Loose, corroded, or unseated high-voltage connector on the interlock circuit B path; Damaged interlock wire (open or shorted to voltage) between the battery pack and a high-voltage component; Failed high-voltage interlock switch inside a connector or service disconnect plug; Water intrusion or contamination in a high-voltage connector causing abnormal voltage on the interlock loop; Faulty battery energy control module (BECM) or interlock monitoring circuit; Aftermarket or improper repair that bypassed or altered the interlock circuit; Pinched or chafed interlock harness near a high-voltage cable routing point

DTC codes / U35xx · Network communication / U3511

U3511High Voltage System Interlock Circuit B

Q: What does code U3511 mean?

High Voltage System Interlock Circuit B. U3511 indicates that the high-voltage interlock loop circuit B has reported a voltage above the expected range, which the battery energy control module interprets as a break or fault in the safety interlock path. The interlock is a low-current loop that runs through high-voltage connectors and covers, and the module monitors its voltage to confirm that all high-voltage connections are secure before allowing the contactors to close.

U3511 indicates that the high-voltage interlock loop circuit B has reported a voltage above the expected range, which the battery energy control module interprets as a break or fault in the safety interlock path. The interlock is a low-current loop that runs through high-voltage connectors and covers, and the module monitors its voltage to confirm that all high-voltage connections are secure before allowing the contactors to close.

SystemNetwork

Code typeGeneric (all makes)

SeverityHigh

Fix difficultyProfessional

AreaNetwork communication

Symptoms you may notice

Illuminated high-voltage system warning light or service vehicle soon message
Vehicle may refuse to start or enter 'ready' mode, leaving you with a no-start condition
Reduced power or limp-home mode if the vehicle does drive
High-voltage system may be disabled entirely, preventing charging on plug-in models
Often no symptoms besides the warning light if the fault is intermittent
Audible click or no click from the battery contactors when attempting to start

Common causes, most likely first

Loose, corroded, or unseated high-voltage connector on the interlock circuit B path
Damaged interlock wire (open or shorted to voltage) between the battery pack and a high-voltage component
Failed high-voltage interlock switch inside a connector or service disconnect plug
Water intrusion or contamination in a high-voltage connector causing abnormal voltage on the interlock loop
Faulty battery energy control module (BECM) or interlock monitoring circuit
Aftermarket or improper repair that bypassed or altered the interlock circuit
Pinched or chafed interlock harness near a high-voltage cable routing point

How to diagnose and fix it

Scan all modules for related codes and record freeze-frame data to understand when the fault sets
Inspect every high-voltage connector on circuit B for proper seating, corrosion, and water intrusion
Check the service disconnect plug and interlock switch for continuity and correct engagement
Measure interlock loop voltage and resistance at the BECM connector and compare to manufacturer specifications
Perform a wiggle test on the interlock harness while monitoring live data to catch intermittent faults
Repair or replace damaged interlock wiring, terminals, or connectors using high-voltage-rated components
If the circuit tests good, follow the diagnostic flow for BECM internal fault before replacing the module

Interlock faults that fool good technicians

A perfectly good high-voltage connector can still set U3511 if the small interlock pin inside it is bent or pushed back, so visual inspection of the main terminals is not enough.
The interlock loop often carries a low-voltage signal, so a short to voltage from a nearby 12-volt circuit can mimic an open circuit and send you chasing the wrong harness.
After any high-voltage repair, the interlock circuit must be fully seated and latched; a connector that clicks but is not fully engaged can set this code intermittently.
Some vehicles set U3511 when the 12-volt battery is weak because the BECM misreads the interlock voltage during low-voltage conditions, so always verify battery health first.
This code does not always mean the high-voltage battery is faulty; the fault is usually in the low-voltage interlock path, not the pack itself.

Can I keep driving with U3511?

Do not continue driving with U3511 active because the high-voltage system may be disabled or in a reduced-power state, and an interlock fault can prevent the contactors from closing safely. Have the vehicle inspected by a qualified high-voltage technician before attempting further use.

Tools that help

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Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.