A high-voltage interlock connector that is not fully latched or has backed out slightly; Damaged or corroded terminals within the interlock circuit B, often at the battery pack or inverter; Broken or chafed interlock wire in the harness, frequently near a service disconnect or underbody routing; Failed high-voltage component that houses the interlock switch, such as the battery pack disconnect or inverter cover; Water intrusion into a high-voltage connector causing a short or high resistance; Aftermarket or improper repair that bypassed or damaged the interlock loop; Control module internal fault misreading the interlock voltage

DTC codes / U35xx · Network communication / U3513

U3513High Voltage System Interlock Circuit B Low

Q: What does code U3513 mean?

High Voltage System Interlock Circuit B Low. U3513 indicates that the high-voltage system interlock circuit B is reporting a low voltage condition, which the vehicle's control module interprets as a break in the safety loop that protects technicians and occupants from exposed high-voltage components. The computer detects this when the interlock circuit's voltage falls below the expected threshold, typically because the loop is open or a connector is not fully seated.

U3513 indicates that the high-voltage system interlock circuit B is reporting a low voltage condition, which the vehicle's control module interprets as a break in the safety loop that protects technicians and occupants from exposed high-voltage components. The computer detects this when the interlock circuit's voltage falls below the expected threshold, typically because the loop is open or a connector is not fully seated.

SystemNetwork

Code typeGeneric (all makes)

SeverityHigh

Fix difficultyProfessional

AreaNetwork communication

Symptoms you may notice

High-voltage system warning light or message displayed on the dashboard
Vehicle may refuse to start or enter 'Ready' mode, especially in electric and hybrid models
Reduced power or limited operation mode, often called 'turtle mode'
Often no symptoms besides the warning light if the interlock circuit is only intermittently low
Inability to charge the high-voltage battery on plug-in vehicles
Audible alert or chime accompanying the high-voltage warning

Common causes, most likely first

A high-voltage interlock connector that is not fully latched or has backed out slightly
Damaged or corroded terminals within the interlock circuit B, often at the battery pack or inverter
Broken or chafed interlock wire in the harness, frequently near a service disconnect or underbody routing
Failed high-voltage component that houses the interlock switch, such as the battery pack disconnect or inverter cover
Water intrusion into a high-voltage connector causing a short or high resistance
Aftermarket or improper repair that bypassed or damaged the interlock loop
Control module internal fault misreading the interlock voltage

How to diagnose and fix it

Inspect all high-voltage interlock connectors for proper seating and latch engagement, starting at the service disconnect plug
Check the interlock circuit B wiring for continuity and resistance using a multimeter, following the manufacturer's service information
Verify battery pack voltage and inspect for any signs of coolant or water intrusion at high-voltage connectors
Perform a voltage drop test on the interlock loop to locate excessive resistance
Replace any damaged or corroded interlock connector or terminal as needed
If the circuit is intact, test the high-voltage component that contains the interlock switch and replace if faulty
Clear the code and perform a road test to confirm the repair, ensuring the interlock circuit reads within specification

Interlock Circuit B Low-Voltage Traps

A common mistake is replacing the high-voltage battery pack when the actual fault is a simple unseated interlock connector at the service disconnect plug.
The interlock circuit is a safety loop, so a low voltage reading can be caused by a perfectly functional system that has a slightly loose connector, not a failed component.
Some vehicles set U3513 after a low-voltage event or battery replacement if the interlock loop is not reinitialized properly, leading to unnecessary parts replacement.
Interlock circuit B often shares routing with other low-voltage circuits, so chafing from a nearby harness can cause intermittent codes that appear only on rough roads.
Always follow the manufacturer's high-voltage disconnect procedure before probing interlock circuits; the loop is designed to cut power, but capacitors can remain charged.

Can I keep driving with U3513?

Do not continue driving with an active U3513 code, as the high-voltage system may be disabled or in a reduced-power mode, and the safety interlock is compromised. 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.