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Home / DTC / U3528 — High Voltage System Interlock Circuit G High

U3528 — High Voltage System Interlock Circuit G High

Detailed page for trouble code U3528.

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U3528

Generic U — Network/User

High Voltage System Interlock Circuit G High

Brand: Generic
Type: U — Network/User
Views: UK: 18 EN: 26 RU: 17
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Page language: EN

Causes

  • Open or shorted interlock wiring (Circuit G)
  • Corroded, loose or damaged connector at interlock switch or harness
  • Failed interlock switch/sensor or built-in resistor
  • Short to battery positive (12 V) or to another high potential on the interlock signal
  • Poor ground or high resistance in return path
  • Water intrusion or contamination at connector/switch

Symptoms

  • HV system disabled or limited (no HV drive or charging inhibited)
  • HV/Service/Check Hybrid/Electrical system warning lamp illuminated
  • Reduced vehicle performance or no-start condition for EV/HEV systems
  • Stored U3528 code and possibly related interlock or isolation fault codes
  • Vehicle may enter limp mode or refuse to energize high-voltage relays

What to check

  • Observe OEM safety procedures and remove HV system enable before any high-voltage work
  • Read freeze frame and live data with a capable scan tool; note status of Interlock G
  • Inspect harness and connectors for physical damage, corrosion, water, or contaminants
  • Visually inspect interlock switch/sensor mounting and associated hardware
  • Check for related DTCs in HV, BCM, BMS, and inverter modules
  • Verify connector pin integrity and proper terminal seating

Signal parameters

  • Expected normal (closed) interlock signal: near 0 V (or specified low voltage) to controller reference
  • Expected open/interlocked: near battery voltage (approx. 12 V) on some systems or a defined open-circuit voltage depending on design
  • Fault condition reported when signal > specified threshold (varies by manufacturer) — consult wiring diagram/service manual
  • Intermittent or fluctuating readings may indicate poor contact, corrosion, or broken conductor
  • Always confirm expected levels on the vehicle-specific wiring diagram before replacing components

Diagnostic algorithm

  1. Safety first: follow OEM high-voltage safety procedures. Disable HV system and wear required PPE before accessing HV wiring or connectors.
  2. Connect a diagnostic scan tool. Record U3528 freeze-frame data and any related codes. Note state of Interlock G and any associated status flags.
  3. Visually inspect the entire Interlock G circuit harness, connectors, and the interlock switch/sensor for damage, corrosion, water ingress or loose mounting.
  4. With HV disabled and vehicle low-voltage power per OEM instructions, perform continuity checks on the interlock wiring between the sensor/switch and the monitoring module. Check for opens, shorts to adjacent circuits, and unexpected continuity to battery positive.
  5. Check connector pins for proper seating, bent or pushed-out terminals, and damage. Repair or replace connectors as needed.
  6. Re-enable low-voltage power per manufacturer guidance (but keep HV disabled unless safe to do so). Measure the interlock signal voltage at the module input and at the interlock switch while operating any manual service interlocks (if safe to actuate). Compare to expected values from the wiring diagram.
  7. Wiggle-test the harness and connectors while monitoring live data/voltage to reproduce intermittent faults. Inspect for movement-related changes.
  8. If wiring and connectors are good, test or replace the interlock switch/sensor per service manual. Some modules may require removal/bench-testing of the sensor.
  9. If the sensor and wiring are good, check the monitoring module input circuit (or related control module) for faults. Consider module reflash or replacement only after wiring and sensor are confirmed good.
  10. After repairs, clear codes, attempt to recreate the fault with system cycling, and verify proper system operation and that the DTC does not return.
  11. If fault persists and diagnostics are inconclusive, consult vehicle-specific service data or contact technical support for manufacturer-specific test procedures.

Likely causes

  • Damaged insulation allowing short to vehicle 12 V
  • Connector pins pushed out, bent, or corroded producing a high voltage reading
  • Interlock switch contacts failed open internally and the signal is pulled to a high reference
  • Broken wire or chafed harness that creates intermittent high-voltage readings
  • Failed resistor or circuit element in the interlock assembly
  • Faulty module input stage incorrectly reporting a high value

Fault status

⚠️ Status
Interlock Circuit G voltage above expected threshold — HV interlock fault recorded. HV functions may be disabled until condition is resolved.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1.5-3 hours (varies by vehicle and access to connectors/sensors)

Similar codes

U3527 U3529 U0100 U0121 U0146
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