U0073 means Control Module Communication Bus A Off. The main network bus that modules use to talk to each other has gone silent or is faulted, so modules cannot communicate. It is a generic OBD-II code, so the definition is the same on any make, but the most likely cause varies by engine; confirm with a scan tool and the service information for your vehicle before buying parts.
What U0073 means
Modern vehicles have many control modules that share information over a network, usually called the CAN bus. Codes starting with U mean a module has stopped hearing another one, and voltage and processor codes mean a module is not getting clean power or has an internal fault. Low battery voltage, poor grounds, blown fuses and damaged wiring cause many of these codes, so test the battery and charging system first.
U0073 symptoms
- Several warning lights at once
- Dead gauges
- No-start on some vehicles
- Transmission in limp mode
Common causes of U0073
- Shorted or open network wiring
- A failed module pulling the network down
- Water intrusion in connectors
- Low battery voltage
How to diagnose U0073
- Check battery voltage first
- Measure network resistance at the diagnostic connector (many networks read about 60 ohms between the two network pins)
- Unplug modules one at a time to find one that is pulling the network down
- Inspect wiring in areas prone to water or chafing
Can you drive with U0073?
Often not; diagnose before relying on the vehicle.
U0073 tips
A single shorted module can take down the whole network. Watching network resistance while unplugging modules one at a time is the standard way to find which module or harness branch is at fault.
Will U0073 clear itself?
If the fault stops, the computer turns off the check engine light by itself after several drive cycles without seeing it again, and the code stays in memory as history for a while. Clearing U0073 with a scan tool after a repair is fine, but if the cause is still there the code returns, sometimes within one drive. Disconnecting the battery also clears codes on most vehicles, but it erases learned fuel trims and idle settings as well.
Related codes
| Code | Meaning |
|---|---|
| U0100 | Lost Communication With ECM/PCM A |
| U0101 | Lost Communication With TCM |
| P0606 | Control Module Processor |
Guides that help
When it is more than a sensor
Voltage and network codes come from wiring, the battery, the charging system or a module, not from engine or transmission wear. If a lost-communication code has left the transmission in limp mode, rule out the module and wiring before deciding the unit has failed, and see our transmissions only if testing confirms internal damage.
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