U0073 – Control Module Communication Bus Off

U0073 means the vehicle’s modules stopped talking on a shared communication network, and the car may act “possessed” with multiple warnings or no-start conditions. You may lose gauges, ABS, power steering assist, or shifting quality because key modules cannot exchange data. The official definition is “Control Module Communication Bus Off.” According to factory diagnostic data used across many brands, this U0073 code sets when a controller decides the network is unusable and takes itself off the bus to protect communication. The code does not prove a bad module. It points you toward a network, power/ground, or wiring fault that you must confirm.

U0073 Quick Answer

U0073 points to a network “bus off” event, not a single failed part. Check which module dropped off the scan tool first, then verify network wiring and module power/grounds under load.

What Does U0073 Mean?

U0073 means a control module detected a communication bus-off condition on the vehicle network. In plain terms, the car’s computers share a data “party line,” and one or more modules can no longer communicate reliably. When that happens, other systems that depend on shared data may stop working or go into fail-safe. The official definition stays intentionally general under SAE J2012. That vagueness is by design, so you must identify which module and which network segment caused the bus-off event.

Technically, “bus off” describes a controller state where the module stops transmitting on the network after repeated communication errors. The module does not measure a single sensor value here. It monitors network integrity, message timing, and error handling on the communication bus. Diagnosis matters because a shorted CAN/LIN wire, poor splice, weak module power/ground, or a single module loading the network can all trigger U0073 without that module being “bad.”

Theory of Operation

Modern vehicles use a communication network so modules can share inputs and commands. The ECM/PCM, TCM, ABS module, body control module, power steering, and HVAC exchange data continuously. Each module sends messages and also “listens” for others. When the network stays healthy, the scan tool can see every installed module, and live data updates smoothly.

U0073 sets when a module detects excessive network errors and protects the bus by stopping communication. Wiring faults can corrupt signals and create errors. Poor grounds and low system voltage can also distort network waveforms. A single module with an internal fault can load the network and prevent clean communication. Because U-codes are reuseable across platforms, you must confirm the affected bus and the missing module list on your specific vehicle before you plan a repair.

Symptoms

U0073 symptoms usually show up as multiple systems acting up at once, especially during cranking or when hitting bumps.

• Scan tool: one or more modules show “no communication,” disappear from the module list, or drop out during a network scan
• Warning lights: multiple lamps illuminate together (ABS, traction control, power steering, airbag, or MIL depending on the module that went offline)
• No-start or stall: the engine may crank with no start, stall at idle, or restart only after a key cycle
• Gauge operation: cluster resets, gauges sweep, or the odometer/info screen flickers or goes blank
• Transmission behavior: harsh shifts, limp mode, or a PRNDL display that does not match shifter position
• Steering/brake assist: intermittent loss of electric power steering assist or ABS/ESC functions due to missing network data
• Intermittent nature: symptoms worsen with vibration, rain, aftermarket accessories, or low battery voltage

Common Causes

• CAN bus short to ground: A chafed CAN-H or CAN-L wire can pull the bus low and force modules into a bus-off state.
• CAN bus short to power: A short to B+ drives the bus high and corrupts messages until the network shuts down communication.
• High resistance at a splice or junction: Corrosion or a loose splice adds resistance and distorts the CAN waveform, triggering repeated errors and bus-off.
• Open circuit in CAN-H or CAN-L: A broken conductor or backed-out terminal prevents proper differential signaling and stops reliable module messaging.
• Module power or ground fault: A weak feed or high-resistance ground makes a module reset or “drop off” the network, which can cascade into bus errors.
• Water intrusion in a network connector: Moisture bridges terminals and creates intermittent shorts that spike error counts and set U0073.
• Aftermarket device interfering with the network: Remote starts, alarms, trackers, and audio interfaces can load the bus or miswire CAN, causing bus-off events.
• Faulty control module transceiver (rare): An internal CAN driver fault in any module can dominate the bus and prevent normal communication.

Diagnosis Steps

Use a scan tool that can run a full network scan and show pending vs confirmed DTCs. You also need wiring diagrams, a quality DVOM, and back-probing tools. A labscope helps confirm bus integrity fast, but you can still prove most faults with voltage-drop tests and careful connector inspection.

