Code
U0011
Generic
U — Network/User
Medium Speed CAN Communication Bus Performance
Views:
UK: 25
EN: 38
RU: 24
AI status
Completed
Completed
100%
Causes
- Damaged or shorted CAN_H or CAN_L wiring
- Poor or corroded connectors or pins at module(s)
- Missing or failed termination resistor(s)
- Faulty CAN transceiver in one or more control modules
- A module holding the bus dominant (short to power/ground)
- Intermittent connections due to vibration or damaged insulation
Symptoms
- Malfunction Indicator Lamp (MIL) or communication warning
- Loss or intermittent operation of subsystems on the medium-speed CAN (e.g., body, comfort, instrument cluster features)
- Multiple communication-related DTCs or modules showing 'no response' on a scan tool
- Erratic or delayed instrument cluster messages, features that work intermittently
- Certain modules may enter a fail-safe or limp mode
What to check
- Connect a professional scan tool, read U-codes and note which modules report lost communication or timeouts
- Inspect connectors, pins, and harness routing for damage, corrosion, or recent service disturbance
- Check battery voltage and grounds; ensure stable supply (engine off and running where required)
- Measure DC resistance between CAN_H and CAN_L with ignition OFF (expected ≈ 60 Ω for two 120 Ω terminators in parallel; manufacturer may vary)
- Check for short to ground or battery on each CAN line with ohmmeter (power off)
- Perform wiggle test on harness while watching live data or DTCs for intermittent behavior
Signal parameters
- Nominal idle (recessive): CAN_H ≈ 2.5 V, CAN_L ≈ 2.5 V (both equal)
- Dominant state: CAN_H ≈ 3.5 V, CAN_L ≈ 1.5 V (differential ≈ 2.0 V)
- Differential voltage (dominant) ≈ 1.5–2.5 V, recessive ≈ 0 V
- Termination resistance across CAN_H and CAN_L ≈ 60 Ω (two 120 Ω terminators in parallel; verify manufacturer spec)
- Typical medium-speed CAN bus data rate often 125 kbps (check vehicle documentation — some systems use 62.5 or 250 kbps)
Diagnostic algorithm
- Use a scan tool: record U0011 and any related codes, note which modules are unresponsive or reporting errors.
- Check vehicle service information for medium-speed CAN topology, connector locations, and nominal bus speed/termination values.
- Visually inspect connectors, harnesses, and grounds along the medium-speed CAN network path; repair obvious faults.
- With ignition OFF, measure resistance between CAN_H and CAN_L at a convenient connector; expect ~60 Ω. If open or very low, investigate termination or short.
- With ignition ON, measure DC voltages on CAN_H and CAN_L relative to vehicle ground at a module connector; compare to expected idle levels (~2.5 V).
- Use an oscilloscope to view CAN_H and CAN_L waveforms while exercising the bus (crank, run, or operate systems as appropriate). Look for missing edges, excessive noise, distorted levels, or a node holding the bus dominant.
- If a suspect module is identified, disconnect it and re-check the bus. Isolating the module may restore normal bus behavior (do this per manufacturer safety/service procedures).
- Repair wiring/connector faults or replace failed transceiver/module as indicated. After repairs, clear codes and road-test to confirm the fault does not return.
- If no physical-layer faults are found, verify software/configuration updates and reflash or reprogram modules per manufacturer guidance.
Likely causes
- Open, short to ground, or short to battery on CAN_H or CAN_L
- Failed termination (expected ~60 Ω across H and L) or additional unintended termination
- One module actively driving the bus (shorted transceiver)
- Corroded multi-pin connector at a gateway or end-of-line module
- Intermittent harness damage near chassis harness clamps or door hinges
Fault status
Status
Medium Speed CAN communication bus performance fault detected. One or more nodes/messages on the medium-speed CAN network are not communicating reliably. Further physical-layer and module checks required.
