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DTC codes / U35xx · Network communication / U3514

U3514High Voltage System Interlock Circuit B High

U3514 indicates that the high-voltage interlock loop for circuit B has reported a voltage above the expected threshold, which the vehicle's control module interprets as a potential safety breach. The interlock is a low-voltage safety circuit that runs through high-voltage connectors and components, and it is designed to disable the high-voltage system if any connection is broken or compromised. The computer detected an abnormally high voltage on this specific interlock circuit, which can trigger a shutdown of the high-voltage system to prevent electric shock hazards.

SystemNetwork
Code typeGeneric (all makes)
SeverityHigh
Fix difficultyProfessional
AreaNetwork communication

Symptoms you may notice

  • High-voltage system disabled, preventing the vehicle from starting or driving
  • Instrument cluster displays a high-voltage system fault or service vehicle soon message
  • Reduced power or limp mode if the vehicle remains drivable
  • Often no symptoms besides the warning light, especially if the fault is intermittent
  • Inability to charge the high-voltage battery on plug-in vehicles
  • Audible alerts or chimes accompanying the warning light

Common causes, most likely first

  1. Damaged or corroded high-voltage interlock connector pins or terminals
  2. Frayed, pinched, or open interlock wiring harness
  3. Failed high-voltage component (e.g., battery pack, inverter, motor) with internal interlock fault
  4. Water intrusion or contamination in a high-voltage connector
  5. Loose or improperly seated high-voltage connector
  6. Faulty interlock detection circuit within the control module
  7. Aftermarket accessories or improper previous repairs interfering with the interlock loop

How to diagnose and fix it

  1. Perform a visual inspection of all high-voltage connectors and wiring for damage, corrosion, or loose connections
  2. Use a scan tool to read all stored codes and freeze-frame data, and check for related codes in other modules
  3. Consult the factory service information for the specific interlock circuit B routing and test procedures
  4. Measure resistance and voltage on the interlock circuit B at the control module and at each connector, comparing to specifications
  5. Disconnect and reseat each high-voltage connector in the circuit, checking for proper terminal tension and cleanliness
  6. If a faulty component is identified, replace or repair it following manufacturer procedures, then clear codes and verify the repair
  7. If the fault persists, perform pinpoint tests on the control module and interlock circuit as directed by service information

Interlock faults are not always component failures

  • A common cause of U3514 is a partially disconnected high-voltage connector that still makes contact but has high resistance, which can set the code without any visible damage.
  • The interlock circuit is a low-voltage loop, so a high voltage reading on it often indicates a short to voltage rather than an open circuit, which changes the diagnostic approach.
  • Many technicians replace high-voltage components unnecessarily when the real problem is a chafed interlock wire behind a connector or under a harness cover.
  • After any high-voltage repair, the interlock circuit must be verified for continuity and correct voltage before the system will re-enable, and some vehicles require a specific reset procedure.
  • This code can be set by a low 12-volt battery or poor ground connection, causing the control module to misread interlock voltage, so always check the basics first.

Can I keep driving with U3514?

Do not continue driving with this code active, as the high-voltage system may be disabled or in a compromised state, and driving could risk electric shock or further damage. Have the vehicle towed to a qualified service facility for diagnosis and repair.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

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