Poor electrical connections at a medium-speed CAN bus module, including loose or corroded connectors and damaged pins.; Chafed, pinched, or intermittently shorted CAN bus wiring, often near a hinge, grommet, or high-vibration area.; A failing module on the medium-speed CAN bus that is corrupting bus traffic or holding the bus in a fault state.; Low or unstable battery voltage, or a weak ground connection, causing modules to drop off the bus intermittently.; Aftermarket electronics improperly tapped into the CAN bus wiring, introducing noise or improper termination.; Water intrusion into a connector or module on the medium-speed bus, leading to intermittent performance faults.; A faulty CAN bus termination resistor inside one of the modules on that bus, altering bus impedance.

DTC codes / U00xx · Network wiring and bus faults / U0011

U0011Medium Speed CAN Communication Bus (Performance)

Q: What does code U0011 mean?

Medium Speed CAN Communication Bus (Performance). U0011 is a generic network code indicating that the medium-speed Controller Area Network (CAN) bus is not performing as expected, meaning the modules on that bus cannot reliably exchange data. The computer detected a performance fault, such as excessive bus errors, missing messages, or a bus that stays in a degraded state, rather than a simple open or short circuit.

U0011 is a generic network code indicating that the medium-speed Controller Area Network (CAN) bus is not performing as expected, meaning the modules on that bus cannot reliably exchange data. The computer detected a performance fault, such as excessive bus errors, missing messages, or a bus that stays in a degraded state, rather than a simple open or short circuit.

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 network warning light.
Often no symptoms besides the warning light, with all accessories and driving functions working normally.
Intermittent or simultaneous warning lights for anti-lock brakes, airbags, or traction control.
Erratic operation of body control functions such as power windows, door locks, or interior lighting.
The engine may start and run, but some convenience features or driver-assist systems become unavailable.
A stored U0011 alone with no drivability complaint, especially after a battery replacement or jump start.

Common causes, most likely first

Poor electrical connections at a medium-speed CAN bus module, including loose or corroded connectors and damaged pins.
Chafed, pinched, or intermittently shorted CAN bus wiring, often near a hinge, grommet, or high-vibration area.
A failing module on the medium-speed CAN bus that is corrupting bus traffic or holding the bus in a fault state.
Low or unstable battery voltage, or a weak ground connection, causing modules to drop off the bus intermittently.
Aftermarket electronics improperly tapped into the CAN bus wiring, introducing noise or improper termination.
Water intrusion into a connector or module on the medium-speed bus, leading to intermittent performance faults.
A faulty CAN bus termination resistor inside one of the modules on that bus, altering bus impedance.

How to diagnose and fix it

Verify battery voltage and condition, and check that the charging system is stable, because low voltage is a common trigger for network performance codes.
Inspect all medium-speed CAN bus connectors for corrosion, loose pins, and water intrusion, then clean and reseat them.
Perform a visual inspection of the CAN bus wiring harness for chafing, pinches, or repairs, especially near moving components.
Use a scan tool to read live network data and check for other modules that are offline or reporting communication faults on the same bus.
Measure CAN bus resistance and voltage at the diagnostic link connector (DLC) to confirm bus integrity and termination.
Isolate modules one at a time by disconnecting them to see if the performance fault clears, identifying a faulty module.
Repair or replace damaged wiring, connectors, or the faulty module, then clear codes and verify the repair with a road test.

What a medium-speed CAN fault really means

A U0011 can be set by a module that is not on the medium-speed bus itself, because a gateway module may report the performance fault when it cannot relay messages between buses.
Many U0011 codes appear after a dead battery or jump start, when modules boot up in an unexpected order and log a performance fault that never returns after clearing.
A single faulty module can pull the entire medium-speed bus down, so disconnecting modules one at a time is often faster than chasing wiring.
Aftermarket alarms, remote starters, and dash cameras tapped into CAN wiring are frequent culprits that owners overlook.
The code does not always mean the bus is dead; it can be stored intermittently from a momentary glitch, so a wiggle test of harnesses is essential.

Can I keep driving with U0011?

The vehicle is usually safe to drive if it starts, runs, and has normal brakes and steering, but avoid long trips and do not ignore additional warning lights that appear. If multiple systems fail or the engine runs poorly, stop driving and have the vehicle towed for diagnosis.

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.