OBD-II trouble code
U0011: Medium Speed CAN Communication Bus (Performance)
The medium-speed CAN bus is communicating, but not reliably — messages are corrupted, intermittent, or out of spec. A 'performance' fault points to a degrading network rather than a fully dead one.
Quick facts
- System
- Network
- Category
- Network Communication
- Severity
- Medium severity
- Drivable
- Usually safe to drive short-term
- Repair cost range
- $100 – $1,000
- DIY difficulty
- Shop recommended
What does U0011 mean?
U0011 is the 'performance' version of a medium-speed CAN bus fault. Where a plain bus code means communication is broken, a performance code means the network is still talking but doing it poorly — the bus sees corrupted frames, a higher-than-allowed error rate, dropped messages, or signal levels that are out of specification. The medium-speed CAN bus (commonly around 125 kbps) typically links body and comfort modules such as the body control module, climate control, instrument cluster, radio, lighting, and door modules. When that network's signal quality degrades, a monitoring module stores U0011.
Performance faults are often the early or intermittent stage of the same problems that eventually cause a hard bus failure. A wire chafing against a bracket that only shorts when the body flexes, a terminal that has corroded just enough to add resistance, a marginal terminating resistor, water slowly wicking into a connector, or a module that occasionally transmits malformed messages will all degrade signal quality without fully killing the bus. Electrical noise from a failing component or a poor ground can also corrupt frames. Because the fault is intermittent or marginal, it can be one of the harder communication problems to pin down.
The symptoms usually show up in the body and comfort systems on this bus — features that work most of the time but occasionally glitch, reset, or drop out, sometimes triggered by bumps, temperature, or humidity. The engine and transmission normally live on the separate high-speed bus, so the car typically still starts and drives, making U0011 a medium-severity, driveable fault. Because it is intermittent, capturing the fault when it happens — with a scan tool's communication error counters or an oscilloscope — is often the key to diagnosis.
Common causes
- Intermittent short on a medium-speed CAN wire (chafing that only contacts when the body flexes)
- Corroded or high-resistance terminal adding noise to the bus
- Marginal or partially failed terminating resistor
- Water slowly wicking into a connector or harness
- A module intermittently transmitting corrupted messages
- Electrical noise from a failing component or poor ground
- Loose or backed-out terminal that makes contact only sometimes
- Damaged harness section that flexes with road vibration
Symptoms
- Body or comfort features that glitch, reset, or drop out intermittently
- Climate control, lighting, or radio behaving erratically now and then
- Warning messages or chimes that come and go
- Power accessories occasionally slow to respond or unresponsive
- Communication error counters rising on a scan tool
- Symptoms that track with bumps, temperature, or humidity
- Engine usually starts and runs normally
Diagnostic steps
- 1.Record all stored codes in every module and note which report communication errors — the pattern helps localize the degrading segment.
- 2.Use the wiring diagram to identify the medium-speed bus wires and modules on this specific vehicle.
- 3.Check the bus's communication error counters with a scan tool while wiggling harness sections and flexing connectors to provoke the intermittent fault.
- 4.Measure resistance across the medium-speed CAN pair and compare with the manufacturer's termination spec.
- 5.Inspect connectors and harness routing for partial corrosion, chafing, and water intrusion — door jambs and under-dash areas are common.
- 6.Use an oscilloscope on the bus to catch corrupted frames and identify a module sending malformed data when the fault appears.
Repair cost
$100 – $1,000
Diagnosis can be the larger cost here — $150-$350 or more — because intermittent bus performance faults take time to provoke and capture. Repairing a chafed wire, corroded terminal, or water-damaged connector typically runs $150-$500. Replacing a marginal terminating resistor is cheaper; replacing a module that intermittently corrupts the bus, including programming, runs $300-$900.
Estimate your repair
Run the numbers for your vehicle
Open the Repair Cost Estimator with module communication / can bus diagnosis preselected. Adjust labor rate and vehicle category to fit your situation.
DIY vs shop
Leave this one to a qualified shop. It typically involves emissions-critical components, refrigerant handling, or other work that requires manufacturer-grade tooling, training, or certification. DIY attempts often produce a more expensive problem than the original code.