What it means
A control module has detected that communication bus A is off. The code does not specify which module or the underlying cause.
At a glance
- Usually lights the warning light of the system that lost communication
- The engine or gearbox may go into limp mode
How it works
Communication bus A carries data among the control modules connected to that network. U0073 is set when a module detects that Bus A has stopped communicating, but the code alone does not identify the failed wire, termination, gateway path, or module.
Common causes
Most likely first.
- CAN line shorted to supply or ground
- Terminating resistor failed
- One failing module pulling the bus down
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
How to diagnose it
- Scan every reachable module and save freeze-frame and network codes to map which devices on Bus A are not responding.
- Check battery and charging voltage, then inspect accessible Bus A wiring, connectors, and splices for shorts to power or ground and physical damage.
- Use the wiring diagram to test Bus A conductors for continuity and shorts with power isolated as specified by the manufacturer.
- Measure bus termination resistance at the manufacturer-specified test points and compare it with the manufacturer's specification.
- If the wiring and termination are sound, isolate Bus A modules one at a time and check gateway routing according to the manufacturer's diagnostic procedure.
Common fixes
- Repair a Bus A wire shorted to power or ground.
- Restore a loose, corroded, or damaged Bus A connector or splice.
- Repair or replace the failed terminating component identified by measurement.
- Repair or replace the module or gateway that testing shows is taking Bus A offline.
Can I keep driving?
Do not continue driving if Bus A loss disables essential controls or the vehicle enters limp mode; otherwise, limit driving until the affected systems are identified. Multiple warning lights or unavailable functions can follow as more modules lose messages.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.