FixItFor.Us
U codenetworkMedium severity

U0075Control Module Communication Bus "C" Off

A control module has stopped transmitting on communication bus "C" after detecting excessive errors, a condition known as bus-off.

Definition

Each CAN controller counts transmit and receive errors; when the transmit error counter passes its threshold, the controller enters a bus-off state and disconnects from the network to protect it, setting U0075 for bus "C". Which systems ride on bus "C" varies by manufacturer (often a chassis or secondary network), so symptoms range from inoperative accessories to disabled chassis functions and multiple warning lights. Communication may recover intermittently as the controller resets, making the fault appear sporadic.

Common causes

  • Intermittent short or open in the bus "C" wiring driving the error counter up
  • Corroded or loose connector terminals on the bus
  • A failing module on bus "C" transmitting corrupted frames
  • Low battery voltage or poor module grounds
  • Electrical noise from damaged shielding or a failing alternator
  • Aftermarket devices connected to the bus

Common misdiagnoses

  • The module that logged U0075 replaced, when it is only the reporter of a bus problem
  • Multiple modules replaced chasing lost-communication codes
  • Battery replaced for what is a wiring fault
  • Gateway module replaced without circuit testing

Troubleshooting steps

  1. 1.Identify which network is bus "C" on this vehicle

    Consult the manufacturer's network topology diagram — bus letters are OEM-specific, and the diagram lists every module on that bus.

  2. 2.Scan all modules and note where U0075 is stored

    If several modules on the bus store it, the fault is in shared wiring; if only one does, suspect that module's own connection or transceiver.

  3. 3.Test the bus circuits

    Check the pair for shorts to ground, shorts to power, shorts together, and correct termination resistance per the service manual values.

  4. 4.Verify supply voltage and grounds

    Confirm charging voltage of 13.5-14.7 V running and clean, tight grounds for the modules on the bus.

  5. 5.Isolate a corrupting module

    Disconnect bus "C" modules one at a time and watch whether the remaining network stops logging errors.

  6. 6.Wiggle-test for the intermittent

    Bus-off faults are frequently intermittent; flex harness sections while monitoring communication to expose the defect.

Related codes