U0073 code: Control Module Communication Bus A Off
U0073 means control Module Communication Bus A Off. The code says where to look, not what failed — the fix depends on which cause your car actually has.
What U0073 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.
U0073 symptoms
- 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 U0073
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 →How to fix U0073
Advanced — usually a shop job unless you’re well equipped
- Rule out a voltage-triggered bus-off event
Charge the battery, load-test it, and confirm running voltage is normal. A bus-off logged once during a jump start, battery swap, or weak crank can be a stored leftover rather than an active fault — clear it, drive, and see whether it returns before tearing into the harness.
- Map which modules answer and which go silent
Run a network or topology scan and note every module that responds. U0073 usually travels with a group of lost-communication codes; if the missing modules share one branch of the wiring diagram, the fault likely sits on that branch, while a scan tool that can't reach anything through the diagnostic port suggests the whole bus is shorted or held down.
- Measure the bus at the diagnostic connector
With the battery disconnected, many CAN networks read roughly 60 ohms between CAN high and CAN low (pins 6 and 14 on the 16-pin connector) with both terminating resistors present; around 120 ohms suggests one end is open, and near zero means the lines are shorted together. Key on, a line pinned at 0 volts or battery voltage is shorted. Confirm expected values per the service manual.
- Check splice points, water paths, and add-on wiring
Bus wires often meet at junction connectors or splice packs under the dash, in the kick panels, or near the fuse boxes — spots that see water from leaking cowls, sunroof drains, or door seals. Look for corrosion there, and unplug aftermarket remote starters, trackers, or radio interfaces tapped into the network, since a bad add-on can pull the whole bus down.
- Isolate modules one at a time
If the bus still reads wrong, unplug modules one by one, guided by the diagram, while watching resistance or the scan tool. When the bus recovers, the last module or its branch wiring is the culprit. A replacement module usually needs programming to the vehicle before the network is whole again.
DIY or shop? A home mechanic can handle the battery work, a scan to see which modules drop out, and a careful look for water and corrosion around junction connectors — and a multimeter at the diagnostic port gives a useful first read on the bus. Past that, U0073 is a wiring-diagram job: isolating a shorted segment means locating splice packs behind trim, back-probing module connectors, and sometimes using an oscilloscope to see a corrupted signal. Any module replaced along the way typically needs programming, which puts the finish in a shop's hands.
Tools for the DIY steps: Full-system scan tool · Digital multimeter · Battery charger or load tester · Wiring diagram for the vehicle · Back-probe pins
Not sure which step applies to your car? Get the likely cause for your exact vehicle before buying anything for U0073.
Start a case with U0073 and your car. Redline weighs these causes against what your car shows, and names the check that would settle it before you buy parts.
Can I drive with U0073?
Redline can’t determine from a symptom or code alone whether your car is safe to drive.
U0073: common questions
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?
It can. 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.
Related trouble codes
Don’t have a scanner yet? A ~$25 Bluetooth adapter reads codes like U0073 from your phone. See our guide to the best OBD2 Bluetooth adapters. Run a repair shop? See Redline for shops.
Generic OBD-II reference. Manufacturer-specific behavior varies. Confirm with a scan tool and, for safety-related codes, a professional inspection. Cost ranges are reference ranges, not quotes.
Seeing U0073 on your car?
Every problem becomes a Case. Tell Redline what the car is doing: it shows what the evidence supports, what’s still missing, and what to check next, before you approve a repair.
“Inner pad ~1 mm. Outer pad 3 mm.”
Next: check the slide pins move freely before buying parts.