OBD codes / U0073
U0073
SeriousControl Module Communication Bus A Off
When the communication bus goes down, multiple systems can misbehave at once — gauges, transmission behavior, stability control, even starting. Don't treat a car doing this as reliable transportation. If the fault is intermittent, drive gently and locally at most, and get it diagnosed promptly.
What this code means
U0073 means the main data network the car's computers use to talk to each other — the CAN bus — went silent or unusable, and a module recorded that the bus was 'off.' Unlike lost-communication codes that name a specific module, this one says the shared network itself failed, which is why it often appears with a cluster of other U-codes and multiple warning lights at once. Common causes are a short or open in the bus wiring (two wires that run between many modules), a corroded connector, water intrusion, a failing module pulling the whole network down, or poor power and grounds. Low battery voltage can also cause phantom network codes, so verifying battery and charging voltage is the mandatory first step. This is a diagnosis-heavy code — finding which segment or module killed the bus is the work.
Symptoms you might notice
- Multiple warning lights on at once
- Several other U-codes stored across modules
- Gauges dead or erratic
- No-start or stalling
- Scan tool unable to reach some modules
What it costs to fix
Varies by vehicle — get it diagnosed.
The repair cost for this code depends too much on your exact vehicle and the underlying cause to quote a meaningful range. Confirm the cause first so you only pay for the fix you actually need.
Diagnose U0073 for my vehicle →Frequently asked
Can I drive with U0073?
Not with confidence. A bus-off event can take out several systems simultaneously and can cause stalling or a no-start. If symptoms are active, have the car looked at before relying on it.
Why do I have so many codes along with U0073?
The CAN bus is a shared network — when it goes down, every module loses contact with every other module, and many of them store their own lost-communication codes. That flood of codes describes one network failure, not dozens of separate problems.
What should be checked first for U0073?
Battery voltage, charging output, and grounds. Low or unstable voltage is a classic cause of phantom communication codes, and it's free to check. After that, the bus wiring and connectors get inspected and modules isolated one by one.
Can one bad module take down the whole network?
Yes. Because every module shares the same two bus wires, a single failed module (or a short in its branch of the harness) can silence the entire network. Part of the diagnosis is disconnecting modules until the bus recovers.
Seeing U0073 on your car? Get a diagnosis specific to your exact year, make and model.
Diagnose U0073 for my vehicleRelated trouble codes
Don’t have a scanner yet? A ~$25 Bluetooth adapter reads codes like U0073 from your phone — see our honest guide to the best OBD2 Bluetooth adapters.
Generic OBD-II reference. Manufacturer-specific behavior varies — confirm with a scan tool and, for safety-related codes, a professional inspection.