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DTC codes / U00xx · Network wiring and bus faults / U0015

U0015Medium Speed CAN Communication Bus (-) Open

U0015 indicates that the medium-speed Controller Area Network (CAN) data bus has an open circuit on its negative or low-side conductor, preventing reliable communication between modules on that bus. The computer detects this when the CAN (-) wire is disconnected or has excessive resistance, causing missing or corrupted messages from one or more control modules.

SystemNetwork
Code typeGeneric (all makes)
SeverityMedium
Fix difficultyIntermediate
AreaNetwork wiring and bus faults

Symptoms you may notice

  • Illumination of the malfunction indicator lamp (MIL) or a communication fault message on the dashboard
  • Multiple warning lights (ABS, airbag, traction control) appearing simultaneously due to lost module communication
  • Intermittent or complete failure of systems such as the radio, climate control, or power windows that share the medium-speed bus
  • The engine may start and run normally, or the vehicle may enter a limp-home mode with reduced functionality
  • Often no symptoms besides the warning light, especially if the open is on a branch that serves non-critical modules
  • Intermittent operation of dashboard gauges or warning chimes

Common causes, most likely first

  1. A broken or chafed CAN (-) wire in the medium-speed bus harness, often at a flex point or near a connector
  2. Corroded or backed-out terminal in a CAN bus connector, especially at a module or splice pack
  3. Failed splice joint where multiple CAN (-) branches meet, causing an open to one or more modules
  4. Internal open circuit inside a control module that terminates the CAN (-) line
  5. Damage from rodent chewing, collision repair, or aftermarket accessory installation
  6. Water intrusion into a connector or module causing pin corrosion and an open circuit
  7. Loose or missing CAN bus termination resistor on the medium-speed bus, though this more often causes a different fault

How to diagnose and fix it

  1. Connect a scan tool and record all stored codes in every module to confirm U0015 is active and identify which modules are offline
  2. Obtain the vehicle-specific wiring diagram for the medium-speed CAN bus and locate the CAN (-) circuit, connectors, and splice points
  3. Perform a visual inspection of the harness and connectors for damage, corrosion, or loose pins, focusing on areas near the affected modules
  4. Measure resistance of the CAN (-) circuit from the data link connector (DLC) to each module and compare to specification, looking for an open
  5. Check for continuity between CAN (-) pins at the DLC and at each module connector while wiggling the harness to find intermittent opens
  6. Repair the open circuit by soldering and sealing the wire or replacing the affected connector terminal, then clear codes and verify communication
  7. If the open is internal to a module, replace or repair that module and recheck bus communication with a scan tool

What the CAN (-) open really means

  • U0015 refers specifically to the medium-speed CAN bus, which often runs at 125 kbps and connects body, comfort, and infotainment modules rather than the high-speed powertrain bus.
  • A single open on the CAN (-) line can take down multiple modules on that bus, so technicians must check all modules on the medium-speed network, not just the one reporting the code.
  • The code can be set by a module that is still communicating intermittently, so a wiggle test of the harness while watching live data is often more revealing than a static resistance check.
  • Aftermarket accessories tapped into the CAN bus, such as alarms or fleet trackers, are a commonly overlooked cause of an open or high-resistance CAN (-) circuit.
  • A faulty termination resistor or a module with an internal open can mimic a wiring open, so always isolate modules one at a time before condemning the harness.

Can I keep driving with U0015?

The vehicle may remain drivable if the open affects only comfort or body modules, but loss of communication can disable safety systems or cause unpredictable electrical behavior. Avoid driving if multiple warning lights are present or if the engine runs poorly, and have the fault diagnosed promptly.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

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

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