U0073 — Control Module Communication Bus “A” Off #

Note: The exact wording of this code may vary depending on the vehicle manufacturer (OEM).

• “Control Module – Communication Bus Off” (General, SAE)
• “CAN Bus Off” (General Motors)
• “Communication Bus A Off” (Ford, Toyota, Honda)
• “CAN Network Disconnected” (Hyundai/Kia)
• “Data Bus Off State” (Volkswagen/Audi)

Summary of code U0073 #

Diagnostic Trouble Code (DTC) U0073 indicates that the vehicle’s control modules are unable to communicate over the main data network, known as the Controller Area Network (CAN) bus. The CAN bus is an internal communication system that links electronic control modules—such as the Engine Control Module (ECM), Transmission Control Module (TCM), and others—allowing them to exchange critical information. When this code is triggered, it means at least one module has been isolated from the network, disrupting normal vehicle operation. This issue can result in a variety of symptoms and may affect drivability or the functionality of multiple systems. Resolving it requires careful diagnosis, as the underlying causes range from simple wiring faults to malfunctioning modules.

Common symptoms for code U0073 #

Drivers or technicians may notice several warning signs if code U0073 is present. Since the CAN bus acts like the central nervous system for all vehicle electronics, any interruption can manifest in multiple ways. Some symptoms may be subtle, while others are immediately obvious.

• Multiple warning lights illuminated on the dashboard (ABS, Traction Control, Check Engine, etc.)
• Malfunction or loss of communication with one or more vehicle systems (e.g., ABS, transmission, power steering)
• Failure to start or intermittent starting issues
• Erratic or non-functional gauges and displays
• Loss of electronic features (e.g., cruise control, stability control)
• Communication errors during scan tool diagnostics (unable to access certain modules)

Most likely causes for code U0073 #

The majority of U0073 cases originate from issues affecting the integrity or operation of the CAN bus network. Causes range from physical wiring problems to internal module faults. Understanding the order of likelihood helps prioritize your inspection and repair efforts.

1. Faulty or corroded CAN bus wiring/connectors (due to moisture, damage, or poor connections)
2. Defective control module (any module on the CAN network, commonly ABS or BCM)
3. Aftermarket electronic installations (poorly installed alarms, remote starters, stereos)
4. Open circuit or short to ground/power in CAN bus wires
5. Blown fuses related to control modules
6. Low battery voltage or charging issues

Step-by-step diagnosis for U0073 #

Diagnosing U0073 requires both a systematic approach and familiarity with your vehicle’s CAN bus layout. Start with the basics, then proceed to more advanced tests if needed. Always ensure safety by disconnecting the battery when inspecting wiring.

1. Check for other related DTCs: Use a scan tool to identify all codes, not just U0073, and note which modules are not communicating.
2. Inspect battery voltage and connections: Ensure the battery is fully charged and connections are clean and secure.
3. Visually inspect CAN bus wiring and connectors: Look for corrosion, bent pins, moisture intrusion, or physical damage along harnesses, especially near module connectors and in high-moisture areas (like under carpets).
4. Check fuses and relays: Verify power supply to all relevant control modules.
5. Disconnect aftermarket devices: Temporarily remove or bypass any non-OEM electronics to rule out interference.
6. Perform continuity and resistance tests on CAN wires: Using a multimeter, check for open circuits and shorts between CAN High and CAN Low lines, as well as shorts to ground or battery voltage.
7. Module isolation test: If equipped, disconnect suspected modules one at a time (following OEM instructions) to see if the network communication is restored.
8. Consult OEM wiring diagrams and technical service bulletins (TSBs): Some vehicles have known issues or updated repair procedures that can save time.

Possible repairs for U0073 #

Once the root cause is identified, repairs can range from straightforward to complex. Address each underlying issue methodically, and always retest the system after repairs.

• Repair or replace damaged CAN bus wiring and connectors (clean corrosion, fix broken wires, replace connectors as needed)
• Replace faulty control module(s) (e.g., ABS control unit, Body Control Module)
• Remove or repair aftermarket electronics that interfere with the CAN network
• Replace blown fuses and rectify underlying causes
• Restore proper battery voltage (charge or replace battery, fix alternator issues)
• Update module software if a manufacturer TSB applies

Is it safe to drive with code U0073? #

In most cases, driving with U0073 is not recommended. This code indicates a significant communication breakdown between critical vehicle systems. While some vehicles may continue to run, you risk losing essential functions such as ABS, traction control, power steering, and even engine management. At best, you may lose convenience features; at worst, you may experience sudden system failures that compromise safety or leave you stranded.

Vehicles most commonly affected by U0073 #

Although any modern vehicle using a CAN bus can log U0073, it appears more frequently in certain makes and models, especially where wiring harness routing or module placement is more vulnerable.

• General Motors (Chevrolet, GMC, Cadillac, Buick)
• Ford (including Lincoln and Mercury)
• Honda and Acura
• Toyota and Lexus
• Hyundai and Kia
• Volkswagen and Audi
• Nissan and Infiniti

Common mistakes & best practices for U0073 #

Misdiagnosing U0073 is common, as it can be caused by anything from a simple blown fuse to a failed control module. Avoid jumping to conclusions without a thorough step-by-step inspection.

• Replacing control modules before checking wiring (always inspect and test wiring first)
• Ignoring battery or charging system health (low voltage can mimic or trigger communication faults)
• Overlooking aftermarket installations (non-OEM electronics often cause network issues)
• Missing related DTCs (always scan all modules, not just the ECM/PCM)
• Failing to clear codes and retest after repairs

U0073 FAQ #

Have more questions? Here are some quick answers to common concerns about code U0073.

• Q: Can a bad battery cause U0073?
  A: Yes. Low battery voltage or poor connections can disrupt communication between modules and trigger this code.
• Q: If my car starts and drives, can I ignore U0073?
  A: No. Even if the vehicle seems fine, hidden issues can escalate or cause sudden failures. It’s best to diagnose and repair as soon as possible.
• Q: Can I clear the code with a scan tool and keep driving?
  A: You can clear the code, but if the root cause isn’t fixed, it will likely return. Always address the underlying problem.