Broken or chafed wire in the positive bus circuit, often at a flex point or near a connector; Corroded or backed-out terminal in a bus connector, creating an open circuit; Failed splice or junction point within the wiring harness where bus segments meet; Damaged control module connector or internal module fault that opens the bus positive line; Aftermarket accessory installation that cut or disturbed a bus wire; Rodent damage or physical impact that severed the bus conductor

DTC codes / U00xx · Network wiring and bus faults / U008B

U008BVehicle Communication Bus G (+) Open

Q: What does code U008B mean?

Vehicle Communication Bus G (+) Open. U008B is a generic network communication code indicating that a control module has detected an open circuit on the positive side of a vehicle communication bus, often a Controller Area Network (CAN) data line. The computer is reporting that the bus wire it expects to carry a signal is electrically disconnected or broken, preventing normal data exchange between modules.

U008B is a generic network communication code indicating that a control module has detected an open circuit on the positive side of a vehicle communication bus, often a Controller Area Network (CAN) data line. The computer is reporting that the bus wire it expects to carry a signal is electrically disconnected or broken, preventing normal data exchange between modules.

SystemNetwork

Code typeGeneric (all makes)

SeverityMedium

Fix difficultyProfessional

AreaNetwork wiring and bus faults

Symptoms you may notice

Illumination of the malfunction indicator lamp (MIL) or a dedicated communication fault light
Multiple warning lights on the dashboard, such as ABS, traction control, or airbag, because several modules lose communication
Intermittent or complete failure of systems that rely on shared bus data, including instrument cluster, transmission shifting, or stability control
Engine may start and run but enter a default or limp mode with reduced performance
No symptoms besides the warning light if the open circuit affects a non-critical segment of the bus
Random electrical gremlins such as flickering lights or inoperative accessories that share the same network

Common causes, most likely first

Broken or chafed wire in the positive bus circuit, often at a flex point or near a connector
Corroded or backed-out terminal in a bus connector, creating an open circuit
Failed splice or junction point within the wiring harness where bus segments meet
Damaged control module connector or internal module fault that opens the bus positive line
Aftermarket accessory installation that cut or disturbed a bus wire
Rodent damage or physical impact that severed the bus conductor

How to diagnose and fix it

Connect a scan tool and record all stored codes and live data to confirm U008B and identify which modules are offline
Obtain the vehicle-specific wiring diagram and locate the bus positive circuit, including all connectors and splices
Perform a visual inspection of the harness for chafing, corrosion, rodent damage, or loose connectors along the affected bus segment
Use a digital multimeter to check continuity and resistance on the bus positive wire from end to end, isolating the open section
Disconnect modules one at a time and recheck bus continuity to determine whether a module or the wiring is causing the open
Repair the open circuit by soldering and sealing the wire or replacing the affected harness section, then clear codes and verify communication
If the open is internal to a module, replace or reprogram that module according to manufacturer procedures and retest the network

What the bus open really means

U008B often appears after a battery replacement or jump-start when a module fails to wake up and reports the bus as open, so always check battery voltage and module power feeds first.
A single open on the positive bus line can take down multiple modules, but the code may be stored only in the module that detected the loss, leading technicians to replace the wrong component.
Aftermarket alarms, remote starters, or dash cams tapped into bus wiring are a frequent cause of an open circuit that owners overlook when diagnosing U008B.
The code does not always mean the bus wire itself is broken; a failed module that internally disconnects the bus positive pin can set the same code, so module isolation testing is essential.
On some vehicles, the bus positive circuit passes through a connector behind the kick panel or under the seat where corrosion from water leaks creates an intermittent open that only appears when the harness is flexed.

Can I keep driving with U008B?

If the vehicle starts and runs without obvious loss of critical systems, you can drive it cautiously to a repair shop, but avoid long trips and be prepared for sudden loss of dashboard or safety systems. If multiple warning lights are on or the engine runs poorly, stop driving and have the vehicle towed to prevent unsafe operation.

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.