1. Confirm U0073 and record freeze-frame data for each module that stored it. Focus on ignition state, vehicle speed, system voltage, and any other U-codes or low-voltage codes that set at the same time.
2. Run a full network scan and document which modules do not respond. Then check whether U0073 shows as pending or confirmed, since some platforms require two trips before confirmation and others will reset immediately with a hard fault.
3. Check fuses, relays, and power distribution that feed the non-responding modules and network gateways. Do not start probing CAN wiring until you verify clean system voltage and proper module wake-up power.
4. Verify module power and ground under load with voltage-drop testing. Measure from battery positive to the module B+ pin with the circuit operating, then measure from the module ground pin to battery negative; keep ground drop under 0.1V with the module awake.
5. Perform a targeted visual inspection of the CAN harness routing and connector areas. Look for rub-through near brackets, pinched sections at the radiator support, and damage near the battery, under- modules, and kick panels.
6. Disconnect and inspect network connectors for spread terminals, corrosion, or water tracks. Pay close attention to splice packs, gateway connectors, and any connector that shares multiple modules on one bus segment.
7. Check for aftermarket equipment tied into CAN wiring or power feeds. Isolate it by unplugging the device harness, then repeat the network scan to see if modules return.
8. Measure CAN line bias voltages with ignition ON, engine OFF. Communication bias only exists when the network powers up, so ignition-OFF readings do not help; compare CAN-H and CAN-L for reasonable, stable bias and watch for a line stuck high or low.
9. Perform circuit integrity checks only after you isolate the suspected segment. Use continuity and short-to-power/ground tests between CAN-H/CAN-L and power/ground with modules disconnected as needed, and verify you did not backfeed the circuit during testing.
10. Use a scan tool snapshot during a road test if the fault acts intermittent. Freeze frame shows the conditions when U0073 set, while a snapshot captures the moment the bus drops out during your drive and helps you link it to bumps, load, or voltage changes.
11. Confirm the repair by clearing codes and repeating a full network scan. Verify all modules report, U0073 does not return as pending, and the original symptom stays gone after a complete key cycle and test drive.

Professional tip: When U0073 sets with multiple low-voltage or ignition feed codes, fix the power/ground problem first. A clean-looking ground can still fail under load, so trust voltage-drop numbers, not continuity checks.

Possible Fixes

• Repair chafed CAN wiring and restore proper routing and protection where the harness rubs or pinches.
• Clean, dry, and reseat network connectors, then repair any corroded terminals or compromised seals.
• Restore module power and ground integrity by repairing fuse box faults, loose grounds, or high-resistance splices found by voltage-drop testing.
• Remove or correctly rewire aftermarket devices that load or miswire the CAN network, then verify normal module communication.
• Repair an open or high-resistance CAN segment by correcting splice pack issues or replacing damaged connector housings.
• Reprogram or replace a control module only after you prove it disrupts the bus and all wiring and power/ground checks pass.

Can I Still Drive With U0073?

You can sometimes drive with a U0073 code, but you should treat it as a reliability risk. U0073 means a module reported the communication bus went “bus off,” so messages stopped flowing on that network. The vehicle may run normally one moment, then lose functions the next. Expect warning lights, inoperative gauges, no-start, or a stall if a critical module drops out. If the engine runs rough, the transmission shifts harshly, or the scan tool cannot communicate with multiple modules, stop driving and tow it. Also avoid driving if you lose ABS, stability control, electric steering assist, or brake assist warnings. Those systems can rely on network data.

How Serious Is This Code?

U0073 ranges from an inconvenience to a safety problem, depending on which network and modules drop offline. When the fault hits a non-critical bus segment, you may only lose infotainment, HVAC control, or a few warning indicators. When it hits the main high-speed network, the vehicle can lose ABS, traction control, power steering assist, transmission coordination, and even immobilizer authorization. Intermittent “bus off” events also create secondary DTCs that mislead diagnosis. Treat any U0073 with multiple drivability complaints as high severity. If the vehicle logs U0073 as confirmed and repeats after a key cycle, you need a network integrity diagnosis before regular use.

Common Misdiagnoses

Technicians often replace a module because it “won’t talk,” then the new module still cannot communicate. A U0073 code does not prove a module failed; it proves the bus went offline. Another common mistake involves chasing dozens of U-codes without identifying the first failure. One shorted module or a rubbed-through CAN wire can cascade into many “lost communication” codes. Many people also skip power and ground voltage-drop tests under load. A module with a weak ground can reset and take the bus down. Avoid guessing by doing a full network scan, identifying which modules disappear, and then isolating the branch or connector that triggers the bus-off event.

Most Likely Fix

The most common confirmed U0073 repair paths involve wiring and power integrity, not immediate module replacement. Start with the basics that repeatedly cause “bus off”: repair a shorted or chafed network harness, correct spread or corroded terminals at a backbone connector, or restore a weak module power or ground that causes resets. If the fault appears when you move the harness, focus on that area and load-test the circuits. If unplugging one suspect module restores network communication, treat that as a strong lead. Confirm it with wiring checks and verify the module’s power, ground, and connector condition before condemning it.

Repair Costs

Network and communication fault repairs vary by root cause — wiring/connectors are often the source, but module-level repairs or replacements can be significantly more expensive.

Last updated: March 31, 2026