Loose or improperly seated high-voltage connector on circuit B; Damaged interlock switch or wiring within a high-voltage component; Corrosion or water intrusion in a high-voltage connector; Faulty high-voltage battery pack interlock circuit; Failed inverter or converter interlock switch; Chafed or broken interlock wire harness; Software glitch in the control module managing the interlock loop

DTC codes / U35xx · Network communication / U3512

U3512High Voltage System Interlock Circuit B Performance

Q: What does code U3512 mean?

High Voltage System Interlock Circuit B Performance. U3512 indicates that the high-voltage interlock loop circuit B has reported a performance fault, typically a voltage reading outside the expected range, to the vehicle's control module. The interlock is a safety circuit that confirms all high-voltage connectors and covers are properly seated before allowing the high-voltage system to energize.

U3512 indicates that the high-voltage interlock loop circuit B has reported a performance fault, typically a voltage reading outside the expected range, to the vehicle's control module. The interlock is a safety circuit that confirms all high-voltage connectors and covers are properly seated before allowing the high-voltage system to energize.

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 if the vehicle does drive
High-voltage system may be disabled entirely, preventing EV operation
Often no symptoms besides the warning light if the fault is intermittent

Common causes, most likely first

Loose or improperly seated high-voltage connector on circuit B
Damaged interlock switch or wiring within a high-voltage component
Corrosion or water intrusion in a high-voltage connector
Faulty high-voltage battery pack interlock circuit
Failed inverter or converter interlock switch
Chafed or broken interlock wire harness
Software glitch in the control module managing the interlock loop

How to diagnose and fix it

Inspect all high-voltage connectors for proper seating and visible damage
Check for corrosion or water intrusion at each interlock connector
Measure interlock loop continuity and resistance with a multimeter
Verify interlock switch operation at each high-voltage component
Inspect wiring harness for chafing, breaks, or loose pins
Clear the code and test-drive to see if the fault returns
If hardware checks pass, update or reprogram the control module

Interlock faults that mimic component failures

A partially latched connector can pass a visual inspection but still set U3512 because the interlock switch does not fully close.
Water intrusion in a high-voltage connector often causes intermittent U3512 codes that appear only after rain or car washes.
Technicians sometimes replace expensive high-voltage components when the real fault is a chafed interlock wire in the harness.
The interlock loop is a low-voltage safety circuit, so a failure does not necessarily mean the high-voltage system itself is damaged.
After any high-voltage repair, the interlock loop must be fully reconnected and verified before clearing codes, or U3512 will reset immediately.

Can I keep driving with U3512?

Do not drive the vehicle if the high-voltage system warning is active, as the high-voltage system may be disabled or unsafe. Have the vehicle inspected by a qualified high-voltage technician before attempting to move it under its own power.

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.