U0073
Control Module Communication Bus "A" Off
A control module has detected that the communication bus is non-functional and has shut its bus interface off. Affects multiple modules at once because none can communicate; on most vehicles the dashboard lights up with several warning lamps simultaneously.
- Check engine light: Yes
- Emissions related: No
- Repair difficulty: hard
Symptoms
- Multiple warning lights may illuminate
- Affected modules may go into limp mode or shut down
- Specific functions inoperative depending on module
- Diagnostic tools may show communication faults
Common causes
Ordered by how often each turns out to be the cause.
- CAN line shorted to supply or groundCommon
- Terminating resistor failedPossible
- One failing module pulling the bus downPossible
Parts involved
- CAN Bus Wiring
- CAN Terminating Resistor
- Control Module
U0073 is a generic OBD-II code defined by SAE J2012. Exact wording and diagnostic procedure vary by manufacturer and model. Code definitions are drawn from the public-domain OBDex dataset; the workshop notes are our own.