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DTC codes / U35xx · Network communication / U351F

U351FHigh Voltage System Interlock Circuit E Low

U351F indicates that the high-voltage interlock loop for circuit E has reported a low voltage condition, meaning the safety monitoring circuit is not seeing the expected voltage level. The computer detects this when the interlock signal voltage falls below the manufacturer's specified threshold, which typically occurs when the loop is broken or a component is not properly seated.

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

Symptoms you may notice

  • Illumination of the high-voltage system warning light or service vehicle soon message
  • The vehicle may refuse to start or enter 'ready' mode, especially in electric and hybrid models
  • Reduced power or limp mode, limiting vehicle speed and acceleration
  • Often no symptoms besides the warning light, with the vehicle operating normally
  • Inability to engage the high-voltage system after a charging session or service procedure

Common causes, most likely first

  1. A high-voltage interlock connector that is not fully seated or has a broken latch
  2. Corrosion or water intrusion in an interlock connector or component housing
  3. Damaged wiring in the interlock loop, such as a chafed or broken wire
  4. A faulty high-voltage component (e.g., battery pack, inverter, or motor) with an internal interlock switch failure
  5. Improperly performed service work that left an interlock circuit disconnected
  6. A failed interlock detection circuit within the battery management or vehicle control module

How to diagnose and fix it

  1. Inspect all high-voltage interlock connectors for proper seating, latch engagement, and corrosion; reseat any loose connectors
  2. Check the interlock loop wiring for continuity and damage, repairing any open or shorted circuits
  3. Verify the interlock signal voltage at the module connector using a multimeter and compare to specifications
  4. Test individual high-voltage components for internal interlock continuity, isolating the faulty component
  5. Replace any faulty high-voltage component or interlock switch as required
  6. Clear the diagnostic trouble codes and perform a road test to confirm the repair
  7. If the fault persists, diagnose the interlock detection circuit in the control module and repair or replace as needed

Interlock Circuit E Low-Voltage Traps

  • A common oversight is assuming the interlock loop is broken when the actual problem is a low-voltage signal caused by a poor ground or a weak connection at the control module.
  • The interlock circuit is a safety loop, not a high-voltage power circuit, so a low voltage reading does not necessarily indicate a high-voltage component failure.
  • After any service that involves disconnecting high-voltage components, the interlock connectors must be fully latched; a partially seated connector can set this code without any visible damage.
  • Some vehicles set U351F when the 12-volt battery is weak or during low-voltage conditions, so always verify the 12-volt system before diving into high-voltage diagnostics.
  • The code may be stored alongside other interlock codes (e.g., U351A, U351B) if multiple circuits are affected, but U351F specifically points to circuit E.

Can I keep driving with U351F?

Do not continue driving with this code present, as the high-voltage system may be disabled or in a reduced-power mode, and safety systems could be compromised. Have the vehicle inspected by a qualified high-voltage technician before further use.

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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