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Home / DTC / U3513 — High Voltage System Interlock Circuit B Low

U3513 — High Voltage System Interlock Circuit B Low

Detailed page for trouble code U3513.

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U3513

Generic U — Network/User

High Voltage System Interlock Circuit B Low

Brand: Generic
Type: U — Network/User
Views: UK: 17 EN: 26 RU: 19
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Page language: EN

Causes

  • Open, short-to-ground, or short-to-voltage in the interlock wiring harness
  • Corroded, bent, or poorly seated connector at an interlock switch or control module
  • Failed HV interlock switch (service disconnect, charge port latch, safety plug, etc.)
  • Blown fuse or faulty relay feeding the interlock circuit or its pull-up resistor
  • Faulty body/vehicle control module or HV battery management/control module input circuit
  • Water intrusion or physical damage to wiring or connectors

Symptoms

  • HV system disablement or inhibit (vehicle may refuse to enter ready/drive state)
  • HV warning lamp, MIL, or specific HV interlock warning displayed
  • Charging disabled or charge port locked
  • Reduced or no drive power in hybrid/electric vehicles
  • DTC stored; possible limp-home or service mode

What to check

  • Read and record freeze frame and live data with a capable scan tool; confirm U3513 and any related codes
  • Visual inspection of Interlock B switch, connectors, and harness for corrosion, damage, or water intrusion
  • Check fuses and relays related to the interlock sensing/pull-up circuit
  • Backprobe the interlock circuit at the control module and the switch connector to compare voltages
  • Perform continuity and resistance checks between the switch and module with ignition off (follow manufacturer HV safety procedures)
  • Wiggle harness/connectors while observing live data to reproduce the fault

Signal parameters

  • Typical expected states (manufacturer dependent): closed (interlock engaged) = low voltage (
  • Open-circuit (disconnected) usually shows high impedance or the pull-up voltage at the module input.
  • Short-to-ground will show very low resistance to chassis ground (
  • Short-to-battery/voltage will show near battery voltage at the input (~12 V) when ignition on (if design uses 12 V pull-up).
  • Expected continuity when switch closed: near 0 ohms across switch contacts; when open: infinite/very high ohms.

Diagnostic algorithm

  1. Safety first: follow manufacturer high-voltage safety procedures before working on HV components. Wear specified PPE and isolate the HV battery if required for the checks you will perform.
  2. Connect a scan tool, confirm U3513, note freeze frame and related codes, and monitor live data for Interlock B state while cycling the service disconnect/charge port/lid or other interlock devices.
  3. Visually inspect the interlock switch(es), connectors, and wiring for corrosion, damage, water entry, or loose pins. Repair or reseat connectors as needed.
  4. With ignition per manufacturer instructions, backprobe the interlock input at the switch and at the control module. Compare voltages to the expected pull-up and low states (see signal_params).
  5. Check fuses/relays and the presence of the pull-up voltage at the module input. Replace faulty fuses or relays.
  6. Perform continuity and resistance checks between the switch and the module input with power removed and HV system made safe. Repair any opens or shorts in the harness.
  7. If the switch shows correct operation and wiring continuity is good, swap or bench-test the interlock switch (if serviceable) or replace it.
  8. If wiring and switch are good, suspect the receiving control module input. Verify other inputs to that module and check for software updates or known module faults before replacing the module.
  9. After repairs, clear codes and road-test or cycle the interlock to confirm the fault does not return.

Likely causes

  • Connector corrosion or poor pin contact at Interlock B sensor/switch
  • Open or shorted harness between the interlock switch and the control module
  • Failed interlock switch (mechanical stuck/shorted)
  • Missing or blown fuse/pull-up resistor causing the input to read low
  • Module input fault (less common)

Fault status

⚠️ Status
High Voltage System Interlock Circuit B Low — input below expected threshold (possible closed switch, short to ground, open harness, or faulty module).
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 1.0-2.5 hours

Similar codes

U3512 U3514 U3501 U0100 P0A7F
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