What are the common causes of U3523?

A short to ground on interlock loop F. High resistance in interlock loop F. A loose interlock loop F connector. Water bridging interlock loop F to ground.

Read high voltage interlock circuit F status on a scan tool. De-energize the high voltage system before touching any connector. Test interlock loop F for a short to ground. Inspect interlock loop F connector and wiring. Repair interlock loop F if the signal stays low. Clear the code and retest.

U3523

High Voltage System Interlock Circuit F Low

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

What it means

U3523 means High Voltage System Interlock Circuit F Low.

Check these first

A short to ground on interlock loop F
High resistance in interlock loop F
A loose interlock loop F connector
Water bridging interlock loop F to ground

What to do next

Read high voltage interlock circuit F status on a scan tool
De-energize the high voltage system before touching any connector
Test interlock loop F for a short to ground
Inspect interlock loop F connector and wiring
Repair interlock loop F if the signal stays low
Clear the code and retest

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Updated

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