Fault Family System: Network (U-Codes) 56 SAE Codes

HV Interlock Circuit Fault

Diagnostic & Technical Explanation

U3511 indicates the high-voltage interlock loop -- a low-voltage sense circuit daisy-chained through every high-voltage connector, service disconnect, and cover on a hybrid or EV powertrain -- has opened, so the vehicle's safety logic assumes a high-voltage connection may be exposed and disables the drive system. This is a physical continuity fault through a chain of small interlock pins, not a communication-bus problem, and the most common cause is a high-voltage connector or service panel that was not fully latched during prior service. Only qualified technicians with insulated PPE should work beyond the interlock loop, since the chain protects access to lethal DC voltage.

These 56 diagnostic trouble codes share one detection mechanism and one repair path, which is why MechanicDB groups them into a single authored fault family rather than repeating the same explanation 56 times.

Codes in this family (56)

Code	Definition	Repair coverage
U3511	High Voltage System Interlock Circuit B	4 ranked fixes
U3512	High Voltage System Interlock Circuit B Performance	4 ranked fixes
U3513	High Voltage System Interlock Circuit B Low	4 ranked fixes
U3514	High Voltage System Interlock Circuit B High	4 ranked fixes
U3515	High Voltage System Interlock Circuit C	4 ranked fixes
U3516	High Voltage System Interlock Circuit C Performance	4 ranked fixes
U3517	High Voltage System Interlock Circuit C Low	4 ranked fixes
U3518	High Voltage System Interlock Circuit C High	4 ranked fixes
U3519	High Voltage System Interlock Circuit D	4 ranked fixes
U351A	High Voltage System Interlock Circuit D Performance	4 ranked fixes
U351B	High Voltage System Interlock Circuit D Low	4 ranked fixes
U351C	High Voltage System Interlock Circuit D High	4 ranked fixes
U351D	High Voltage System Interlock Circuit E	4 ranked fixes
U351E	High Voltage System Interlock Circuit E Performance	4 ranked fixes
U351F	High Voltage System Interlock Circuit E Low	4 ranked fixes
U3520	High Voltage System Interlock Circuit E High	4 ranked fixes
U3521	High Voltage System Interlock Circuit F	4 ranked fixes
U3522	High Voltage System Interlock Circuit F Performance	4 ranked fixes
U3523	High Voltage System Interlock Circuit F Low	4 ranked fixes
U3524	High Voltage System Interlock Circuit F High	4 ranked fixes
U3525	High Voltage System Interlock Circuit G	4 ranked fixes
U3526	High Voltage System Interlock Circuit G Performance	4 ranked fixes
U3527	High Voltage System Interlock Circuit G Low	4 ranked fixes
U3528	High Voltage System Interlock Circuit G High	4 ranked fixes
U3529	High Voltage System Interlock Circuit H	4 ranked fixes
U352A	High Voltage System Interlock Circuit H Performance	4 ranked fixes
U352B	High Voltage System Interlock Circuit H Low	4 ranked fixes
U352C	High Voltage System Interlock Circuit H High	4 ranked fixes
U352D	High Voltage System Interlock Circuit J	4 ranked fixes
U352E	High Voltage System Interlock Circuit J Performance	4 ranked fixes
U352F	High Voltage System Interlock Circuit J Low	4 ranked fixes
U3530	High Voltage System Interlock Circuit J High	4 ranked fixes
U3531	High Voltage System Interlock Circuit K	4 ranked fixes
U3532	High Voltage System Interlock Circuit K Performance	4 ranked fixes
U3533	High Voltage System Interlock Circuit K Low	4 ranked fixes
U3534	High Voltage System Interlock Circuit K High	4 ranked fixes
U3535	High Voltage System Interlock Circuit L	4 ranked fixes
U3536	High Voltage System Interlock Circuit L Performance	4 ranked fixes
U3537	High Voltage System Interlock Circuit L Low	4 ranked fixes
U3538	High Voltage System Interlock Circuit L High	4 ranked fixes
U3539	High Voltage System Interlock Circuit M	4 ranked fixes
U353A	High Voltage System Interlock Circuit M Performance	4 ranked fixes
U353B	High Voltage System Interlock Circuit M Low	4 ranked fixes
U353C	High Voltage System Interlock Circuit M High	4 ranked fixes
U353D	High Voltage System Interlock Circuit N	4 ranked fixes
U353E	High Voltage System Interlock Circuit N Performance	4 ranked fixes
U353F	High Voltage System Interlock Circuit N Low	4 ranked fixes
U3540	High Voltage System Interlock Circuit N High	4 ranked fixes
U3541	High Voltage System Interlock Circuit O	4 ranked fixes
U3542	High Voltage System Interlock Circuit O Performance	4 ranked fixes
U3543	High Voltage System Interlock Circuit O Low	4 ranked fixes
U3544	High Voltage System Interlock Circuit O High	4 ranked fixes
U3545	High Voltage System Interlock Circuit P	4 ranked fixes
U3546	High Voltage System Interlock Circuit P Performance	4 ranked fixes
U3547	High Voltage System Interlock Circuit P Low	4 ranked fixes
U3548	High Voltage System Interlock Circuit P High	4 ranked fixes

What this page does not show

This page publishes the fault mechanism and the code index. The licensed dataset adds, for every one of the 15,886 codes, the full authored repair set (56,729 procedures in total) with the fields deliberately withheld here:

Procedures 2..n after the first-listed procedure
Aftermarket parts cost ranges in USD (est_parts_cost_min/max_usd)
Professional labor-hour estimates (est_labor_hours)
Step-by-step diagnostic and repair instructions
Replacement-part mappings and catalog lookups
6,637 manufacturer-specific OEM codes across 32 makes ($149 tier)

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