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U3513 — High Voltage System Interlock Circuit B Low

Manufacturer-specificNetwork / communication

U3513 indicates a low voltage condition on the high voltage system interlock circuit B in hybrid/electric vehicles. This circuit monitors the integrity of high voltage connections; a low reading typically means a break, poor connection, or component fault that compromises safety. The vehicle may disable high voltage systems to prevent electrical hazards.

Symptoms

What causes it — most likely first

1. Faulty high voltage interlock switch or connector

The most common cause is a defective service disconnect switch, battery pack connector, or other interlock component that fails to close the circuit properly.

2. Open or short in interlock wiring

Chafed, broken, or corroded wires in the interlock circuit B can cause a low voltage reading. This often occurs near high voltage components or in harness routing areas.

3. Corroded or loose terminals

Corrosion at connector terminals or loose pin fit can create high resistance, leading to a low voltage condition on the interlock circuit.

4. Faulty high voltage component (inverter, converter, or battery module)

An internal failure in a high voltage component (e.g., inverter, DC-DC converter, or battery module) can cause the interlock circuit to read low.

5. Faulty battery management system (BMS) module

Less commonly, a BMS module that monitors the interlock circuit may malfunction and report a false low voltage.

6. Powertrain control module (PCM/ECM) failure

Extremely rare; the PCM/ECM is almost never the cause of U3513. Only consider after all other possibilities are exhausted and verified.

How it's diagnosed

  1. Perform a visual inspection of all high voltage interlock components, including the service disconnect, battery pack connectors, and inverter/converter connectors, looking for damage, corrosion, or loose fit.
  2. Using a digital multimeter (with proper high voltage safety precautions), measure the voltage on interlock circuit B at the PCM/ECM connector and compare to manufacturer specifications.
  3. Check continuity of the interlock circuit B wiring from the PCM/ECM to each interlock switch and component. Look for opens or shorts to ground.
  4. Inspect and clean all interlock circuit terminals; apply dielectric grease if specified by the manufacturer.
  5. Use a scan tool to monitor the interlock circuit B voltage live data while manually operating interlock switches (e.g., service disconnect) to isolate the fault.
  6. If all wiring and connectors test good, test or swap the suspected high voltage component (e.g., inverter) with a known-good unit, then re-evaluate.

Code facts & related codes

SystemNetwork / communication
StandardizationManufacturer-specific (P1/B1/C1/U1)
Related codesU3510 — Control Module Missing CalibrationU3511 — High Voltage System Interlock Circuit U3512 — High Voltage System Interlock Circuit U3514 — High Voltage System Interlock Circuit U3515 — High Voltage System Interlock Circuit U3516 — High Voltage System Interlock Circuit

Frequently asked

Can I drive the vehicle with code U3513?

No. This code indicates a safety interlock fault in the high voltage system. The vehicle may disable high voltage power, and driving could be unsafe or cause further damage. Have the vehicle towed to a qualified repair facility.

Is it safe to work on the high voltage system myself?

No. High voltage systems can cause severe injury or death. Only trained professionals with proper safety equipment and knowledge should diagnose or repair this code.

Do I need to replace the PCM/ECM for U3513?

Almost never. The PCM/ECM is rarely the cause of this code. Most cases are due to faulty interlock switches, connectors, wiring, or high voltage components. Replacing the PCM without proper diagnosis is a common and costly mistake.

How much does it typically cost to fix U3513?

Repair costs vary widely depending on the root cause, vehicle make, and labor rates. A simple connector repair may be inexpensive, while replacing a high voltage component can be costly. A proper diagnosis is essential before any repair.