Damaged or disconnected high-voltage interlock wiring or connector; Faulty high-voltage interlock switch inside a component (e.g., service disconnect, battery pack, inverter); Corrosion or water intrusion in a high-voltage connector; Loose or improperly seated high-voltage connector; Failed high-voltage control module or interlock detection circuit; Aftermarket accessories or improper previous repairs affecting the interlock loop

DTC codes / U35xx · Network communication / U3517

U3517High Voltage System Interlock Circuit C Low

Q: What does code U3517 mean?

High Voltage System Interlock Circuit C Low. U3517 is a manufacturer-specific code indicating that the high-voltage interlock loop for circuit C is reporting a low voltage condition, which the vehicle's control module interprets as a potential breach in the high-voltage safety circuit. The computer detects this when the interlock circuit's voltage falls below the expected threshold, often due to a broken connection, faulty switch, or damaged wiring in the high-voltage system.

U3517 is a manufacturer-specific code indicating that the high-voltage interlock loop for circuit C is reporting a low voltage condition, which the vehicle's control module interprets as a potential breach in the high-voltage safety circuit. The computer detects this when the interlock circuit's voltage falls below the expected threshold, often due to a broken connection, faulty switch, or damaged wiring in the high-voltage system.

SystemNetwork

Code typeGeneric (all makes)

SeverityHigh

Fix difficultyProfessional

AreaNetwork communication

Symptoms you may notice

High-voltage system warning light illuminated on the dashboard
Vehicle may refuse to start or enter 'ready' mode
Reduced power or limp mode due to high-voltage system shutdown
Often no symptoms besides the warning light if the interlock circuit is only intermittently low
Possible inability to charge the high-voltage battery (in plug-in vehicles)
Other high-voltage related codes stored in multiple modules

Common causes, most likely first

Damaged or disconnected high-voltage interlock wiring or connector
Faulty high-voltage interlock switch inside a component (e.g., service disconnect, battery pack, inverter)
Corrosion or water intrusion in a high-voltage connector
Loose or improperly seated high-voltage connector
Failed high-voltage control module or interlock detection circuit
Aftermarket accessories or improper previous repairs affecting the interlock loop

How to diagnose and fix it

Perform a visual inspection of all high-voltage connectors and wiring for damage, corrosion, or loose connections
Check service disconnect plug for proper seating and integrity
Use a scan tool to monitor interlock circuit voltage and identify which component is reporting the low signal
Perform continuity and resistance tests on the interlock circuit according to manufacturer procedures
Inspect and test individual high-voltage components (battery pack, inverter, motor) for internal interlock switch faults
Repair or replace damaged wiring, connectors, or faulty components as needed
Clear codes and verify the repair by test-driving and rechecking for return of the code

Interlock Circuit Low Voltage Pitfalls

A low interlock voltage often results from a simple unplugged connector that was not fully latched after previous service, so always check recent repair areas first.
The interlock loop is a safety circuit, and some vehicles will disable high-voltage operation entirely even if the low voltage is intermittent, leading to a no-start condition.
Corrosion inside a high-voltage connector can cause a low voltage signal without any visible external damage, so disconnecting and inspecting terminals is crucial.
This code can be set by a faulty component that is not the main battery pack, such as the inverter or charger, so do not assume the battery is at fault.
Aftermarket alarms or remote starters that tap into wiring can inadvertently affect the interlock circuit, leading to unexplained low voltage codes.

Can I keep driving with U3517?

Do not continue driving with this code present, as the high-voltage system may be disabled or in a unsafe state. Have the vehicle inspected by a qualified high-voltage technician before 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.