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Home / DTC / U351C — High Voltage System Interlock Circuit D High

U351C — High Voltage System Interlock Circuit D High

Detailed page for trouble code U351C.

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U351C

Generic U — Network/User

High Voltage System Interlock Circuit D High

Brand: Generic
Type: U — Network/User
Views: UK: 18 EN: 34 RU: 20
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Page language: EN

Causes

  • Open or high-resistance wiring in HV interlock circuit D
  • Short to battery positive (B+) at interlock harness or connector
  • Corroded, loose, or damaged interlock connector(s) or terminals
  • Service plug, isolation device, or interlock switch not fully seated or damaged
  • Faulty interlock sensor/switch assembly
  • Faulty HV battery pack connector or enclosure seal causing open/invalid reading

Symptoms

  • HV system disabled or inhibited; vehicle may refuse to enter EV/drive mode
  • HV warning light, master warning, or MIL illuminated
  • Reduced propulsion or limp-home mode
  • Charging disabled or charging error
  • Stored U351C (and possibly related) DTC(s)
  • Possible audible relay/contactor click repeated or no contactor closure

What to check

  • Read freeze frame and full DTC list with a capable scan tool; record related codes
  • Confirm vehicle safety: follow HV isolation procedures before touching HV components
  • Visual inspection of HV battery service plug, interlock connector(s), and harness for damage, corrosion, water ingress or poor seating
  • Check that service plug / isolation handle is fully inserted and latched
  • Backprobe interlock circuit D pin at engine/controller connector with ignition ON (following safety rules) and measure voltage
  • Check continuity from interlock connector pin to the HV battery/interlock switch; measure resistance

Signal parameters

  • Typical interlock circuit logic: closed/safe = low voltage (near 0 V), open/fault = high voltage (near reference or 5 V) — exact values depend on manufacturer
  • Expected idle voltage range (example): 0–0.5 V when interlock closed; ~4.5–5 V or open-circuit when open/fault. Verify with OEM specs
  • Continuity when closed: low resistance (typically
  • Watch for intermittent spikes or floating voltages when wiggling harness/connectors

Diagnostic algorithm

  1. Retrieve and record all DTCs and freeze frame data. Note ignition state and battery voltages when code set.
  2. Follow manufacturer HV safety procedures. Disable HV system and remove service plug before probing live HV conductors/hardware.
  3. Visually inspect the HV battery enclosure, service plug, interlock switch, intermediate connectors and harness for corrosion, loose pins, water ingress, or physical damage.
  4. With ignition ON (and HV safety observed), backprobe the interlock circuit D signal at the controller/connector and measure voltage. Compare to expected low/high values from signal_params.
  5. If voltage is high/open, measure continuity between the controller pin and the HV interlock device (battery pack/service plug). If open, locate and repair the break or poor connection.
  6. If continuity is present but voltage still abnormal, check for short to B+ on the interlock harness (insulation damage) using resistance-to-battery or voltage tests with HV system inert as required by procedures.
  7. Inspect and test the interlock switch/sensor assembly: operate the service plug/handle and verify the signal changes state reliably. Replace the switch/sensor if it fails to change state.
  8. Repair or replace damaged connector terminals, pins, or harness sections. Clean corrosion and reseat connectors; use OEM-rated HV repair parts and seals.
  9. If wiring and switch are good, check inputs at the HV ECU/module. If signal is correct at the interlock device but not at the ECU, suspect wiring damage between or ECU fault.
  10. After repairs, clear codes, perform key on/self-test and verify code does not return. Road test or operate charging to confirm normal HV operation.
  11. If the code persists after wiring and component checks, consult OEM wiring diagrams and consider module replacement or module reflash as a last step.

Likely causes

  • Disconnected or corroded interlock connector at HV battery or junction
  • Service plug or safety latch not fully inserted or has damaged contacts
  • Damaged wiring harness (cut, chafed, melted) causing intermittent/open circuit
  • Interlock switch/sensor failed (contacts stuck open)
  • Short to B+ at harness pin or nearby high-voltage conductor

Fault status

⚠️ Status
High Voltage System Interlock Circuit D reports a high/open condition. HV system safety interlock may be open, preventing HV enablement. Inspect interlock connectors, wiring, service plug and interlock switch.
🔴 Repair difficulty: Hard
⏱️ Diagnostic time: 1.0-3.0 hours

Similar codes

U351B U351D U0100 U0121 P0AFA
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