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Home / DTC / U3512 — High Voltage System Interlock Circuit B Performance

U3512 — High Voltage System Interlock Circuit B Performance

Detailed page for trouble code U3512.

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Code

U3512

Generic U — Network/User

High Voltage System Interlock Circuit B Performance

Brand: Generic
Type: U — Network/User
Views: UK: 13 EN: 22 RU: 19
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Page language: EN

Causes

  • Open or short in the interlock harness (broken conductor, chafed insulation, pinched wire)
  • Corroded, loose or contaminated interlock connector or terminal
  • Faulty interlock switch/sensor (service plug, HV connector latch, charge inlet switch)
  • Water intrusion or dirt in interlock connectors or junctions
  • Poor ground or reference voltage to the interlock circuit
  • Intermittent connection due to damaged grommet or connector seating

Symptoms

  • HV system will not enable or vehicle will not power up for propulsion
  • HV disabled lamp, master warning, or specific HV interlock warning displayed
  • Inability to charge or charge session aborts
  • Reduced vehicle functionality or limp-home mode
  • DTC U3512 stored and may be accompanied by other HV interlock or BMS codes
  • Intermittent/noisy behavior when connectors are moved or vehicle is jostled

What to check

  • Read all stored and pending codes from HV/can modules; record freeze frame and related codes
  • Visually inspect interlock B harness routing, connectors, and service plugs for damage, contamination or water ingress
  • Confirm all HV interlocks (service plug, charging inlet, HV connector latches) are fully seated and latched
  • Perform wiggle test on suspect connectors while monitoring live interlock status with a scan tool (do this with appropriate HV precautions)
  • Measure continuity/resistance of the interlock loop with HV system de-energized (follow manufacturer safety procedures)
  • Check supply/reference voltage and ground for the interlock circuit at the module connector with ignition/state as required by service manual

Signal parameters

  • Interlock continuity (loop closed): typically very low resistance — often < 1–10 ohms (consult service manual for exact spec)
  • Interlock open condition: very high resistance or infinite (open circuit) — typically > 100 kΩ
  • Control/reference voltage: some interlock circuits use 5 V logic or battery/ignition reference (approx. 5 V or 12 V) — verify exact nominal with service documentation
  • Logical signal states reported to module: CLOSED/OK vs OPEN/FAULT or specific voltage thresholds defined by manufacturer
  • If monitoring analog voltage, nominal fault-free voltage should match service data; deviation or intermittent swings indicate wiring/sensor issues

Diagnostic algorithm

  1. Safety first: follow manufacturer high-voltage safety procedures. Disable HV system and remove service/interlock plugs as required before probing harnesses.
  2. Connect a capable OEM-level scan tool. Read and record U3512 and any other related codes and live data (interlock B status, voltages). Clear codes to see if fault returns.
  3. Visually inspect connectors, harness, service plug and charge inlet for corrosion, damage, unseated connectors, or moisture. Repair obvious damage.
  4. With HV system safely de-energized and vehicle in a safe state for continuity checks, measure resistance/continuity of interlock loop B between module connector pins and the actual interlock switch/device. Compare to expected values.
  5. Inspect and probe connector terminals for corrosion/loose pins. Backprobe connector at control module to verify continuity to interlock device and to check reference/ground presence per service data.
  6. Re-energize system only when safe and required by procedure. Monitor live interlock signals while operating the interlock (plug/unplug, latch/unlatch, actuate switch). Perform wiggle test to detect intermittent faults.
  7. If wiring and connectors are good, test/replace the interlock switch or service plug assembly and retest.
  8. If fault persists after replacing switch and repairing wiring, suspect input circuit fault in control module (BCM/BMS). Verify with manufacturer diagnostics; do not replace module without conclusive evidence.
  9. After repairs, clear codes, perform full system enable/charge sequence and a road/charge test to confirm the fault does not return. Re-scan for related codes.

Likely causes

  • Poor connector contact or corrosion at the interlock harness/connector
  • Open or intermittent wiring in the interlock loop B harness (pin damage, chafe, broken wire)
  • Faulty interlock switch (service plug, HV connector latch or charge inlet sensor)
  • Moisture ingress in connector or service plug area
  • Module input circuit fault or ground issue (less common than wiring/switch faults)

Fault status

⚠️ Status
U3512 – High Voltage System Interlock Circuit B Performance: Interlock loop B reporting out-of-range or intermittent signal. HV enable/charge may be disabled. Inspect interlock harness, connectors, and switch.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1.0-3.0 hours

Similar codes

U3500 U3501 U3511 U3513 U3570 P1A00
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