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Home / DTC / U351B — High Voltage System Interlock Circuit D Low

U351B — High Voltage System Interlock Circuit D Low

Detailed page for trouble code U351B.

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Code

U351B

Generic U — Network/User

High Voltage System Interlock Circuit D Low

Brand: Generic
Type: U — Network/User
Views: UK: 26 EN: 24 RU: 25
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Page language: EN

Causes

  • HV interlock switch D stuck closed or mechanically failed
  • Short to ground in interlock circuit D wiring or connector
  • Damaged wiring harness (chafing, corrosion, water ingress)
  • Faulty or improperly seated interlock connector (loose pins/corrosion)
  • Faulty vehicle control module or BMS input circuit
  • Aftermarket modifications or improper reassembly after service

Symptoms

  • HV system disabled or inhibited (vehicle will not enable HV components)
  • Loss of propulsion or inability to charge HV battery
  • DTC U351B stored in fault memory; possible MIL or dash warning
  • Intermittent faults when vehicle doors, trunks, or service plugs are moved
  • Visible corrosion or moisture near interlock components

What to check

  • Verify stored freeze frame and related DTCs; record conditions when fault set
  • Visually inspect interlock switch D, associated connectors and harness for damage, corrosion, or water intrusion
  • With vehicle off and HV system safe/isolated per manufacturer procedures, check connector pin condition and seating
  • Measure voltage at the interlock circuit pin at the control module and at the switch/connector while operating the switch (observe safety rules)
  • Check continuity to chassis ground from the interlock circuit with ignition off to confirm unintended grounding
  • Review wiring diagram to confirm correct routing and any splices or junctions that could cause shorts

Signal parameters

  • Normal open state (depending on design): ~4.5–5.5 V on 5V reference systems, or ~9–13 V on 12V reference systems
  • Low/closed state: 0–0.5 V (ground) or continuity to chassis ground
  • Expected continuity when closed: ~0–2 ohms between switch terminals (verify with spec)
  • Expected open circuit when switch open: high resistance/infinite
  • Confirm actual system reference voltage from wiring diagram before testing

Diagnostic algorithm

  1. Read and record U351B and any related codes (other U or BMS codes). Clear codes, perform functional test, and see if code returns.
  2. Visually inspect interlock switch D, harness, and connectors for damage, corrosion, water, or loose pins. Repair or replace any damaged connectors or wiring.
  3. With vehicle in a safe state and following HV safety procedures, operate the interlock (open/close) while monitoring the circuit voltage at the module and at the switch/connector. Confirm voltage transitions between low (0 V) and high (reference voltage) as expected.
  4. If signal remains low, isolate sections of the harness: disconnect the interlock switch, check for continuity to ground on the harness side. If continuity to ground exists with switch disconnected, repair harness short to ground.
  5. If harness is good and switch tests correctly, confirm module input wiring and ground. Check for shorted input inside control module if wiring intact.
  6. Repair or replace the faulty component (switch, harness, connector, or control module) as appropriate. Reassemble, clear codes, and perform system enable/functional tests to confirm the fault does not return.
  7. If intermittent, subject interlock and connectors to movement and environmental test (light spray/dry conditions per manufacturer guidelines) to reproduce fault before final repair.

Likely causes

  • Moisture/corrosion at interlock connector causing low/grounded signal
  • Interlock switch D physically shorted or jammed closed
  • Pinched/chafed harness contacting chassis ground
  • Connector pin pushed out or cross‑mated causing continuity to ground
  • Internal control module input short or failed input driver

Fault status

⚠️ Status
High Voltage System Interlock Circuit D reports a low/grounded condition. HV interlock is not in the expected state; HV system may be disabled.
🔴 Repair difficulty: Hard
⏱️ Diagnostic time: 1.0-3.0 hours

Similar codes

U351A U351C U351D U3520 U0100
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