Repair difficulty: Medium
Diagnostic time: 1.0-3.0 hours
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Code
U0011
HYUNDAI
U — Network/User
Medium Speed CAN Communication Bus Performance
Views:
UK: 24
EN: 23
RU: 14
AI status
Completed
Completed
100%
Causes
- Damaged or shorted CAN_H or CAN_L wiring
- Poor or corroded connectors or pins at module(s)
- Missing or failed termination resistor(s)
- Faulty CAN transceiver in one or more control modules
- A module holding the bus dominant (short to power/ground)
- Intermittent connections due to vibration or damaged insulation
Symptoms
- Malfunction Indicator Lamp (MIL) or communication warning
- Loss or intermittent operation of subsystems on the medium-speed CAN (e.g., body, comfort, instrument cluster features)
- Multiple communication-related DTCs or modules showing 'no response' on a scan tool
- Erratic or delayed instrument cluster messages, features that work intermittently
- Certain modules may enter a fail-safe or limp mode
What to check
- Connect a professional scan tool, read U-codes and note which modules report lost communication or timeouts
- Inspect connectors, pins, and harness routing for damage, corrosion, or recent service disturbance
- Check battery voltage and grounds; ensure stable supply (engine off and running where required)
- Measure DC resistance between CAN_H and CAN_L with ignition OFF (expected ≈ 60 Ω for two 120 Ω terminators in parallel; manufacturer may vary)
- Check for short to ground or battery on each CAN line with ohmmeter (power off)
- Perform wiggle test on harness while watching live data or DTCs for intermittent behavior
Signal parameters
- Nominal idle (recessive): CAN_H ≈ 2.5 V, CAN_L ≈ 2.5 V (both equal)
- Dominant state: CAN_H ≈ 3.5 V, CAN_L ≈ 1.5 V (differential ≈ 2.0 V)
- Differential voltage (dominant) ≈ 1.5–2.5 V, recessive ≈ 0 V
- Termination resistance across CAN_H and CAN_L ≈ 60 Ω (two 120 Ω terminators in parallel; verify manufacturer spec)
- Typical medium-speed CAN bus data rate often 125 kbps (check vehicle documentation — some systems use 62.5 or 250 kbps)
Diagnostic algorithm
- Use a scan tool: record U0011 and any related codes, note which modules are unresponsive or reporting errors.
- Check vehicle service information for medium-speed CAN topology, connector locations, and nominal bus speed/termination values.
- Visually inspect connectors, harnesses, and grounds along the medium-speed CAN network path; repair obvious faults.
- With ignition OFF, measure resistance between CAN_H and CAN_L at a convenient connector; expect ~60 Ω. If open or very low, investigate termination or short.
- With ignition ON, measure DC voltages on CAN_H and CAN_L relative to vehicle ground at a module connector; compare to expected idle levels (~2.5 V).
- Use an oscilloscope to view CAN_H and CAN_L waveforms while exercising the bus (crank, run, or operate systems as appropriate). Look for missing edges, excessive noise, distorted levels, or a node holding the bus dominant.
- If a suspect module is identified, disconnect it and re-check the bus. Isolating the module may restore normal bus behavior (do this per manufacturer safety/service procedures).
- Repair wiring/connector faults or replace failed transceiver/module as indicated. After repairs, clear codes and road-test to confirm the fault does not return.
- If no physical-layer faults are found, verify software/configuration updates and reflash or reprogram modules per manufacturer guidance.
Likely causes
- Open, short to ground, or short to battery on CAN_H or CAN_L
- Failed termination (expected ~60 Ω across H and L) or additional unintended termination
- One module actively driving the bus (shorted transceiver)
- Corroded multi-pin connector at a gateway or end-of-line module
- Intermittent harness damage near chassis harness clamps or door hinges
Fault status
Status
Medium Speed CAN communication bus performance fault detected. One or more nodes/messages on the medium-speed CAN network are not communicating reliably. Further physical-layer and module checks required.
