U351E

Code

Generic U — Network/User

High Voltage System Interlock Circuit E Performance

Brand: Generic

Type: U — Network/User

Views: UK: 19 EN: 30 RU: 19

AI status

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Page language: EN

Causes

Damaged or corroded connectors in the high-voltage interlock loop
Open, shorted or high-resistance wiring in the interlock circuit
Faulty interlock switch, sensor, or loop monitoring module
Poor ground or supply to the monitoring circuit
Intermittent connector contact due to vibration or improper seating
Software/firmware bug or communication error in the managing ECU (less common)

Symptoms

HV system disabled or unable to enable (vehicle won’t enter READY state)
HV-related warning lights or message (e.g., HV system fault, service required)
Reduced drive power or limp mode
Intermittent loss of HV enablement or random shut-down of HV functions
DTC U351E stored, possibly with related codes

What to check

Obtain and record freeze-frame and related codes using a capable scan tool; check for other HV or communication codes
Visually inspect interlock circuit routing: connectors, service disconnects, charge inlet, and battery access plugs for corrosion, damage or looseness
Confirm correct torquing/seating of removable HV interlocks (service plugs) and inspect for intrusion of debris
Inspect fuses and relays related to the interlock monitor/supply circuit
Using appropriate safety procedures for HV systems, check continuity and resistance of the interlock loop at serviceable points (with HV isolated/)
Check connector pins for damage, corrosion or bent terminals and verify secure locking

Signal parameters

Interlock circuit is typically a closed/open loop monitored by the module — expected: closed (low resistance) when assembled, open (high/OL) when service plug removed
Monitoring circuit will report discrete state (Open/Closed) or a DC voltage near 0 V or battery-supply voltage depending on design — compare to factory wiring diagram and live-data values
Continuity: low ohms across closed interlock contacts; infinite/OL when open. Excessive resistance (hundreds of ohms) indicates a problem
CAN/UH communication: interlock status bits should update when physical interlock is changed; absence of updates indicates wiring/module/communication issue

Diagnostic algorithm

Safety first: follow vehicle manufacturer HV isolation and PPE procedures before touching any high-voltage components.
Connect a factory-level or equivalent scan tool; read and record U351E and any related codes and freeze-frame data.
Inspect visible interlock components and connectors (service plug, charge inlet interlock, battery disconnects). Repair or reseat any corrosion/loose connectors.
Clear the code and attempt to reproduce while monitoring live-data interlock status. Note whether the DTC returns and under what conditions.
With HV isolated as required, perform continuity and resistance checks of the interlock loop at serviceable points. Compare measured values to the expected (closed ≈ low ohms; open ≈ OL).
If continuity is abnormal, isolate the section with the fault by disconnecting segments and repeating checks to locate the open/high-resistance area.
Inspect and test power and ground feeds to the interlock monitoring module, including related fuses and relays.
If wiring and connectors check good, swap or bench-test the interlock switch/module if a known-good component is available or follow manufacturer guidance for module testing.
If fault is intermittent, perform vibration/wiggle tests on harnesses and connectors while monitoring live data to find intermittent contact.
After repair, clear codes, perform full system enable sequence, and verify the interlock reports correct states and that the HV system enables normally.
If unable to isolate, consult OEM wiring diagrams, interlock loop schematics, and technical service bulletins; escalate to manufacturer-level diagnostics as required.

Likely causes

Corroded/loose interlock connector at a service plug, charge inlet, or battery disconnect
Broken conductor or chafed wiring in harness where it flexes
High-resistance connection at interlock switch or contacting surfaces
Failed interlock switch or loop monitor module
Blown fuse or tripped relay supplying the interlock monitor

Fault status

⚠️ Status

High-voltage interlock circuit E is outside expected performance (open, short, high resistance, or failing to report state). The control module may disable the HV system until the circuit is repaired or validated.

🔴 Repair difficulty: Hard

⏱️ Diagnostic time: 1.5-4.0 hours

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