U351D

Code

Generic U — Network/User

High Voltage System Interlock Circuit E

Brand: Generic

Type: U — Network/User

Views: UK: 26 EN: 34 RU: 22

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Page language: EN

Causes

Open or short in the HV interlock E wiring harness
Corroded, bent or loose interlock connector pins or connector not fully seated
Failed interlock switch or sensor (service plug, connector latch, charge inlet switch)
Water intrusion or contamination at connector or interlock device
Blown fuse, faulty relay, or poor ground affecting the interlock circuit power or reference
Control module input fault or internal module software/hardware error

Symptoms

HV system disabled or vehicle will not enter ready/drive mode
Reduced power or limp-home mode
Charging disabled or charge port fault
HV system or fault indicator lamps illuminated (HV/Service/Check EV System)
Possible stored or active U351D code visible with a scan tool

What to check

Read and record DTC(s) and freeze-frame data with a compatible scan tool; note key state and HV system status
Verify vehicle is made safe: follow manufacturer HV isolation procedures and wear appropriate PPE before touching HV components
Visual inspection of interlock E connector, harness, service disconnect, and associated components for damage, corrosion, moisture, or loose pins
Inspect related fuses, relays and ground points for continuity and proper seating
Check for other related DTCs (charging, HV battery, contactor, body harness) that may point to the root cause
If permitted, perform functional test of the interlock (operate connector latch/service plug) while monitoring the interlock input with a scan tool

Signal parameters

Typical continuity when interlock closed: low resistance (10 kΩ or OL).
Typical voltage behavior (varies by vehicle): interlock input pulled-up to battery/ignition voltage when open (~12 V) and pulled near 0 V when closed, or may be a 0/5 V logic signal depending on design — consult vehicle wiring diagram.
Intermittent/wiggle faults may produce changing resistance or voltage values when harness is moved.
If signal is shorted to ground: near 0 V with low resistance to chassis ground. If shorted to power: near battery voltage with low resistance to battery positive.

Diagnostic algorithm

Read all HV and body network codes; capture freeze-frame and pending codes. Do not assume U351D is the only symptom.
Follow OEM HV safety procedures. Disable HV system or remove service disconnect as required before accessing connectors.
Visually inspect the interlock E connector, adjacent harness, service plug and charge inlet for contamination, damage, or disconnected connectors. Repair obvious damage.
With the vehicle in a safe, isolated state and only if allowed by vehicle procedure, measure continuity of the interlock circuit between the interlock device terminal and the control module input pin. Expect near-zero ohms when closed; open when disengaged.
With power applied and using a scan tool, monitor the interlock input/status while operating the interlock device (engage/disengage service plug, latch, or inlet). Observe voltage/resistance transitions and note abnormalities or delays.
Check for water intrusion or corrosion and dry/clean connectors. Repair or replace corroded connectors or pigtails.
Repair damaged wiring (splice or replace harness section) and replace faulty interlock switch or connector as needed. Use OEM parts and correct sealing methods for HV environments.
Verify related fuses/relays and ensure proper ground continuity. Replace any defective components.
Clear codes and perform a functional test: re-initialize HV system per OEM procedure, attempt to charge/start and confirm code does not return and HV system operates normally.
If the circuit tests good and the code returns, consider module input fault — consult manufacturer service information for module bench test or replacement guidance.