Lexus IS250 · Service Manual COMMUNICATION SYSTEM

Short in CAN Bus Lines

Circuit diagnosis

DESCRIPTION

The CAN bus lines are considered to be shorted when the resistance between terminals 6 (CANH) and 14 (CANL) of the DLC3 is below 54 Ω.
Symptom
 Trouble Area
The resistance between terminals 6 (CANH) and 14 (CANL) of the DLC3 is below 54 Ω.
  1. Short in CAN bus lines
  2. Skid control ECU
  3. Steering angle sensor
  4. Yaw rate sensor
  5. ECM
  6. Gateway ECU
  7. Seat belt control ECU
  8. Distance control ECU
  9. Power steering ECU
  10. Television camera ECU
  11. Center airbag sensor
  12. CAN LH J/C
  13. CAN RH J/C

WIRING DIAGRAM

C127767E01
C127768E01

INSPECTION PROCEDURE


1. CHECK FOR SHORT IN CAN BUS LINES (DLC3 BRANCH LINE)

  1. G031934E63
    Disconnect the DLC3 branch line connector (J94) from the CAN RH J/C A side (with earth terminal).

    NOTICE:
    1. Before disconnecting the connector, make a note of where it is connected.
    2. Reconnect the connector to its original position.

  1. C126231E01
    Measure the resistance according to the value(s) in the table below.

    Standard resistance:
    Tester Connection
    		 Condition
    		 Specified Value
    J21-6 (CANH) - J21-14 (CANL)
    		 Engine switch off
    		 1 MΩ or higher



NG
REPAIR OR REPLACE DLC3 BRANCH LINE OR CONNECTOR
OK


2. RECONNECT CONNECTOR

  1. Reconnect the DLC3 branch line connector (J94) to the CAN RH J/C A side (with earth terminal) .


NEXT


3. CHECK FOR SHORT IN CAN BUS LINES (BRANCH LINE)

  1. C126231E01
    Connect the probes of an ohmmeter to terminals 6 (CANH) and 14 (CANL) of the DLC3.

  1. While observing the resistance value shown on the tester, disconnect connectors J1, J3, J4, J5, J8, J82, J96, and J97 from the CAN LH J/C or CAN RH J/C one by one until the resistance becomes normal (between 54 and 69 Ω).

    HINT:
    Disconnect the branch line connectors other than those of the DLC3.

    C128149E01
    C128147E01
    Wiring color: 
    CAN LH J/C A Side (with Earth Terminal)
    		 Code
    		 Color (CANH Side)
    		 Color (CANL Side)
    Power steering ECU
    		 J1
    		 P
    		 W
    ECM
    		 J2
    		 B
    		 W
    Seat belt control ECU
    		 J3
    		 V
    		 W
    Center airbag sensor
    		 J4
    		 R
    		 W
    Wiring color: 
    CAN LH J/C B Side (without Earth Terminal)
    		 Code
    		 Color (CANH Side)
    		 Color (CANL Side)
    Yaw rate sensor
    		 J5
    		 P
    		 W
    CAN main bus line (bus line connecting CAN LH J/C and CAN RH J/C)
    		 J7
    		 B
    		 W
    Television camera ECU
    		 J8
    		 L
    		 W
    C128148E01
    Wiring color: 
    CAN RH J/C A Side (with Earth Terminal)
    		 Code
    		 Color (CANH Side)
    		Color (CANL Side)
    CAN main bus line (bus line connecting CAN RH J/C and CAN LH J/C)
    		 J81
    		 B
    		 W
    Steering angle sensor
    		 J82
    		 P
    		 W
    DLC3
    		 J94
    		 G
    		 W
    Skid control ECU
    		 J96
    		 R
    		 W
    Wiring color: 
    CAN RH J/C B Side (without Earth Terminal)
    		 Code
    		 Color (CANH Side)
    		Color (CANL Side)
    Gateway ECU
    		 J84
    		 B
    		 W
    Distance control ECU
    		 J97
    		 GR
    		 W

    NOTICE:
    Do not reconnect the disconnected connectors until this inspection is complete because there may be a short in 2 or more branch lines.


    Result:
    Symptom
    		 Proceed to
    The resistance is still below 54 Ω when all the specified connectors are disconnected. (There are no shorts in the branch lines.)
    		 A
    The resistance becomes normal (between 54 and 69 Ω) when a connector is disconnected. (There is a short in one or more of the branch lines.)
    		B

  1. When there is a short in one or more of the branch lines:

    1. Reconnect all of the connectors to the CAN J/C, except for the one that was disconnected last (the short-circuited bus line). Check that the resistance shown on the tester is normal (between 54 and 69 Ω) to confirm that there is a short in the one branch line only.

      HINT:
      1. The connectors connected to the CAN J/C can be distinguished according to the color of the communication bus lines and the shape of the connectors.
      2. Reconnecting the connectors to non-specified positions on the CAN J/C does not affect system operation. However, it is preferred to reconnect the connectors to their specified positions to avoid negative effects on the wiring such as tension on the wiring harnesses, and to make future maintenance easier.



 B
Go to step 9
A


4. CHECK FOR SHORT IN CAN BUS LINES (GATEWAY ECU MAIN BUS LINE)

  1. G031932E92
    Disconnect the gateway ECU main bus line connector (J84) from the CAN RH J/C B side (without earth terminal) .

    NOTICE:
    1. Before disconnecting the connector, make a note of where it is connected.
    2. Reconnect the connector to its original position.