Repair difficulty: Medium
Diagnostic time: 1.0-3.0 hours
Similar codes
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Code
U0011
MERCEDES-BENZ
U — Network/User
Medium Speed CAN Communication Bus Performance
Views:
UK: 16
EN: 23
RU: 15
AI status
Completed
Completed
100%
Causes
- Damaged or shorted CAN_H or CAN_L wiring
- Poor or corroded connectors or pins at module(s)
- Missing or failed termination resistor(s)
- Faulty CAN transceiver in one or more control modules
- A module holding the bus dominant (short to power/ground)
- Intermittent connections due to vibration or damaged insulation
Symptoms
- Malfunction Indicator Lamp (MIL) or communication warning
- Loss or intermittent operation of subsystems on the medium-speed CAN (e.g., body, comfort, instrument cluster features)
- Multiple communication-related DTCs or modules showing 'no response' on a scan tool
- Erratic or delayed instrument cluster messages, features that work intermittently
- Certain modules may enter a fail-safe or limp mode
What to check
- Connect a professional scan tool, read U-codes and note which modules report lost communication or timeouts
- Inspect connectors, pins, and harness routing for damage, corrosion, or recent service disturbance
- Check battery voltage and grounds; ensure stable supply (engine off and running where required)
- Measure DC resistance between CAN_H and CAN_L with ignition OFF (expected ≈ 60 Ω for two 120 Ω terminators in parallel; manufacturer may vary)
- Check for short to ground or battery on each CAN line with ohmmeter (power off)
- Perform wiggle test on harness while watching live data or DTCs for intermittent behavior
Signal parameters
- Nominal idle (recessive): CAN_H ≈ 2.5 V, CAN_L ≈ 2.5 V (both equal)
- Dominant state: CAN_H ≈ 3.5 V, CAN_L ≈ 1.5 V (differential ≈ 2.0 V)
- Differential voltage (dominant) ≈ 1.5–2.5 V, recessive ≈ 0 V
- Termination resistance across CAN_H and CAN_L ≈ 60 Ω (two 120 Ω terminators in parallel; verify manufacturer spec)
- Typical medium-speed CAN bus data rate often 125 kbps (check vehicle documentation — some systems use 62.5 or 250 kbps)
Diagnostic algorithm
- Use a scan tool: record U0011 and any related codes, note which modules are unresponsive or reporting errors.
- Check vehicle service information for medium-speed CAN topology, connector locations, and nominal bus speed/termination values.
- Visually inspect connectors, harnesses, and grounds along the medium-speed CAN network path; repair obvious faults.
- With ignition OFF, measure resistance between CAN_H and CAN_L at a convenient connector; expect ~60 Ω. If open or very low, investigate termination or short.
- With ignition ON, measure DC voltages on CAN_H and CAN_L relative to vehicle ground at a module connector; compare to expected idle levels (~2.5 V).
- Use an oscilloscope to view CAN_H and CAN_L waveforms while exercising the bus (crank, run, or operate systems as appropriate). Look for missing edges, excessive noise, distorted levels, or a node holding the bus dominant.
- If a suspect module is identified, disconnect it and re-check the bus. Isolating the module may restore normal bus behavior (do this per manufacturer safety/service procedures).
- Repair wiring/connector faults or replace failed transceiver/module as indicated. After repairs, clear codes and road-test to confirm the fault does not return.
- If no physical-layer faults are found, verify software/configuration updates and reflash or reprogram modules per manufacturer guidance.
Likely causes
- Open, short to ground, or short to battery on CAN_H or CAN_L
- Failed termination (expected ~60 Ω across H and L) or additional unintended termination
- One module actively driving the bus (shorted transceiver)
- Corroded multi-pin connector at a gateway or end-of-line module
- Intermittent harness damage near chassis harness clamps or door hinges
Fault status
Status
Medium Speed CAN communication bus performance fault detected. One or more nodes/messages on the medium-speed CAN network are not communicating reliably. Further physical-layer and module checks required.
Repair difficulty: Medium
Diagnostic time: 1.0-3.0 hours
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