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DTC codes / U00xx · Network wiring and bus faults / U0073

U0073CAN Bus A Communication Bus Off

U0073 means the controller area network (CAN) bus that connects the vehicle's computers has gone into a bus-off state, which happens when a module detects too many transmission errors and removes itself from the network. The computer is reporting that it can no longer reliably communicate on CAN Bus A, so other modules may stop sharing data and multiple systems can act up at once.

SystemNetwork
Code typeGeneric (all makes)
SeverityMedium
Fix difficultyProfessional
AreaNetwork wiring and bus faults

Symptoms you may notice

  • Multiple warning lights on the dashboard at the same time, often including the check engine light, ABS, traction control, and airbag lamps
  • The engine may start and run, but the transmission can shift harshly or stay in a limp-home gear because it is not receiving data
  • The instrument cluster may show dashes or blanks where speed, temperature, or gear position should be displayed
  • Intermittent no-start or stalling conditions when communication between the engine control module and other modules drops out
  • Often no symptoms besides the warning light, especially if the bus-off event was brief and communications recovered
  • Non-critical features such as power windows, radio, or climate control may behave erratically if they share the affected bus

Common causes, most likely first

  1. Damaged or chafed CAN wiring, especially at flex points like door jambs, trunk hinges, and near the steering column
  2. A failed or intermittently failing control module that is pulling the bus voltage out of spec or transmitting corrupt frames
  3. Loose, corroded, or backed-out pins in a CAN connector, particularly at modules exposed to moisture or vibration
  4. A short to ground or short to power on one of the two CAN bus wires, often caused by pinched harnesses during previous repairs
  5. Missing or high-resistance termination resistors inside one of the modules at the ends of the bus, which corrupt signal integrity
  6. Low battery voltage or a failing charging system that causes modules to drop offline and log bus-off faults
  7. Aftermarket electronics improperly tapped into the CAN wiring, such as alarms, telematics units, or dash cameras

How to diagnose and fix it

  1. Scan all modules for communication codes and record which modules are online and which are missing from the network
  2. Check battery voltage and charging system output, then clear codes and verify whether U0073 returns immediately or only after a drive
  3. Inspect the CAN wiring and connectors at the most accessible modules for chafing, corrosion, and loose pins, focusing on flex points
  4. Measure CAN high and CAN low voltage at the data link connector with the key on and compare against the expected values for that network
  5. Measure resistance between CAN high and CAN low with the battery disconnected to check for a short or missing termination
  6. Disconnect modules one at a time to isolate which one is pulling the bus down, then repair or replace the faulty module or harness section
  7. After repair, clear all codes, perform a full network scan, and road test to confirm no modules drop offline

What a bus-off code really tells you

  • U0073 is a network communication code, not a component failure code, so replacing the module named in a companion code without checking the wiring first is a common and expensive misdiagnosis.
  • A single failed module can take down the entire bus and set U0073 in many other modules, so the module that reports the code is often not the one causing the problem.
  • Intermittent bus-off faults frequently trace to a chafed wire at a door hinge or trunk hinge that only shorts when the body flexes, which is why a static wiggle test may pass.
  • Low battery voltage during cranking or a weak alternator can cause modules to reset and log U0073 even though the CAN wiring is perfectly healthy.
  • Aftermarket accessories tapped into the CAN wires are a frequent cause on older vehicles, and disconnecting them is a cheap first step before any harness repair.

Can I keep driving with U0073?

If the vehicle runs and drives normally with only the warning light on, a short trip to a repair shop is acceptable, but avoid long highway drives because communication loss can disable safety systems without warning. If the engine stalls, the transmission stays in limp mode, or multiple safety lights are on, stop driving and have the vehicle towed.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

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