  1. C126231E01
    Measure the resistance according to the value(s) in the table below.

    Standard resistance:
    Tester Connection
    		 Condition
    		 Specified Value
    J21-6 (CANH) - J21-14 (CANL)
    		 Engine switch off
    		 108 to 132 Ω


    Result:
    Symptom
    		 Proceed to
    The resistance is still below 54 Ω when the gateway ECU connector is disconnected. (There are no shorts in the gateway ECU main bus lines.)
    		 A
    The resistance falls within the specified range (between 108 and 132 Ω) (either of the terminating resistances is normal) when the gateway ECU connector is disconnected. (There is a short in the gateway ECU main bus lines.)
    		B



B
Go to step 11
A


5. CHECK FOR SHORT IN CAN BUS LINES (ECM MAIN BUS LINE)

  1. G031934E61
    Disconnect the ECM main bus line connector (J2) from the CAN LH J/C A side (with earth terminal) .

    NOTICE:
    1. Before disconnecting the connector, make a note of where it is connected.
    2. Reconnect the connector to its original position.

  1. C126231E01
    Measure the resistance according to the value(s) in the table below.

    Standard resistance:
    Tester Connection
    		 Condition
    		 Specified Value
    J21-6 (CANH) - J21-14 (CANL)
    		 Engine switch off
    		 1 MΩ or more

    HINT:
    Measure the resistance with the gateway ECU main bus line connector (J84) disconnected.


    Result:
    Symptom
    		 Proceed to
    The resistance is still below 1 MΩ when the ECM connector is disconnected. (There are no shorts in the ECM main bus lines.)
    		 A
    The resistance becomes 1 MΩ or more when the ECM connector is disconnected. (There is a short in the ECM main bus lines.)
    		B



B
Go to step 13
A


6. CHECK CAN RH J/C

  1. G031934E59
    Disconnect the CAN main bus line connector (J81) from the CAN RH J/C A side (with earth terminal) .

    NOTICE:
    1. Before disconnecting the connector, make a note of where it is connected.
    2. Reconnect the connector to its original position.

  1. C126231E06
    Measure the resistance according to the value(s) in the table below.

    Standard resistance:
    Tester Connection
    		 Condition
    		 Specified Value
    J21-6 (CANH) - J21-14 (CANL)
    		 Engine switch off
    		 1 MΩ or more



NG
REPLACE CAN RH J/C
OK


7. RECONNECT CONNECTOR

  1. Reconnect the CAN main bus line connector (J81) to the CAN RH J/C A side (with earth terminal).


NEXT


8. CHECK CAN LH J/C

  1. G031932E93
    Disconnect the CAN main bus line connector (J7) from the CAN LH J/C B side (without earth terminal) .

    NOTICE:
    1. Before disconnecting the connector, make a note of where it is connected.
    2. Reconnect the connector to its original position.

  1. C126231E01
    Measure the resistance according to the value(s) in the table below.

    Standard resistance:
    Tester Connection
    		 Condition
    		 Specified Value
    J21-6 (CANH) - J21-14 (CANL)
    		 Engine switch off
    		 1 MΩ or higher



OK
REPLACE CAN LH J/C
NG

REPAIR OR REPLACE CAN MAIN BUS LINE (CAN LH J/C - CAN RH J/C)

9. RECONNECT CONNECTOR

  1. Reconnect the connector for the short-circuited branch line to the CAN J/C (the connector that caused the bus line resistance to become normal (between 54 and 69 Ω) when it was disconnected).


NEXT


10. CHECK FOR SHORT IN CAN BUS LINES

  1. C126231E01
    Disconnect the connector that includes terminals CANH and CANL from the ECU (or sensor) to which the short-circuited branch line is connected. (Click here)

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

    Standard resistance:
    Tester Connection
    		 Condition
    		 Specified Value
    J21-6 (CANH) - J21-14 (CANL)
    		 Engine switch off
    		 1 MΩ or higher

    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).



 NG
REPAIR OR REPLACE CORRESPONDING ECU OR SENSOR BRANCH LINE OR CONNECTOR
OK

REPLACE CORRESPONDING ECU OR SENSOR

11. RECONNECT CONNECTOR

  1. Reconnect the gateway ECU main bus line connector (J84) to the CAN RH J/C B side (without earth terminal) .


NEXT


12. CHECK FOR SHORT IN CAN BUS LINES (GATEWAY ECU)

  1. C126231E01
    Disconnect the gateway ECU connector (J76).

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

    Standard resistance:
    Tester Connection
    		 Condition
    		 Specified Value
    J21-6 (CANH) - J21-14 (CANL)
    		 Engine switch off
    		 108 to 132 Ω

    HINT:
    If the resistance becomes normal (between 108 to 132 Ω) when the connector is disconnected, there may be a short in the gateway ECU.



 NG
REPAIR OR REPLACE CAN MAIN BUS LINE (GATEWAY ECU MAIN BUS LINE)
OK

REPLACE GATEWAY ECU

13. RECONNECT CONNECTOR

  1. Reconnect the ECM main bus line connector (J2) to the CAN LH J/C A side (with earth terminal) .


NEXT


14. CHECK FOR SHORT IN CAN BUS LINES (ECM)

  1. C126231E01
    Disconnect the ECM connector (A5).

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

    Standard resistance:
    Tester Connection
    		 Condition
    		 Specified Value
    J21-6 (CANH) - J21-14 (CANL)
    		 Engine switch off
    		 1 MΩ or higher

    HINT:
    1. Measure the resistance with the gateway ECU main bus line connector (J84) disconnected.
    2. If the resistance changes to 1 MΩ or more when the connector is disconnected, there may be a short in the ECM.



 NG
REPAIR OR REPLACE CAN MAIN BUS LINE (ECM MAIN BUS LINE)
OK

REPLACE ECM


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