Damaged or corroded wiring in the communication bus, such as a broken wire or poor connection at a connector; A faulty module on the bus that is shorting the network, preventing communication; Low battery voltage or a failing charging system causing modules to drop offline; Water intrusion or physical damage to the bus wiring harness; Failed termination resistors within a module, disrupting signal integrity; Aftermarket electronics improperly installed and interfering with the bus

DTC codes / U00xx · Network wiring and bus faults / U0028

U0028Vehicle Communication Bus A

Q: What does code U0028 mean?

Vehicle Communication Bus A. U0028 is a generic network communication code indicating that the vehicle's primary communication bus, typically the high-speed Controller Area Network (CAN), has experienced a general failure or loss of signal. The computer sets this code when it cannot reliably exchange data with other modules on that bus, often due to wiring faults, module failures, or power supply issues.

U0028 is a generic network communication code indicating that the vehicle's primary communication bus, typically the high-speed Controller Area Network (CAN), has experienced a general failure or loss of signal. The computer sets this code when it cannot reliably exchange data with other modules on that bus, often due to wiring faults, module failures, or power supply issues.

SystemNetwork

Code typeGeneric (all makes)

SeverityHigh

Fix difficultyProfessional

AreaNetwork wiring and bus faults

Symptoms you may notice

Multiple warning lights illuminated simultaneously, including the check engine light, ABS, and airbag lights
The engine may start but run poorly or stall, or the vehicle may fail to start at all
Inoperative dashboard gauges, such as the speedometer or fuel gauge
Transmission may default to limp mode or fail to shift properly
Often no symptoms besides the warning light, especially if the fault is intermittent
Other electronic features like power windows, radio, or climate control may behave erratically

Common causes, most likely first

Damaged or corroded wiring in the communication bus, such as a broken wire or poor connection at a connector
A faulty module on the bus that is shorting the network, preventing communication
Low battery voltage or a failing charging system causing modules to drop offline
Water intrusion or physical damage to the bus wiring harness
Failed termination resistors within a module, disrupting signal integrity
Aftermarket electronics improperly installed and interfering with the bus

How to diagnose and fix it

Perform a thorough visual inspection of the communication bus wiring and connectors for damage, corrosion, or loose pins
Check battery voltage and charging system output to ensure stable power to all modules
Use a scan tool to retrieve all stored codes from every module and identify which modules are not communicating
Measure resistance across the bus lines (CAN High and CAN Low) to check for proper termination and shorts
Disconnect modules one by one to see if communication is restored, isolating a faulty module
Repair or replace any damaged wiring or connectors found during inspection
If a module is suspected, test it on a bench or substitute with a known-good unit before replacement

Before you replace the BCM or PCM

A weak battery is a very common cause of U0028; modules may boot up but fail to communicate reliably if voltage drops during cranking.
Aftermarket alarms or remote starters tapped into the bus wiring often introduce noise or shorts that set this code.
The code can be set by a single module holding the bus low, so disconnecting modules one at a time is a fast way to isolate the culprit.
U0028 does not always mean the bus is dead; intermittent faults from chafed wires can set it without any current driveability issue.
Some vehicles require programming of a replacement module to the bus, so swapping parts without proper setup can introduce new communication codes.

Can I keep driving with U0028?

If the vehicle starts and runs, limit driving to a short distance to a repair shop, as communication failures can cause unpredictable stalling or loss of critical systems. If the engine will not start or multiple safety systems are disabled, do not drive and have the vehicle towed.

Tools that help

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