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Home / DTC / U1011 — High Voltage Detected

U1011 — High Voltage Detected

Detailed page for trouble code U1011.

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Code

U1011

HYUNDAI U — Network/User

High Voltage Detected

Brand: HYUNDAI
Type: U — Network/User
AI status
Completed
ready
Completed 100%
Page language: EN

Causes

  • Faulty/high-voltage battery cells or cell group producing over-voltage
  • Battery Management System (BMS) sensor or monitor failure
  • Open/shorted voltage sensing circuit or damaged wiring/connectors
  • DC‑DC converter or onboard charger malfunction producing excessive output
  • HV relay/stage stuck closed or control circuit fault
  • Incorrect charger behavior (external charger overcharging)

Symptoms

  • Dashboard HV system warning or alarm (battery/charging warning)
  • Charge cycle stops or vehicle refuses to start charging
  • Reduced performance or limp/limitation mode engaged
  • Unexpected high pack voltage reading in live data
  • CAN communication or multiple HV-related DTCs present
  • Possible loss of DC‑DC function (12V charging issues)

What to check

  • Read all stored and pending DTCs and freeze-frame data from BMS, inverter, charger and vehicle network modules
  • Check for related codes (BMS, charger, inverter, DC‑DC converter, contactor/relay) and note timestamps
  • Visually inspect high‑voltage battery terminals, harnesses and HV connectors for damage, corrosion or overheating
  • Verify correct charging source and charging connector (check EVSE/charger settings)
  • Inspect HV fuses and contactors for welded contacts or abnormal wear
  • With appropriate PPE and procedures, measure total pack voltage at service disconnect and compare to expected nominal and maximum values

Signal parameters

  • Pack total voltage (V)
  • Pack current (A) and charge/discharge direction
  • Individual cell or module voltages (V) and min/max cell values
  • State of charge (SOC) and State of Health (SOH)
  • BMS reported pack voltage and voltage sensor readings
  • HV contactor/relay status (open/closed)

Diagnostic algorithm

  1. Obtain full DTC list from all HV-related modules and record freeze-frame data; do NOT attempt HV service without qualification
  2. If possible, clear code and re-run to see if code returns; note conditions when it returns (charging, driving, idle)
  3. Confirm vehicle is isolated and follow manufacturer HV safety procedure before measuring pack voltage or opening service disconnect
  4. Measure pack total voltage at service points with a calibrated meter; compare to nominal and maximum allowable voltages in service information
  5. Check individual cell/module voltages via diagnostic tool to identify over-voltage cells or imbalance
  6. Inspect and test HV charging equipment (onboard charger and external EVSE) to ensure it is not overvolting the pack
  7. Inspect HV wiring, connectors and contactors for shorts, opens or signs of overheating; test contactors for proper operation and resistance when closed
  8. Measure DC‑DC converter output to verify it is within specifications and not feeding excessive voltage back to pack circuitry
  9. Perform insulation/isolation resistance tests on HV wiring to rule out leakage or ground faults
  10. If wiring and external components check good, suspect BMS or voltage-sensing electronics — review BMS logs and perform targeted module tests per manufacturer procedure
  11. If a module (BMS, charger, DC‑DC, inverter) is found faulty, replace or repair per factory instructions and reconfigure/calibrate modules if required
  12. After repair, erase codes, perform system relearn/calibration steps, conduct charging and road tests to verify the fault does not recur

Likely causes

  • HV battery pack actual voltage above expected pack limit (overcharge or balancing failure)
  • Failed pack voltage sensor or harness shorted to battery potential
  • Onboard charger/EVSE delivering excessive voltage or failing to terminate charge
  • BMS internal electronic failure or corrupted calibration data
  • HV contactor/relay welded closed causing uncontrolled connection

Fault status

⚠️ Status
High-voltage system voltage exceeded expected limits or reported by BMS/charger. May disable charging, set limp mode or reduce vehicle function until serviced. Technician investigation required.
🔴 Repair difficulty: Hard
⏱️ Diagnostic time: 2.0-4.0 hours

Similar codes

U1010 U1000 U0100 P0A1E P0A1F
371

Browse 371 HYUNDAI manuals: repair procedures, diagnostics, wiring diagrams, component locations, service data and Labor Times by year, model and trim.

