What are the common causes of U3539?

An open in interlock loop M. A loose or corroded interlock loop M connector. High resistance in interlock loop M. Water in the interlock loop M connector.

Read high voltage interlock circuit M status on a scan tool. De-energize the high voltage system before touching any connector. Test interlock loop M for continuity and opens. Inspect interlock loop M connector and wiring. Repair interlock loop M if the circuit tests faulty. Clear the code and retest.

U3539

High Voltage System Interlock Circuit M

System: Network communication (U code)
Lamp: Check Engine Light
Category: Network Communications

What it means

U3539 means High Voltage System Interlock Circuit M.

Check these first

An open in interlock loop M
A loose or corroded interlock loop M connector
High resistance in interlock loop M
Water in the interlock loop M connector

What to do next

Read high voltage interlock circuit M status on a scan tool
De-energize the high voltage system before touching any connector
Test interlock loop M for continuity and opens
Inspect interlock loop M connector and wiring
Repair interlock loop M if the circuit tests faulty
Clear the code and retest

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Updated

Generic SAE J2012 definition. Last updated 2026-10-10.