CAN COMMUNICATION SYSTEM, Diagnostic DTC:U0129

DTC Code DTC Name
U0129 Lost Communication with Brake System Control Module

DESCRIPTION

DTC No. DTC Detection Condition Trouble Area
U0129 No communication from the skid control ECU continues.

  • Skid control ECU branch line or connector

  • Power source circuit of skid control ECU

  • Skid control ECU (Brake booster with master cylinder assembly)

Tech Tips

This diagnosis procedure is for when DTC U0129 is output by the power management control ECU (GTS display: PM2 Gateway).

WIRING DIAGRAM

B001M6SE08

CAUTION / NOTICE / HINT

Note


  • Turn the power switch off before measuring the resistances between CAN main bus lines and between CAN branch lines.

  • Turn the power switch off before inspecting CAN bus lines for a ground short.

  • After the power switch is turned off, check that the key reminder warning system and light reminder warning system are not operating.

  • Before measuring the resistance, leave the vehicle as is for at least 1 minute and do not operate the power switch, any other switches or the doors. If any doors need to be opened in order to check connectors, open the doors and leave them open.

Tech Tips


  • Operating the power 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. RECONFIRM DTC OUTPUT


    1. Reconfirm DTCs.

      Tech Tips

      If DTC U1002 is output from PM2 Gateway of the power management control ECU, this indicates a sub bus 12 malfunction. Troubleshoot for DTC U1002 and check for malfunctions in the sub bus 12.

      Result
      Result Proceed to
      U1002 is not output from power management control ECU (GTS display/PM2 Gateway) A
      U1002 is output from power management control ECU (GTS display/PM2 Gateway) B

    B

    GO TO DIAGNOSIS PROCEDURE INDICATED BY OUTPUT DTC Click here

    A

  2. CHECK DTC (BRAKE SYSTEM)


    1. Connect the GTS to the DLC3.

    2. Turn the power switch on (IG).

    3. Turn the GTS on.

    4. Enter the following menus: Chassis / ABS/VSC/TRC / DTC.

      OK
      DTC C1241 is not output.

    NG

    GO TO DIAGNOSIS PROCEDURE INDICATED BY OUTPUT DTC Click here

    OK

  3. CHECK FOR OPEN IN CAN BUS LINES (SKID CONTROL ECU BRANCH LINE)


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

    2. B001LV1E03
      Text in Illustration
      *a

      Front view of wire harness connector

      (to Skid Control ECU (Brake Booster with Master Cylinder Assembly))

      Disconnect the A61 skid control ECU (brake booster with master cylinder assembly) connector.

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

      Standard Resistance
      Tester Connection Condition Specified Condition
      A61-35 (CA2H) - A61-34 (CA2L) Cable disconnected from negative (-) auxiliary battery terminal 54 to 69 Ω

    NG

    REPAIR OR REPLACE CAN BRANCH LINE OR CONNECTOR (SKID CONTROL ECU)

    OK

  4. CHECK HARNESS AND CONNECTOR (GROUND TERMINAL)


    1. B001L7UC03
      *a

      Front view of wire harness connector

      (to Skid Control ECU (Brake Booster with Master Cylinder Assembly))

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

      Standard Resistance
      Tester Connection Condition Specified Condition
      A61-28 (GND) - Body ground Cable disconnected from negative (-) auxiliary battery terminal Below 1 Ω

    NG

    REPAIR OR REPLACE HARNESS OR CONNECTOR (GROUND TERMINAL)

    OK

  5. CHECK HARNESS AND CONNECTOR (POWER SOURCE TERMINAL)


    1. Reconnect the cable to the negative (-) auxiliary battery terminal.

    2. B001L7UC02
      *a

      Front view of wire harness connector

      (to Skid Control ECU (Brake Booster with Master Cylinder Assembly))

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

      Standard Voltage
      Tester Connection Condition Specified Condition
      A61-16 (IG1) - Body ground Power switch on (IG) 11 to 14 V
      Result
      Result Proceed to
      OK (for LHD) A
      OK (for RHD) B
      NG C

    A

    REPLACE BRAKE BOOSTER WITH MASTER CYLINDER ASSEMBLY (SKID CONTROL ECU) Click here

    B

    REPLACE BRAKE BOOSTER WITH MASTER CYLINDER ASSEMBLY (SKID CONTROL ECU) Click here

    C

    REPAIR OR REPLACE HARNESS OR CONNECTOR (POWER SOURCE CIRCUIT)