HYUNDAI

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Code

U1011

Other U — Network/User

SCP (J1850) Invalid or Missing Data for Engine Air Intake

Brand: Other
Type: U — Network/User
AI status
Completed
ready
Completed 100%
Page language: EN

Causes

  • Faulty/high-voltage battery cells or cell group producing over-voltage
  • Battery Management System (BMS) sensor or monitor failure
  • Open/shorted voltage sensing circuit or damaged wiring/connectors
  • DC‑DC converter or onboard charger malfunction producing excessive output
  • HV relay/stage stuck closed or control circuit fault
  • Incorrect charger behavior (external charger overcharging)

Symptoms

  • Dashboard HV system warning or alarm (battery/charging warning)
  • Charge cycle stops or vehicle refuses to start charging
  • Reduced performance or limp/limitation mode engaged
  • Unexpected high pack voltage reading in live data
  • CAN communication or multiple HV-related DTCs present
  • Possible loss of DC‑DC function (12V charging issues)

What to check

  • Read all stored and pending DTCs and freeze-frame data from BMS, inverter, charger and vehicle network modules
  • Check for related codes (BMS, charger, inverter, DC‑DC converter, contactor/relay) and note timestamps
  • Visually inspect high‑voltage battery terminals, harnesses and HV connectors for damage, corrosion or overheating
  • Verify correct charging source and charging connector (check EVSE/charger settings)
  • Inspect HV fuses and contactors for welded contacts or abnormal wear
  • With appropriate PPE and procedures, measure total pack voltage at service disconnect and compare to expected nominal and maximum values

Signal parameters

  • Pack total voltage (V)
  • Pack current (A) and charge/discharge direction
  • Individual cell or module voltages (V) and min/max cell values
  • State of charge (SOC) and State of Health (SOH)
  • BMS reported pack voltage and voltage sensor readings
  • HV contactor/relay status (open/closed)

Diagnostic algorithm

  1. Obtain full DTC list from all HV-related modules and record freeze-frame data; do NOT attempt HV service without qualification
  2. If possible, clear code and re-run to see if code returns; note conditions when it returns (charging, driving, idle)
  3. Confirm vehicle is isolated and follow manufacturer HV safety procedure before measuring pack voltage or opening service disconnect
  4. Measure pack total voltage at service points with a calibrated meter; compare to nominal and maximum allowable voltages in service information
  5. Check individual cell/module voltages via diagnostic tool to identify over-voltage cells or imbalance
  6. Inspect and test HV charging equipment (onboard charger and external EVSE) to ensure it is not overvolting the pack
  7. Inspect HV wiring, connectors and contactors for shorts, opens or signs of overheating; test contactors for proper operation and resistance when closed
  8. Measure DC‑DC converter output to verify it is within specifications and not feeding excessive voltage back to pack circuitry
  9. Perform insulation/isolation resistance tests on HV wiring to rule out leakage or ground faults
  10. If wiring and external components check good, suspect BMS or voltage-sensing electronics — review BMS logs and perform targeted module tests per manufacturer procedure
  11. If a module (BMS, charger, DC‑DC, inverter) is found faulty, replace or repair per factory instructions and reconfigure/calibrate modules if required
  12. After repair, erase codes, perform system relearn/calibration steps, conduct charging and road tests to verify the fault does not recur

Likely causes

  • HV battery pack actual voltage above expected pack limit (overcharge or balancing failure)
  • Failed pack voltage sensor or harness shorted to battery potential
  • Onboard charger/EVSE delivering excessive voltage or failing to terminate charge
  • BMS internal electronic failure or corrupted calibration data
  • HV contactor/relay welded closed causing uncontrolled connection

Fault status

⚠️ Status
High-voltage system voltage exceeded expected limits or reported by BMS/charger. May disable charging, set limp mode or reduce vehicle function until serviced. Technician investigation required.
🔴 Repair difficulty: Hard
⏱️ Diagnostic time: 2.0-4.0 hours

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