Lexus RX (RX 350L, RX450h) 2016-2024 Repair Manual: Check Bus 2 Line for Short to +B

Lexus RX (RX 350L, RX450h) 2016-2024 Repair Manual / Power Source & Network / Networking / Can Communication System / Check Bus 2 Line for Short to +B

DESCRIPTION

There may be a short circuit between one of the CAN bus lines and +B when no resistance exists between terminal 18 (CA4H) of the network gateway ECU and terminal 16 (BAT) of the DLC3, or terminal 17 (CA4L) of the network gateway ECU and terminal 16 (BAT) of the DLC3.

Symptom

Trouble Area

No resistance exists between terminal 18 (CA4H) of the network gateway ECU and terminal 16 (BAT) of the DLC3, or terminal 17 (CA4L) of the network gateway ECU and terminal 16 (BAT) of the DLC3.
  • Short in CAN main bus line
  • Short in CAN branch line
  • Network gateway ECU
  • ECM

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: Drive the vehicle at a speed of 60 km/h (37 mph) or more for 5 minutes or more. And drive the vehicle with the dynamic radar cruise control system operated for 4 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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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 SHORT TO +B IN CAN BUS LINE (NETWORK GATEWAY ECU)

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

(b) Disconnect the J75 network gateway ECU connector.

*A

for DLC3 Connector Type A

*B

for DLC3 Connector Type B

*1

DLC3

-

-

*a

Front view of wire harness connector

(to Network Gateway ECU)

-

-

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

Standard Resistance:

for DLC3 Connector Type A

Tester Connection

Condition

Specified Condition

J75-18 (CA4H) - J12-16 (BAT)

Cable disconnected from negative (-) battery terminal

6 kΩ or higher

J75-17 (CA4L) - J12-16 (BAT)
for DLC3 Connector Type B

Tester Connection

Condition

Specified Condition

J75-18 (CA4H) - J141-16 (BAT)

Cable disconnected from negative (-) battery terminal

6 kΩ or higher

J75-17 (CA4L) - J141-16 (BAT)
OK

REPLACE NETWORK GATEWAY ECU

NG

2.

CHECK FOR SHORT TO +B IN CAN BUS LINE (ECM)

(a) Reconnect the J75 network gateway ECU connector.

(b) Disconnect the A37 ECM connector.

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

*A

for DLC3 Connector Type A

*B

for DLC3 Connector Type B

*1

DLC3

-

-

*a

Front view of wire harness connector

(to ECM)

-

-

Standard Resistance:

for DLC3 Connector Type A

Tester Connection

Condition

Specified Condition

A37-13 (CANH) - J12-16 (BAT)

Cable disconnected from negative (-) battery terminal

6 kΩ or higher

A37-26 (CANL) - J12-16 (BAT)
for DLC3 Connector Type B

Tester Connection

Condition

Specified Condition

A37-13 (CANH) - J141-16 (BAT)

Cable disconnected from negative (-) battery terminal

6 kΩ or higher

A37-26 (CANL) - J141-16 (BAT)
OK

REPLACE ECM

NG

REPAIR OR REPLACE CAN MAIN BUS LINE OR CONNECTOR (ECM - NETWORK GATEWAY ECU)
    Check Bus 2 Lines for Short Circuit
    DESCRIPTION There may be a short circuit between the bus 2 main lines and/or bus 2 branch lines when the resistance between terminals 18 (CA4H) and 17 (CA4L) of the network gateway ECU is below 54 Ω. ...

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