Damaged or corroded interlock connector pins or terminals in circuit D; Frayed or broken interlock wire causing an open circuit that raises loop voltage; Failed high-voltage interlock switch inside a connector or service disconnect; Water intrusion or contamination in a high-voltage connector causing high resistance; Faulty control module or interlock detection circuit internal error; Aftermarket accessories or improper previous repairs tapping into the interlock loop; Loose or improperly seated high-voltage connector after service

DTC codes / U35xx · Network communication / U3519

U3519High Voltage System Interlock Circuit D

Q: What does code U3519 mean?

High Voltage System Interlock Circuit D. U3519 indicates that the high-voltage interlock loop circuit D has reported a voltage above the expected range, which the vehicle's control module interprets as a potential safety breach. The interlock is a low-voltage safety loop that runs through high-voltage connectors and covers; when its voltage is too high, the system may disable the high-voltage contactors to prevent shock hazard.

U3519 indicates that the high-voltage interlock loop circuit D has reported a voltage above the expected range, which the vehicle's control module interprets as a potential safety breach. The interlock is a low-voltage safety loop that runs through high-voltage connectors and covers; when its voltage is too high, the system may disable the high-voltage contactors to prevent shock hazard.

SystemNetwork

Code typeGeneric (all makes)

SeverityHigh

Fix difficultyProfessional

AreaNetwork communication

Symptoms you may notice

High-voltage system warning light or message on the dashboard
Vehicle may refuse to start or enter 'ready' mode
Reduced power or limp mode if the vehicle is already running
High-voltage battery contactors may open, cutting power to the drive motor
Often no symptoms besides the warning light if the fault is intermittent
Charging system may be disabled or refuse to initiate a charge session

Common causes, most likely first

Damaged or corroded interlock connector pins or terminals in circuit D
Frayed or broken interlock wire causing an open circuit that raises loop voltage
Failed high-voltage interlock switch inside a connector or service disconnect
Water intrusion or contamination in a high-voltage connector causing high resistance
Faulty control module or interlock detection circuit internal error
Aftermarket accessories or improper previous repairs tapping into the interlock loop
Loose or improperly seated high-voltage connector after service

How to diagnose and fix it

Inspect all high-voltage connectors and service disconnects for proper seating, corrosion, or damage
Check interlock loop continuity and resistance with a multimeter according to service information
Verify battery voltage and ground integrity at the control module that monitors the interlock
Scan all modules for related codes and freeze-frame data to identify which circuit D component triggered the fault
Perform a wiggle test on interlock wiring and connectors while monitoring live data to catch intermittent faults
Repair or replace damaged interlock wiring, pins, or connectors using approved high-voltage safe procedures
Clear codes and perform a road test to confirm the repair, ensuring the high-voltage system re-enables

Interlock faults are rarely the module itself

A high voltage reading on the interlock loop often results from a poor connection rather than a failed component, so inspect connectors before condemning parts.
The interlock circuit is a safety loop, not a power circuit; a voltage above range usually means the loop is open or has excessive resistance somewhere along its path.
Water damage or corrosion inside a high-voltage connector can raise interlock voltage without any visible external damage, so disassemble and inspect internally.
After any high-voltage service, a partially latched connector can set U3519 even though the vehicle seems to drive normally, so always verify full engagement.
Some vehicles set U3519 as a companion code when the 12-volt battery is weak or charging system voltage is abnormal, so check the low-voltage system first.

Can I keep driving with U3519?

Do not continue driving with U3519 active because the high-voltage system may shut down unexpectedly or remain disabled, increasing the risk of a crash or shock hazard. Have the vehicle inspected by a qualified high-voltage technician before attempting further operation.

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.