OBD-II trouble code
U0015: Medium Speed CAN Communication Bus (-) Open
The negative (CAN-Low) wire of the medium-speed communication bus has an open — a break, loose pin, or disconnected segment. Modules on that bus can no longer exchange messages reliably.
Quick facts
- System
- Network
- Category
- Network Communication
- Severity
- Medium severity
- Drivable
- Usually safe to drive short-term
- Repair cost range
- $100 – $700
- DIY difficulty
- Shop recommended
What does U0015 mean?
U0015 indicates an open circuit on the negative line — CAN-Low or CAN(-) — of the medium-speed CAN bus. Many vehicles run more than one communication network: a high-speed bus that links the critical powertrain, ABS, and stability modules, and a slower medium-speed bus that handles body, comfort, infotainment, and convenience modules where split-second timing matters less. U0015 is set when the CAN(-) wire on that medium-speed network is broken or disconnected, so the signal can no longer pass between the modules that share it.
A CAN bus carries data as the voltage difference between its two wires, CAN-High and CAN-Low. When CAN-Low goes open, that differential collapses or becomes intermittent and the modules downstream of the break stop hearing each other. Unlike a generic 'bus performance' code, U0015 points specifically at an open on the negative conductor — typically a cut or chafed wire, a corroded or backed-out terminal, a separated splice, or a connector that has worked loose. It is the CAN-Low counterpart of U0012 on the same medium-speed network, and the medium-speed counterpart to U0006 on the high-speed bus.
Because the medium-speed bus usually carries comfort and convenience functions rather than core driving systems, U0015 is generally less severe than a high-speed bus fault. The car will usually still start and drive, but you may lose features such as climate control, infotainment, power accessories, lighting functions, or driver displays, and several lost-communication U-codes may set together. It is diagnosed electrically — locating the open in the CAN(-) wiring — not by swapping modules on a guess.
Common causes
- Broken or cut CAN-Low wire on the medium-speed bus
- Corroded, loose, or backed-out terminal in a bus connector
- Separated or failed splice in the CAN(-) wiring
- Connector unplugged or not fully seated after prior service
- Water intrusion and corrosion opening the circuit intermittently
- Harness damage from rodents, road debris, or accident repair
- Internally failed module dropping the bus segment open
Symptoms
- One or more comfort/convenience features stop working (climate, infotainment, accessories)
- Driver information displays freeze, blank out, or show fault messages
- Multiple lost-communication U-codes stored alongside U0015
- Scan tool cannot reach modules on the medium-speed bus
- Intermittent feature loss that tracks with vibration or moisture
- Engine usually still starts and runs normally
Diagnostic steps
- 1.Scan every module and record all stored codes; the pattern of lost-communication codes helps show which bus segment is open.
- 2.Identify which modules sit on the medium-speed bus for the specific vehicle using wiring diagrams.
- 3.Key on, measure CAN-Low voltage along the bus; it should rest near 2.5 volts. A reading that goes open or floats past a certain point helps localize the break.
- 4.With key off and battery disconnected, check continuity of the CAN-Low wire between modules to find the open.
- 5.Inspect connectors and splices for corrosion, backed-out terminals, and water intrusion, especially after recent service.
- 6.Repair the open and clear the codes, then confirm the affected modules reappear on the scan tool and U0015 does not return.
Repair cost
$100 – $700
Diagnosis to locate the open commonly runs $100-$250. A wiring or connector repair to restore CAN-Low continuity is often $150-$500. If a failed module is breaking the bus, replacement with programming can run $400-$700+, higher on luxury and European platforms.
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.