U0073 Code: Control Module Communication Bus A Off
U0073 Code: Find the Network Fault Before Replacing Modules
U0073 records a bus-off network event. Save the module pattern, map the exact topology and prove the affected branch before replacing controllers.
U0073 means Control Module Communication Bus A Off. A controller detected enough communication errors for its network interface to enter a bus-off state. It does not prove the entire vehicle network failed or identify one bad module. Preserve the all-module scan, check battery voltage and module powers/grounds, map what the manufacturer calls Bus A, then inspect and test the affected connectors, wiring and branch.
What the U0073 Code Actually Tells You
Modern vehicles use several communication networks and gateways. A module sends and receives data, monitors transmission errors and can stop participating when its CAN controller reaches a bus-off condition. U0073 records that network event; a companion lost-communication code often gives the more useful clue about which module or branch disappeared.
Bus A is a manufacturer-specific topology label. It may be described as high-speed CAN, GMLAN, CAN 2 or another network name, and it is not guaranteed to use the same diagnostic-connector pins, speed or termination layout on every vehicle. The reporting module, failure suffix and complete module inventory are essential evidence.
Identify which controller stored U0073 and whether it is current or history.
Compare responsive modules, missing nodes and companion U-codes.
Use the OEM map to locate gateways, splices, terminators and branches.
Five U0073 Causes in Test Order
Start with voltage and shared module supplies. A controller should be the last conclusion because a powerless or disconnected module cannot communicate.
Battery, Charging, Power, or Ground Fault
A weak battery, voltage drop, poor cable, open fuse or lost module ground can make one or more controllers reset and stop communicating.
How to prove it: Test battery and charging condition plus loaded power and ground at the affected modules before touching network wiring.
Check firstConnector, Splice, or Twisted-Pair Damage
Water, corrosion, backed-out pins, chafing, a pinched harness, open conductor or short between bus wires can drive a CAN controller bus-off.
How to prove it: Use the VIN-specific topology to inspect the relevant connector, splice or branch instead of assuming the whole bus is damaged.
Check firstAftermarket Device or Recent Electrical Work
A remote starter, alarm, radio, telematics device, diagnostic dongle or recent repair can load, short or inject errors into the network.
How to prove it: Document recent work and follow the OEM procedure to remove unsupported inline or DLC devices for comparison.
Test directlyOne Module or Transceiver Pulling Down a Segment
An internally shorted or noisy controller can affect every node on its branch, but an offline module may also be only a victim of lost power or wiring.
How to prove it: Prove module supply and ground, then isolate branches with the specified breakout method; do not condemn the first missing module.
Test directlyGateway, Termination, Configuration, or Software Branch
A gateway, junction, termination point, incorrect replacement setup or vehicle-specific software issue remains possible after physical evidence passes.
How to prove it: Verify topology, termination design and applicable service information before programming or replacing a gateway or controller.
Final branch
Architecture warning: newer vehicles can combine several CAN buses, CAN FD, LIN, FlexRay or Ethernet behind a gateway. Heavy-duty and high-voltage platforms can use different connectors, protocols and power-down procedures.
U0073 Symptoms and Driving Safety
The symptom set depends on the lost network branch. A history code may have no current effect, while an active fault involving brake, steering, engine or transmission modules can be unsafe.
ABS, stability, steering, transmission, engine or body-system warnings can appear when affected modules stop exchanging data.
A full-system report may show that several controllers respond while one module or one network branch is absent.
If authorization, engine or transmission data are lost, the vehicle may not start, may stall or may enter a protective mode.
Gauges, warning messages, radio, HVAC, locks or other functions can behave unpredictably when their source data disappear.
Vibration, moisture, heat, harness movement or a plug-in accessory can make the network recover and fail again.
A low-voltage or temporary short event may leave U0073 stored even after communication returns. Preserve the original pattern.
Using UR1000 to Organize the Network Evidence
The iCARZONE UR1000 can perform a supported full-system scan, save DTCs and freeze frame, show which controllers respond, display available ECU information and live data, and create a diagnostic report. Comparing current and history U-codes across modules helps identify whether the event is local to one branch or follows a shared voltage or gateway problem.
