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Home / DTC / U351A — High Voltage System Interlock Circuit D Performance

U351A — High Voltage System Interlock Circuit D Performance

Detailed page for trouble code U351A.

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U351A

Generic U — Network/User

High Voltage System Interlock Circuit D Performance

Brand: Generic
Type: U — Network/User
Views: UK: 21 EN: 22 RU: 17
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Page language: EN

Causes

  • Open, short, or high-resistance in interlock wiring or connector
  • Corroded, loose or contaminated interlock connector or terminal
  • Faulty interlock switch, sensor, or service disconnect (charging inlet, HV junction box, service plug, etc.)
  • Faulty low-voltage supply or ground for the interlock circuit
  • Control module (BCM/VCM/HV controller) internal fault or software anomaly
  • Water intrusion or physical damage to harness near HV components

Symptoms

  • HV system disabled or limited (reduced power or limp mode)
  • Warning message(s) and HV warning indicator on instrument cluster
  • Vehicle may refuse to enter drive or will suddenly switch to a safe mode
  • Charging disabled or charge inlet not recognized
  • Possible intermittent faults or drives OK sometimes, fault other times

What to check

  • Record freeze-frame and active/confirmed status with a scan tool; note related codes and timestamps
  • Visually inspect interlock switch(es), service disconnect(s), charge inlet, and harness routing for damage or contamination
  • Check connectors for corrosion, bent pins, or loose terminals at both the interlock device and the control module
  • Verify fuses/relays and low-voltage supply and ground for the interlock circuit
  • Measure continuity and resistance of the interlock circuit with ignition off and HV system isolated per manufacturer procedures
  • Use a scan tool to monitor the interlock circuit status and compare live data to expected states while operating the interlock device

Signal parameters

  • Expected open-circuit continuity when service disconnect is removed; near 0 ohms when engaged (varies by design)
  • Typical control-signal voltages in the 0–12 V or 0–5 V range on low-voltage interlock sensing wires (consult vehicle-specific reference)
  • No unintended voltage to chassis ground on the interlock signal conductor
  • Resistance to ground should be high (open) on the signal conductor unless the circuit is designed to be pulled to ground when active
  • No rapid intermittent changes in the interlock status signal under steady conditions

Diagnostic algorithm

  1. SAFETY FIRST: Follow manufacturer high-voltage isolation and PPE procedures before working on HV components. Remove service disconnect or isolate HV battery per procedure.
  2. Retrieve and record all related DTCs, freeze-frame data, and current live data for the interlock circuit with a capable scan tool.
  3. Visually inspect the specific interlock device D (identify by wiring color or component location from wiring diagram), connectors, and associated harnesses for corrosion, damage, or moisture.
  4. With the vehicle powered down and HV system isolated, perform continuity and resistance checks from the interlock device terminals to the control module pins. Compare to specification.
  5. Check supply voltage and ground integrity for the interlock circuit at the control module connector with ignition on (per manual).
  6. Operate the interlock device (insert/remove service plug, open/close charge inlet lid, actuate latch/switch) while monitoring live data to confirm proper state changes. Note any delays, chatter, or no-change conditions.
  7. If intermittent, perform wiggle tests on harness and connectors while monitoring real-time data and watching for code recreation.
  8. If wiring and connectors pass, swap or bench-test the interlock switch/assembly if a known-good unit is available or replace the suspect interlock device.
  9. If suspect, inspect and repair connector terminals (re-pin, clean, replace) or repair damaged wiring sections; use proper sealing and corrosion protection.
  10. Clear codes, re-enable HV system per procedures, then perform a controlled functional test/road test and re-scan to confirm the fault does not return.
  11. If fault persists after component and wiring verification, capture detailed logs and consider controller/software update or module diagnosis by a dealer-level tool or manufacturer support.

Likely causes

  • Damaged or pushed-out terminal in the interlock connector
  • Intermittent connection at a service-disconnect plug or charge-port latch switch
  • Corrosion at connector pins where the interlock wiring mates
  • Short to chassis or to another circuit from chafed wiring
  • Failed interlock switch assembly

Fault status

⚠️ Status
Interlock Circuit D performance outside expected range — HV interlock monitoring indicates open, short, high resistance, or intermittent response; HV system may be disabled or limited until condition is corrected.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1.5-3.0 hours

Similar codes

U0100 U0140 P0A80 P0A7A U351B
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