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Home / DTC / U0015 — Medium Speed CAN Communication Bus (-) Open

U0015 — Medium Speed CAN Communication Bus (-) Open

Detailed page for trouble code U0015.

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U0015

Generic U — Network/User

Medium Speed CAN Communication Bus (-) Open

Brand: Generic
Type: U — Network/User
Views: UK: 14 EN: 24 RU: 17
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Page language: EN

Causes

  • Open or broken CAN- wire in harness
  • Corroded, bent, or poorly seated connector pins on CAN- terminals
  • Damaged CAN bus transceiver in a module
  • Short or intermittent connection to battery positive or ground affecting CAN-
  • Failed module pulling the bus to an open or invalid state
  • Missing or incorrect termination resistor(s) on the medium-speed CAN network

Symptoms

  • MIL (check engine light) or communication related warning lamp illuminated
  • Loss of functions controlled by modules on the medium-speed CAN network (e.g., body modules, gateways, sensors)
  • Intermittent or permanent module communication faults on scan tool
  • Multiple U‑codes or dependent DTCs for modules that cannot be reached
  • No data or timeout when requesting data from modules on the MS CAN network

What to check

  • Scan for all U‑codes and module-specific COMM codes; note modules reporting loss of communication
  • Visually inspect CAN wiring, connectors, and harness routing for damage, corrosion, abrasions, or rodents
  • Verify relevant fuses and power/ground for modules on this CAN network
  • Check connector seating at gateway/module junctions and any splice boxes
  • Measure resistance across CAN H and CAN L at key connector points (expected ~60 Ω with network intact)
  • Use a multimeter or oscilloscope to measure idle voltages on CAN- and CAN+ at multiple nodes

Signal parameters

  • Recessive state: CAN+ ≈ 2.5 V, CAN- ≈ 2.5 V (both lines near mid‑rail)
  • Dominant state: CAN+ ≈ 3.5 V, CAN- ≈ 1.5 V (differential ~2.0 V)
  • Bus differential (dominant) ≈ 2.0 V
  • Termination resistance: ≈ 60 Ω measured across CAN H and CAN L with network connected (two 120 Ω terminators in parallel)
  • Typical medium-speed CAN baud rate: commonly 125 kbps (verify vehicle-specific rate)

Diagnostic algorithm

  1. Connect a diagnostic scan tool; record U0015 and related codes and freeze frame data. Check for multiple network faults.
  2. Identify all modules on the medium-speed CAN network and note their connector/power/ground locations from wiring information.
  3. Visually inspect wiring, connectors, harnesses, and splice points for damage, corrosion, pin push‑out or moisture at each module and gateway.
  4. Verify fuses and module power/grounds. Repair any lost power or poor ground before further testing.
  5. With ignition on, measure idle voltages at CAN+ and CAN- at a convenient connector near the gateway and at remote modules; compare to expected values.
  6. Measure DC resistance across CAN H and CAN L at several points. If resistance is very high or open, suspect an open circuit; if low to ground or battery, suspect short.
  7. Use a scope to view waveforms at multiple nodes while bus is active. Look for missing transitions on CAN-, missing dominant pulses, or flatline on CAN-.
  8. If short/open not localized, disconnect modules one at a time (unplug) while monitoring bus resistance/voltages to identify module causing open or loading the line.
  9. Repair or replace damaged wiring, connectors, or terminals. Replace faulty module transceivers only after isolating the bad module. Ensure proper reconnection and corrosion protection.
  10. Reinstall proper termination resistors if missing or incorrect. Clear codes, perform key-on and test drive, and verify code does not return and all modules communicate normally.

Likely causes

  • Broken/chafed CAN- conductor between modules
  • Disconnected or corroded connector at a gateway or module
  • Failed CAN transceiver in one module (internal open)
  • Open splice or poor crimp in harness splice box
  • Removed or incorrect termination (open 60 Ω across bus)
  • Blown fuse or lost power/ground to a module that provides CAN- continuity

Fault status

⚠️ Status
Medium Speed CAN bus (CAN-) open — loss of communication on the negative CAN line (open circuit detected).
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1.5 - 3.0 hours

Similar codes

U0100 U0101 U0073 U0121 U0140
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