Coverage varies by VIN, module and secure-gateway access. A scan tool cannot communicate with a node while that node or its branch is offline. UR1000 does not physically measure CAN-H/CAN-L voltage, network resistance, waveform, terminal tension, harness continuity or a transceiver fault. Those checks require OEM diagrams plus a suitable multimeter, scope and breakout equipment.
iCARZONE UR1000 Bidirectional Scan Tool with ECU Coding
Save the U0073 module pattern, compare companion codes and document verification. Confirm exact vehicle and gateway coverage before purchase.
How to Diagnose U0073 in 6 Steps
Do not begin by clearing codes or randomly unplugging controllers. SRS, brake, steering and high-voltage modules require the specified shutdown sequence, and measuring resistance on an energized bus can damage equipment or create misleading results.
Compact U0073 Test Path
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1
Save the Complete Network Event
- Do not clear codes first. Save every module report, U0073 status, failure suffix, freeze frame and the identity of each module that stored a fault.
- Record which controllers respond, which are absent and which specific lost-communication or invalid-data codes accompany U0073.
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2
Check Safety, Battery, Powers, and Grounds
- Confirm whether brake, steering, restraint, engine or transmission functions are affected before deciding whether the vehicle can move safely.
- Test battery and charging condition plus loaded feeds, fuses and grounds shared by the missing modules or gateway.
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3
Map What This Vehicle Calls Bus A
- Use the VIN-specific network diagram to identify the bus name, gateway, splice packs, termination points and branch layout.
- Do not assume Bus A is always high-speed CAN or always available at the same diagnostic-connector pins.
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4
Inspect Recent Work, Devices, and Connections
- Review jump-start, battery, collision, water, module and accessory history. Remove unsupported inline devices only by the approved procedure.
- After the required shutdown, inspect accessible connectors, seals, terminal fit and twisted-pair routing without spreading pins.
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5
Test and Isolate the Physical Network
- Let modules enter the specified sleep state before resistance testing; never measure resistance on an energized network.
- Use OEM resistance, bias-voltage and scope procedures, then isolate branches one at a time with suitable breakout tools.
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6
Repair the Proven Branch and Verify
- Repair the failed power, ground, terminal, splice, wiring, accessory or module branch; program a controller only when required.
- Clear codes after evidence is saved, recreate the trigger, road-test safely and confirm a complete module inventory with no recurring faults.
U0073 Repairs and Cost Factors
Voltage, Power, or Ground
Correct the battery, cable, charging, fuse, relay, feed or ground fault proven under load.
Connector or Network Wiring
Restore terminals, seals, splices and twisted-pair routing with the specified repair method.
Accessory or Failed Branch
Remove the proven interfering device or repair the isolated branch that pulls down the segment.
Gateway or Module
Replace, configure or program a controller only after its supply, ground and network are proven.
These broad planning ranges are not quotes. Intermittent reproduction, topology access, water damage, harness length, secure-gateway work, programming and local labor can change the total.
Scan and Network Diagnosis
$150–$450Complete module inventory, diagrams and fault reproduction.
Battery, Connection, or Ground
$100–$700Battery type, cable access and loaded circuit repair.
Connector or Harness Branch
$150–$3,000+Local terminal repair versus major harness access or replacement.
Gateway or Module
$500–$2,500+Final module proof, coding, security setup and verification.
DIY Limits and Vehicle Differences
A useful DIY contribution is preserving the scan pattern and checking obvious, accessible power problems. Physical network diagnosis becomes professional work when branch isolation, safety modules or secure programming are involved.
- Save the full scan before clearing codes.
- Inspect battery terminals and diagram-listed fuses.
- Document recent accessories, water or repair work.
- Inspect accessible connectors after proper shutdown.
- Scope, resistance and network-bias testing.
- Branch isolation and gateway diagnosis.
- SRS, ABS, steering or high-voltage modules.
- Controller setup, coding and programming.
Frequently Asked Questions About U0073
What does U0073 mean?
Does U0073 mean the ECM or gateway is bad?
Can UR1000 diagnose U0073?
Can I drive with U0073?
Is 60 ohms always the correct CAN-bus reading?
Sources and Technical Review Notes
- BMW SAE P-code list — confirms U0073 as Control Module Communication Bus A Off.
- Subaru electrical training material hosted by NHTSA — explains CAN line faults, lost-module patterns and why a branch open can require topology-based isolation.