01 Unveiling the 10 Cars That Cost More to Run Than to Buy • 02 Drivers Left Shocked After Realizing What Black Smoke From … • 03 P0106: Manifold Absolute Pressure (MAP) System Performance • 04 Engine Block Cleaning: A Step-by-Step Guide for Optimal Per… • 05 CVT Gearbox Blues: Common Problems and Warning Signs • 06 The Gearbox Technology That Makes Every Driver's Car Unique… • 07 The Business of Car Importation: Profits and Risks Explained • 08 Charging Anxiety vs. Green Future: Why Americans Aren't Buy… • 09 Why are Catalytic Converters Stolen and How to Prevent It • 10 Oil filter vs. oil: Which is more important to change? •

DTC codes / U35xx · Network communication / U351D

U351DHigh Voltage System Interlock Circuit E

U351D indicates that the high-voltage interlock loop, a safety circuit that confirms all high-voltage connectors and covers are properly seated, has detected a fault in circuit E. The vehicle's control module monitors a low-voltage signal through the interlock chain and sets this code when the voltage on that specific segment is higher than expected, which typically means the loop is broken or a connector is not fully engaged.

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

Symptoms you may notice

  • High-voltage system warning light or message on the dashboard
  • Vehicle may refuse to start or enter 'ready' mode
  • Reduced power or limp mode, often limiting speed
  • High-voltage components such as the air conditioning compressor or cabin heater may stop working
  • Often no symptoms besides the warning light, especially if the fault is intermittent
  • Charging system may be disabled on plug-in vehicles

Common causes, most likely first

  1. A high-voltage connector that is not fully latched or has a damaged interlock pin
  2. Corrosion or water intrusion in a high-voltage connector or junction box
  3. A broken or chafed interlock wire in the harness between high-voltage components
  4. A faulty high-voltage component with an internal interlock switch (e.g., battery pack, inverter, charger)
  5. A malfunctioning high-voltage control module or interlock detection circuit
  6. Aftermarket or improper repair that bypassed or damaged the interlock loop
  7. Loose or damaged service disconnect plug or manual disconnect switch

How to diagnose and fix it

  1. Inspect all high-voltage connectors for proper seating and latch engagement, especially those recently disturbed
  2. Check for corrosion, moisture, or bent pins in the interlock circuit connectors
  3. Perform a voltage drop or continuity test on the interlock loop segment E using the manufacturer's wiring diagram
  4. Scan all modules for related codes and freeze-frame data to identify which component reported the fault
  5. Isolate the fault by disconnecting high-voltage components one at a time and monitoring the interlock signal
  6. Repair or replace damaged wiring, connectors, or the faulty high-voltage component as needed
  7. Clear codes and verify the interlock circuit operates correctly under all conditions

Interlock faults are often simple connector issues

  • A high-voltage interlock loop is a low-voltage safety circuit, so a U351D does not necessarily mean the high-voltage system itself has a dangerous fault.
  • Many interlock codes are set after routine service when a high-voltage connector is not fully clicked into place, so always check recent work first.
  • The code refers to 'Circuit E', which is one segment of the overall interlock loop; the fault may be in a connector or component that seems unrelated to the main battery.
  • Some vehicles set an interlock code when the 12-volt battery is weak or disconnected, causing a false trigger that clears after proper reset.
  • Never bypass or jumper an interlock circuit to 'fix' a no-start condition; it defeats a critical safety system and can lead to serious injury.

Can I keep driving with U351D?

Do not drive the vehicle with an active U351D code, because the high-voltage system may be disabled or in a fail-safe mode that affects power and charging. Have the vehicle inspected by a qualified high-voltage technician before attempting to move it under its own power.

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.

Running on fumes Free guides aren't free to make. Top up the tank. Any amount, one time. Fuel the Garage