What are the common causes of U3518?

A short to voltage on interlock loop C. An open in interlock loop C. A loose interlock loop C connector. A failed interlock monitor inside the module.

Read high voltage interlock circuit C status on a scan tool. De-energize the high voltage system before touching any connector. Test interlock loop C for a short to voltage and opens. Inspect interlock loop C connector pins and wiring. Repair interlock loop C or replace the interlock module if the signal stays high. Clear the code and retest.

U3518

High Voltage System Interlock Circuit C High

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

What it means

U3518 means High Voltage System Interlock Circuit C High.

Check these first

A short to voltage on interlock loop C
An open in interlock loop C
A loose interlock loop C connector
A failed interlock monitor inside the module

What to do next

Read high voltage interlock circuit C status on a scan tool
De-energize the high voltage system before touching any connector
Test interlock loop C for a short to voltage and opens
Inspect interlock loop C connector pins and wiring
Repair interlock loop C or replace the interlock module if the signal stays high
Clear the code and retest

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Updated

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