An open in the bus A CAN + or CAN - wire (OBD-Codes.com). A short to power or to ground in either bus A CAN wire (OBD-Codes.com). A general problem with the CAN bus network, including loose connections or broken wires (RepairPal). Corroded, burnt or damaged terminals in the network connectors (OBD-Codes.com). A dead or weak battery, or an intermittent glitch (RepairPal). A faulty control module; RepairPal lists this as a common cause, OBD-Codes.com says it is rare (OBD-Codes.com, RepairPal).

Repair open or shorted CAN bus wiring (OBD-Codes.com, RepairPal). Clean or repair corroded or damaged network connectors and terminals (OBD-Codes.com). Charge or replace a dead or weak battery, then clear the code (RepairPal). Restore power or ground to a module that isn't responding, or reprogram it (RepairPal). Replace a control module only after testing shows it is dragging the network down (OBD-Codes.com, RepairPal).

U0073🔧 Vehicle network (CAN bus)Stop and fix promptly

U0073: Control Module Communication Bus A Off (Meaning, Causes, Fixes)

Q: What does U0073 mean?

U0073 means the car's computer network, called the CAN bus, has shut down or stopped carrying messages on bus A, so one or more control modules can't communicate. Common causes are an open or shorted wire in the CAN bus, corroded or damaged network connectors, a dead or weak battery, or a faulty control module that is dragging the network down. Other U codes stored with it, such as U0100, usually point to which module is involved. Modern vehicles have many computers, called control modules, that share information over a two-wire network called the controller area network (CAN bus). Both OBD-Codes.com and RepairPal define U0073 as Control Module Communication Bus A Off: one or more modules can't communicate properly over CAN bus A. U0074 is the same fault on bus B. OBD-Codes.com says the code applies to most fuel-injected vehicles since 2004, including Acura, Buick, Chevrolet, Cadillac, Ford, GMC and Honda, and warns that a scan tool may not be able to talk to the car at all, depending on which circuit is affected. RepairPal explains that which physical bus counts as A depends on the manufacturer, and says the code is monitored while the vehicle is running and module supply voltage is normal. The sources disagree on the likely cause: OBD-Codes.com lists open or shorted CAN bus wiring first and says a faulty control module is rare, while RepairPal lists a faulty control module and a CAN bus problem as the two common causes. RepairPal also notes that a dead battery or an intermittent glitch can set it. OBD-Codes.com points to GM bulletin 08-07-30-021E, which applies to many 2007-2010 Cadillac, GMC, Chevrolet and Hummer vehicles. Related codes include U0074 (bus B off), U0100 (lost communication with the engine computer) and U0101 (lost communication with the transmission computer).

Q: Can I keep driving with U0073?

Stop and fix promptly. Get it checked soon, and treat it as serious if the car runs poorly. RepairPal rates U0073 Moderate, but both sources say the effects depend on which modules can't talk to each other: OBD-Codes.com lists lack of power, all the dash warning lights coming on and possibly a no-crank, no-start, and RepairPal lists problems ranging from a no-start to a dead HVAC system. If the engine loses power, the transmission acts up or several warning lights come on at once, stop driving and have it diagnosed rather than risk stalling in traffic.

Reviewed 2026-10-23 · Based on 2 cited source(s)

What U0073 means

Modern vehicles have many computers, called control modules, that share information over a two-wire network called the controller area network (CAN bus). Both OBD-Codes.com and RepairPal define U0073 as Control Module Communication Bus A Off: one or more modules can't communicate properly over CAN bus A. U0074 is the same fault on bus B. OBD-Codes.com says the code applies to most fuel-injected vehicles since 2004, including Acura, Buick, Chevrolet, Cadillac, Ford, GMC and Honda, and warns that a scan tool may not be able to talk to the car at all, depending on which circuit is affected. RepairPal explains that which physical bus counts as A depends on the manufacturer, and says the code is monitored while the vehicle is running and module supply voltage is normal. The sources disagree on the likely cause: OBD-Codes.com lists open or shorted CAN bus wiring first and says a faulty control module is rare, while RepairPal lists a faulty control module and a CAN bus problem as the two common causes. RepairPal also notes that a dead battery or an intermittent glitch can set it. OBD-Codes.com points to GM bulletin 08-07-30-021E, which applies to many 2007-2010 Cadillac, GMC, Chevrolet and Hummer vehicles. Related codes include U0074 (bus B off), U0100 (lost communication with the engine computer) and U0101 (lost communication with the transmission computer).

Severity: can I keep driving?

