Lexus RX (RX 350L, RX450h) 2016-2025 Repair Manual: Main Body ECU Communication Stop Mode

Lexus RX (RX 350L, RX450h) 2016-2025 Repair Manual / Power Source & Network / Networking / Can Communication System / Main Body ECU Communication Stop Mode

DESCRIPTION

Detection Item

Symptom

Trouble Area

Main Body ECU Communication Stop Mode

Either condition is met:

  • "Main Body" is not displayed on the CAN Bus Check screen of the Techstream.

    Click here

  • Communication system DTCs (DTCs that start with U) that correspond to "Main Body ECU Communication Stop Mode" in "DTC Combination Table" are output.

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  • Main body ECU (multiplex network body ECU) branch line or connector
  • Power source circuit of main body ECU (multiplex network body ECU) or instrument panel junction block assembly
  • Main body ECU (multiplex network body ECU) or instrument panel junction block assembly ground circuit
  • Main body ECU (multiplex network body ECU) or instrument panel junction block assembly

WIRING DIAGRAM

CAUTION / NOTICE / HINT

NOTICE:

  • Before measuring the resistance of the CAN bus, turn the engine switch off and leave the vehicle for 1 minute or more without operating the key or any switches, or opening or closing the doors. After that, disconnect the cable from the negative (-) battery terminal and leave the vehicle for 1 minute or more before measuring the resistance.
  • After turning the engine switch off, waiting time may be required before disconnecting the cable from the negative (-) battery terminal. Therefore, make sure to read the disconnecting the cable from the negative (-) battery terminal notices before proceeding with work.

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  • Because the order of diagnosis is important to allow correct diagnosis, make sure to begin troubleshooting using How to Proceed with Troubleshooting when CAN communication system related DTCs are output.

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  • After performing repairs, perform the DTC check procedure and confirm that the DTCs are not output again.
  • DTC check procedure: Turn the engine switch on (IG) and wait for at least 20 seconds. Drive the vehicle at a speed of 5 km/h (3 mph) or more for 7 seconds or more.
  • After the repair, perform the CAN bus check and check that all the ECUs and sensors connected to the CAN communication system are displayed.

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  • Inspect the fuses for circuits related to this system before performing the following procedure.
  • If the main body ECU (multiplex network body ECU) is replaced, refer to Registration.

    Click here

HINT:

  • Operating the engine switch, any other switches or a door triggers related ECU and sensor communication on the CAN. This communication will cause the resistance value to change.
  • Even after DTCs are cleared, if a DTC is stored again after driving the vehicle for a while, the malfunction may be occurring due to vibration of the vehicle. In such a case, wiggling the ECUs or wire harness while performing the inspection below may help determine the cause of the malfunction.

PROCEDURE

1.

CHECK FOR OPEN IN CAN BUS LINES (MAIN BODY ECU (MULTIPLEX NETWORK BODY ECU) BRANCH LINE)

(a) Disconnect the cable from the negative (-) battery terminal.

(b) Disconnect the J8 main body ECU (multiplex network body ECU) connector.

*a

Front view of wire harness connector

(to Main Body ECU (Multiplex Network Body ECU))

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

Standard Resistance:

Tester Connection

Condition

Specified Condition

J8-14 (CANH) - J8-13 (CANL)

Cable disconnected from negative (-) battery terminal

54 to 69 Ω
NG

REPAIR OR REPLACE CAN BRANCH LINES OR CONNECTOR (MAIN BODY ECU (MULTIPLEX NETWORK BODY ECU))
OK

2.

CHECK HARNESS AND CONNECTOR (POWER SOURCE CIRCUIT)

(a) Remove the main body ECU (multiplex network body ECU).

Click here

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

Standard Resistance:

Tester Connection

Condition

Specified Condition

MB-11 (GND1) - Body ground

Cable disconnected from negative (-) battery terminal

Below 1 Ω

*1

Instrument Panel Junction Block Assembly

(c) Reconnect the cable to the negative (-) battery terminal.

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

Standard Voltage:

Tester Connection

Condition

Specified Condition

MB-30 (ACC) - Body ground

Engine switch on (ACC)

11 to 14 V

MB-31 (BECU) - Body ground

Always

11 to 14 V

MB-32 (IG) - Body ground

Engine switch on (IG)

11 to 14 V

Result

Proceed to

OK

A

NG (BECU)

B

NG (ACC)

C

NG (IG)

D

NG (GND1)

E
A

REPLACE MAIN BODY ECU (MULTIPLEX NETWORK BODY ECU)

C

GO TO LIGHTING (INT) SYSTEM (ACC SIGNAL CIRCUIT)

D

GO TO LIGHTING (INT) SYSTEM (IG SIGNAL CIRCUIT)

E

GO TO STEP 4

B

3.

CHECK HARNESS AND CONNECTOR (BECU SIGNAL CIRCUIT)

(a) Disconnect the 2C instrument panel junction block assembly connector.

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

Standard Voltage:

Tester Connection

Condition

Specified Condition

2C-1 - Body ground

Always

11 to 14 V

*a

Front view of wire harness connector

(to Instrument Panel Junction Block Assembly)
OK

REPLACE INSTRUMENT PANEL JUNCTION BLOCK ASSEMBLY

NG

REPAIR OR REPLACE HARNESS OR CONNECTOR (BECU SIGNAL CIRCUIT)

4.

CHECK HARNESS AND CONNECTOR (GROUND CIRCUIT)

(a) Disconnect the cable from the negative (-) battery terminal.

(b) Disconnect the 2B instrument panel junction block assembly connector.

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

Standard Resistance:

Tester Connection

Condition

Specified Condition

2B-3 - Body ground

Cable disconnected from negative (-) battery terminal

Below 1 Ω

*a

Front view of wire harness connector

(to Instrument Panel Junction Block Assembly)
OK

REPLACE INSTRUMENT PANEL JUNCTION BLOCK ASSEMBLY

NG

REPAIR OR REPLACE HARNESS OR CONNECTOR (GROUND CIRCUIT)
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