervals of 1.5 seconds or less until communication between the Techstream and the vehicle begins. Then select Model Code "KEY REGIST" under manual mode and enter the following menus: Body Electrical / Smart Access(CAN). While using the Techstream, periodically turn a courtesy light switch on and off at intervals of 1.5 seconds or less to maintain communication between the Techstream and the vehicle.

PROCEDURE

1.

CHECK HARNESS AND CONNECTOR (CERTIFICATION ECU (SMART KEY ECU ASSEMBLY) - EACH ECU)

(a) Disconnect the J41 certification ECU (smart key ECU assembly) connector.

(b) Disconnect the L1 steering lock ECU (steering lock actuator or upper bracket assembly) connector.

(c) Disconnect the J36 ID code box (immobiliser code ECU) connector.

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

NOTICE:

Make sure that each ECU is in sleep mode before performing the inspection. To enter sleep mode, turn the engine switch from on (IG) to off and wait for 180 seconds or more without operating any switches.

Standard Resistance:

Tester Connection

Condition

Specified Condition

J41-13 (LIN) - J36-2 (LIN1)

Engine switch off

Below 1 Ω

J41-13 (LIN) - L1-5 (LIN)

Engine switch off

Below 1 Ω

J41-13 (LIN), L1-5 (LIN) or J36-2 (LIN1) - Body ground

Engine switch off

10 kΩ or higher
NG

REPAIR OR REPLACE HARNESS OR CONNECTOR
OK

2.

CHECK FOR DTC (STEERING LOCK ECU (STEERING LOCK ACTUATOR OR UPPER BRACKET ASSEMBLY))

(a) Reconnect the J41 certification ECU (smart key ECU assembly) connector.

(b) Reconnect the J36 ID code box (immobiliser code ECU) connector.

(c) Clear the DTCs.

Click here

Body Electrical > Smart Access > Clear DTCs

(d) Recheck for DTCs.

Body Electrical > Smart Access > Trouble Codes

Result

Proceed to

DTC B2785 is output

A

DTC B2785 is not output

B
B

REPLACE STEERING LOCK ECU (STEERING LOCK ACTUATOR OR UPPER BRACKET ASSEMBLY)

A

3.

CHECK FOR DTC (ID CODE BOX (IMMOBILISER CODE ECU))

(a) Reconnect the L1 steering lock ECU (steering lock actuator or upper bracket assembly) connector.

(b) Disconnect the J36 ID code box (immobiliser code ECU) connector.

(c) Clear the DTCs.

Click here

Body Electrical > Smart Access > Clear DTCs

(d) Recheck for DTCs.

Body Electrical > Smart Access > Trouble Codes

Result

Proceed to

DTC B2785 is output

A

DTC B2785 is not output

B
A

REPLACE CERTIFICATION ECU (SMART KEY ECU ASSEMBLY)

B

REPLACE ID CODE BOX (IMMOBILISER CODE ECU)

    Lost Communication with Sliding Sunshade ECU (B2329)
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    No Response from Steering Lock ECU (B2786)
    DESCRIPTION This DTC is stored when LIN communication between the certification ECU (smart key ECU assembly) and steering lock ECU (steering lock actuator or upper bracket assembly) stops for 10 secon ...

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