Network communication (U-codes) · Network · generic (SAE-defined)
U0073: Control Module Communication Bus "A" Off
U0073 means a control module detected that the primary vehicle communication network, bus A, has gone silent or shut down, so modules cannot exchange data.
Standard title per SAE J2012 / ISO 15031-6 · Updated 2026-11-07 · By CarWhere Research
How U0073 sets
Vehicle modules share information over a controller area network (CAN). When a module sees the bus stop carrying valid messages, or detects that its own bus connection has shut down because of errors, it stores U0073. The setting conditions and which bus is called A vary by manufacturer.
Common causes of U0073
Roughly most likely first; the actual cause depends on the vehicle and needs testing to confirm.
- Short or open in the CAN bus wiring
- Failed module pulling the network down
- Corroded or water-damaged connectors
- Low battery voltage or poor grounds
- Damaged terminating resistor
- Aftermarket accessories spliced into the network
U0073 symptoms
- Check engine light and multiple warning lights on
- Gauges dropping out or behaving erratically
- No-start or stalling
- Transmission in a default gear
- Multiple U codes stored in several modules
How U0073 is diagnosed
- Scan all modules and record which ones report communication codes.
- Check battery voltage, charging voltage, and main grounds.
- Measure CAN bus resistance at the diagnostic connector with the battery disconnected, comparing to factory specification.
- Check CAN high and low voltages for shorts to ground or power.
- Disconnect modules one at a time to see if the network recovers.
- Inspect connectors and harnesses in water-prone or chafe-prone areas.
Typical fixes for U0073
- Repair shorted or open CAN wiring
- Clean or repair corroded connectors
- Replace a module that is disrupting the bus
- Repair battery, charging, or ground faults
- Remove improperly installed aftermarket devices
Replace parts only after testing confirms the cause — a code names the circuit or condition that failed a check, not necessarily the faulty part. We don’t publish per-repair prices; for what households actually spend on upkeep, see car repair costs.
Related codes & warning lights
U0073 FAQ
What does code U0073 mean?
U0073 means a control module detected that the primary vehicle communication network, bus A, has gone silent or shut down, so modules cannot exchange data. The standard definition is "Control Module Communication Bus "A" Off."
Can I drive with a U0073 code?
Not recommended until it is diagnosed. With the network down, the transmission, braking aids, gauges, and other systems may not work correctly, and the vehicle may not start or may stall.
Can a weak battery cause U0073?
Yes. Low or unstable voltage can make modules drop off the network and set communication codes, so battery testing is an early step.
Why do so many warning lights come on with U0073?
Modules depend on shared network data, so when the bus goes down, many systems lose information they need and set their own warnings.
Keep researching
More network communication (u-codes) codes
Sources
- SAE J2012 — Diagnostic Trouble Code Definitions (standard code titles)
- ISO 15031-6 — Road vehicles: communication between vehicle and external equipment for emissions-related diagnostics, Part 6: Diagnostic trouble code definitions
- U.S. EPA — Vehicle Emissions Inspection and Maintenance (I/M) programs
- U.S. EPA, 40 CFR 86.1806-17 — Federal onboard diagnostics requirements for light-duty vehicles
General information written by CarWhere Research, not a diagnosis of your vehicle. Manufacturers can add their own sub-definitions and test conditions; confirm with the factory service information for your year, make and model. Before paying for a repair, check NHTSA for open recalls and your warranty booklet: federal law requires an emissions warranty on major emission-control parts such as the catalytic converter and engine computer.