Stop and fix promptly

Get it checked soon, and treat it as serious if the car runs poorly. RepairPal rates U0073 Moderate, but both sources say the effects depend on which modules can't talk to each other: OBD-Codes.com lists lack of power, all the dash warning lights coming on and possibly a no-crank, no-start, and RepairPal lists problems ranging from a no-start to a dead HVAC system. If the engine loses power, the transmission acts up or several warning lights come on at once, stop driving and have it diagnosed rather than risk stalling in traffic.

Common symptoms

Check engine light on (OBD-Codes.com, RepairPal)
Other U codes stored that name a specific module that can't communicate (RepairPal)
All the instrument cluster warning lights on (OBD-Codes.com)
Lack of power or poor fuel economy (OBD-Codes.com)
Problems with whatever the affected modules control, from a no-start to an HVAC system that doesn't work (RepairPal)
Possibly a no-crank, no-start condition (OBD-Codes.com, RepairPal)

Likely causes

Roughly most to least common, based on the sources below. Your vehicle may differ.

An open in the bus A CAN + or CAN - wire (OBD-Codes.com)
A short to power or to ground in either bus A CAN wire (OBD-Codes.com)
A general problem with the CAN bus network, including loose connections or broken wires (RepairPal)
Corroded, burnt or damaged terminals in the network connectors (OBD-Codes.com)
A dead or weak battery, or an intermittent glitch (RepairPal)
A faulty control module; RepairPal lists this as a common cause, OBD-Codes.com says it is rare (OBD-Codes.com, RepairPal)

Diagnostic steps you can do

⚠ Before you start

Work on a cool engine, parked on level ground with the parking brake set. Never work under a car supported only by a jack.

Check for technical service bulletins for your vehicle; OBD-Codes.com points to GM bulletin 08-07-30-021E for many 2007-2010 GM vehicles (OBD-Codes.com, RepairPal).
Make sure the battery is charged and healthy, then clear the code and see if it returns, since RepairPal says it can be set by a dead battery or appear intermittently (RepairPal).
Note any other codes, especially other U codes. OBD-Codes.com says other module communication codes should be diagnosed first to avoid a misdiagnosis, and RepairPal says codes like U0100 point to the module involved.
Find the network connectors using a repair guide and inspect them and their wiring for chafing, bare wires, burn spots, melted plastic and corroded or green terminals (OBD-Codes.com).
Clean corroded terminals with electrical contact cleaner, let them dry, and apply dielectric grease before reconnecting (OBD-Codes.com).
If you have a multimeter, measure across the CAN High and CAN Low pins at the diagnostic port with the battery disconnected; RepairPal says about 60 ohms means both terminating resistors are intact (RepairPal).

Typical fixes

Repair open or shorted CAN bus wiring (OBD-Codes.com, RepairPal)
Clean or repair corroded or damaged network connectors and terminals (OBD-Codes.com)
Charge or replace a dead or weak battery, then clear the code (RepairPal)
Restore power or ground to a module that isn't responding, or reprogram it (RepairPal)
Replace a control module only after testing shows it is dragging the network down (OBD-Codes.com, RepairPal)

Repair costs vary widely by vehicle, region, parts brand and shop, so we don't quote prices. Get a written estimate after diagnosis.

🛠 When to call a pro

The car won't start, loses power or has several warning lights on at once (OBD-Codes.com, RepairPal)
Your scan tool can't communicate with the car (OBD-Codes.com)
Wiring and connector checks pass and the code keeps coming back; a shop can do a scan-tool roll call of the modules, unplug them one at a time, and test the network with a breakout box (RepairPal, OBD-Codes.com)
A module needs reprogramming or replacement (RepairPal)

Where to buy

Plain search links. Always match parts to your exact year, make, model and engine.

OBD2 scanners on Amazon Parts at Advance Auto Parts catalog at RockAuto

FAQs

Is U0073 serious?

It can be. RepairPal rates it Moderate, but because modules can't share information, OBD-Codes.com lists lack of power, all the warning lights on and possibly a no-start, and RepairPal says effects range from a no-start to an inoperative HVAC system depending on which modules are cut off.

Can a bad battery cause U0073?

Yes. RepairPal says U0073 can result from a dead battery or show up intermittently, so check the battery, clear the code and see if it comes back before going further.

Does U0073 mean a control module is bad?

Not necessarily. OBD-Codes.com says wiring opens and shorts are the usual causes and a faulty module is rare. RepairPal lists a faulty module as a common cause but adds that a module that won't communicate may just be missing power or ground or need reprogramming.

How much does it cost to fix U0073?

Neither source gives a repair cost. It can range from charging a battery or cleaning a connector to repairing network wiring or replacing a module, so get a diagnosis or a written estimate first.

Sources

Last reviewed 2026-10-23. Code definitions and repair steps can vary by manufacturer. Confirm with your vehicle's service information.