Code
U0010
HYUNDAI
U — Network/User
Medium Speed CAN Communication Bus | CAN Communication Bus Off
Views:
UK: 20
EN: 41
RU: 45
AI status
Completed
Completed
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Causes
- Open or shorted CAN wiring (CAN H / CAN L).
- Corroded, loose, or damaged connectors at modules or splice points.
- Failed module that is forcing the bus off (internal short/transceiver failure).
- Missing or shorted termination resistor(s).
- Low battery voltage or poor battery connections during communication.
- Aftermarket electronics or improper repairs tapping the CAN bus.
Symptoms
- Loss of functions controlled by modules on the medium-speed CAN (e.g., lights, doors, HVAC, depending on vehicle).
- Multiple communication-related warnings or messages on cluster.
- Some modules not responding to a scan tool or showing ‘no communication’.
- Intermittent or permanent loss of subsystems tied to that bus.
- Possible drivability or safety-related warnings if related modules affected.
What to check
- Connect a capable scan tool and confirm U0010 and any related communication codes; record which modules are not responding.
- Check battery voltage and ground integrity (should be >12.2 V at rest).
- Visually inspect CAN wiring, connectors, and splice points for damage, corrosion, or aftermarket taps.
- Measure resistance across CAN H and CAN L at two far-apart points to check termination (~60 Ω expected for two 120 Ω terminators in parallel).
- Probe CAN H and CAN L with an oscilloscope or multimeter while cranking/idle to look for stuck dominant levels, shorts to Vb/GND, or excessive noise.
- Disconnect suspect modules one at a time (if safe and procedures permit) to see if the bus returns to normal.
Signal parameters
- Recessive idle voltages (typical): CAN H ≈ 2.4–2.6 V, CAN L ≈ 2.4–2.6 V (values may vary by manufacturer).
- Dominant state voltages (typical): CAN H ≈ 3.5–3.9 V, CAN L ≈ 1.0–1.5 V resulting in differential ≈ 2.0–2.5 V.
- Differential voltage (dominant) ≈ 1.5–2.5 V; differential (recessive) ≈ 0 V.
- Line-to-line resistance (bus idle): ~60 Ω (two 120 Ω terminators in parallel) — confirm vehicle-specific spec.
- Short checks: CAN H to battery positive (should be open), CAN L to ground (should be open).
Diagnostic algorithm
- Read and record all stored codes and freeze-frame data. Note which modules are not responding on the medium-speed CAN.
- Verify battery state of charge and clean/secure battery terminals and main grounds.
- Visually inspect wiring, connectors, and modules on the medium-speed CAN for damage or corrosion; repair any obvious issues.
- With key on, measure CAN H and CAN L voltages at a known good connector. Compare to expected idle values. If a line is stuck high or low, trace wiring toward modules to find short.
- Measure resistance across CAN H and CAN L at two locations to confirm correct termination (~60 Ω). If open or very low resistance, locate missing/shorted terminator.
- Use an oscilloscope to observe waveform quality: check for dominant stuck states, repeated errors, or noise. If bus is driven dominant continuously, identify and isolate the module driving the line.
- If no wiring fault is found, disconnect modules on the bus one at a time (following manufacturer safety and anti-theft procedures) to identify a module causing the bus off condition. Re-test after each disconnect.
- Repair or replace damaged wiring, connectors, or the faulty module as identified. Replace termination resistors if out of spec.
- Clear codes and perform a vehicle road/operation test to verify the issue is resolved and no new U-codes return.
- If problem persists after wiring and module checks, consult manufacturer technical service information for module-specific diagnostic procedures and consider module replacement or advanced network diagnostics.
Likely causes
- Short to battery or ground on CAN H or CAN L wiring.
- Failed CAN transceiver in one module causing bus to be held dominant.
- Open circuit or high resistance in CAN wiring or connector corrosion.
- Missing/failed termination resistors (incorrect resistance across bus).
Fault status
Status
Medium-speed CAN bus off condition detected. Communication to one or more modules on the medium-speed CAN network is interrupted or unavailable. Multiple systems on that network may be inoperative until the underlying wiring, termination, or module fault is repaired.
Repair difficulty: Medium
Diagnostic time: 1.5 - 4.0 hours
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