Lexus NX manuals

Lexus NX: Check Bus 3 Lines for Short Circuit

Lexus NX Service Manual / Power Source & Network / Networking / Can Communication System / Check Bus 3 Lines for Short Circuit

DESCRIPTION

There may be a short circuit between the CAN main bus lines and/or CAN branch lines when the resistance between terminals 6 (CA3H) and 21 (CA3L) of the central gateway ECU (network gateway ECU) is below 54 Ω.

Symptom

Trouble Area
*1: w/ Telematics Transceiver

*2: w/ Bus Buffer ECU
  • Resistance between terminals 6 (CA3H) and 21 (CA3L) of the central gateway ECU (network gateway ECU) is below 54 Ω.
  • Resistance between terminals 19 (CAYH) and 20 (CAYL) of the central gateway ECU (network gateway ECU) is below 54 Ω.
  • Short in CAN main bus wire
  • Short in CAN branch wire
  • Central gateway ECU (network gateway ECU)
  • DCM (telematics transceiver)*1
  • Bus buffer ECU*2
  • Radio receiver assembly
  • No. 10 CAN junction connector

WIRING DIAGRAM

CAUTION / NOTICE / HINT

CAUTION:

When performing the confirmation driving pattern, obey all speed limits and traffic laws.

NOTICE:

  • Before measuring the resistance of the CAN bus, turn the power 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 (-) auxiliary battery terminal and leave the vehicle for 1 minute or more before measuring the resistance.
  • After turning the power switch off, waiting time may be required before disconnecting the cable from the negative (-) auxiliary battery terminal.

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  • When disconnecting and reconnecting the auxiliary battery.

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    HINT:

    When disconnecting and reconnecting the auxiliary battery, there is an automatic learning function that completes learning when the respective system is used.

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  • Some parts must be initialized and set when replacing or removing and installing parts.

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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 power switch on (IG) and wait for 1 minute or more. Then operate the suspected malfunctioning system and drive the vehicle at 60 km/h (37 mph) or more for 5 minutes 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 as normal.

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  • The following malfunctions may occur if a radio receiver assembly from another vehicle is installed to this vehicle. Therefore, when replacing the radio receiver assembly, be sure to replace it with new one.
    • Communication malfunction DTC is output
    • Does not operate normally

HINT:

  • Operating the power switch, any switches or any doors triggers related ECU and sensor communication with the CAN, which causes resistance variation.
  • 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 IN CAN BUS WIRES (NO. 10 CAN JUNCTION CONNECTOR)

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

(b) Disconnect the No. 10 CAN junction connector.

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

Standard Resistance:

Tester Connection

Condition

Specified Condition

Connected to
*1: w/ Telematics Transceiver

*2: w/ Bus Buffer ECU

I164-1 (CANH) - I164-12 (CANL)

Cable disconnected from negative (-) auxiliary battery terminal

108 to 132 Ω

Central gateway ECU (network gateway ECU)

I164-2 (CANH) - I164-13 (CANL)

Cable disconnected from negative (-) auxiliary battery terminal

200 Ω or higher

Radio receiver assembly

I164-3 (CANH) - I164-14 (CANL)

Cable disconnected from negative (-) auxiliary battery terminal

200 Ω or higher

DCM (telematics transceiver)*1

I164-4 (CANH) - I164-15 (CANL)

Cable disconnected from negative (-) auxiliary battery terminal

200 Ω or higher

Bus buffer ECU*2

I164-5 (CANH) - I164-16 (CANL)

Cable disconnected from negative (-) auxiliary battery terminal

108 to 132 Ω

Central gateway ECU (network gateway ECU)

*a

Front view of wire harness connector

(to No. 10 CAN Junction Connector)

*b

to Central Gateway ECU (Network Gateway ECU)

*c

to Radio Receiver Assembly

*d

to DCM (Telematics Transceiver) (w/ Telematics Transceiver)

*e

to Bus Buffer ECU (w/ Bus Buffer ECU)

*f

to Central Gateway ECU (Network Gateway ECU)

Result

Proceed to

OK

A

NG (Central gateway ECU [network gateway ECU] CAN main wire)

B

NG (Wire to ECU or sensor)

C
A

REPLACE NO. 10 CAN JUNCTION CONNECTOR
C

GO TO STEP 4

B

2.

CONNECT CONNECTOR

(a) Reconnect the I164 No. 10 CAN junction connector.

NEXT

3.

CHECK FOR SHORT IN CAN BUS WIRES (CENTRAL GATEWAY ECU [NETWORK GATEWAY ECU] - NO. 10 CAN JUNCTION CONNECTOR)

(a) Disconnect the central gateway ECU (network gateway ECU) connector.

*a

Front view of wire harness connector

(to Central Gateway ECU [Network Gateway ECU])

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

Standard Resistance:

Tester Connection

Condition

Specified Condition

I160-6 (CA3H) - I160-21 (CA3L)

Cable disconnected from negative (-) auxiliary battery terminal

200 Ω or higher

I160-19 (CAYH) - I160-20 (CAYL)
OK

REPLACE CENTRAL GATEWAY ECU (NETWORK GATEWAY ECU)

NG

REPLACE CAN BUS MAIN WIRE OR CONNECTOR (CENTRAL GATEWAY ECU [NETWORK GATEWAY ECU] - NO. 10 CAN JUNCTION CONNECTOR)

4.

CHECK FOR SHORT IN CAN BUS WIRES (ECU, SENSOR)

(a) Reconnect all wire harness connectors.

(b) Disconnect the connector that includes terminals CANH and CANL from the ECU or sensor to which the short circuited branch line is connected.

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

Standard Resistance:

Tester Connection

Condition

Specified Condition

I160-6 (CA3H) - I160-21 (CA3L)

Cable disconnected from negative (-) auxiliary battery terminal

54 to 69 Ω

HINT:

If the resistance becomes normal (between 54 and 69 Ω) when the connector is disconnected from the ECU or sensor, there may be a short in the ECU or sensor.

*a

Component with harness connected

(Central Gateway ECU [Network Gateway ECU])
OK

REPLACE ECU OR SENSOR
NG

REPAIR OR REPLACE HARNESS OR CONNECTOR

READ NEXT:

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DESCRIPTION When the CAN bus main lines are normal (no open, short to ground, short to +B or short between lines) and there is an ECU or sensor on the "Communication Bus Check" screen that is indicate

 Open in Bus 5 Main Bus Line

DESCRIPTION There may be an open circuit in one of the CAN main bus lines when the resistance between terminals 15 (CA5H) and 16 (CA5L) of the central gateway ECU (network gateway ECU) is 70 Ω or hig

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