A high-voltage connector that is not fully seated or has a damaged interlock pin; Corrosion or water intrusion in a high-voltage connector or interlock circuit; A faulty high-voltage component cover or service disconnect plug not properly installed; Damaged wiring harness in the interlock circuit, often from chafing or rodent damage; Failed interlock switch inside a high-voltage battery pack, inverter, or motor; Internal fault in the control module that monitors the interlock circuit; Aftermarket or improper repair that bypassed or altered the interlock loop

DTC codes / U35xx · Network communication / U3545

U3545High Voltage System Interlock Circuit P

Q: What does code U3545 mean?

High Voltage System Interlock Circuit P. U3545 indicates that the high-voltage system interlock circuit for the 'P' loop 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 loop that runs through high-voltage connectors and covers; when it opens or shorts, the module sets this code to prevent high-voltage exposure.

U3545 indicates that the high-voltage system interlock circuit for the 'P' loop 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 loop that runs through high-voltage connectors and covers; when it opens or shorts, the module sets this code to prevent high-voltage exposure.

SystemNetwork

Code typeGeneric (all makes)

SeverityHigh

Fix difficultyProfessional

AreaNetwork communication

Symptoms you may notice

Illumination of the high-voltage system warning light or service vehicle soon message
The vehicle may refuse to start or enter 'ready' mode, leaving you stranded
Reduced power or a forced limp-home mode if the vehicle does drive
High-voltage system may be automatically disabled, preventing EV or hybrid operation
Often no symptoms besides the warning light if the fault is intermittent
Possible audible alert or chime accompanying the warning

Common causes, most likely first

A high-voltage connector that is not fully seated or has a damaged interlock pin
Corrosion or water intrusion in a high-voltage connector or interlock circuit
A faulty high-voltage component cover or service disconnect plug not properly installed
Damaged wiring harness in the interlock circuit, often from chafing or rodent damage
Failed interlock switch inside a high-voltage battery pack, inverter, or motor
Internal fault in the control module that monitors the interlock circuit
Aftermarket or improper repair that bypassed or altered the interlock loop

How to diagnose and fix it

Inspect all high-voltage connectors for proper seating and visible damage, reseating any that are loose
Check the service disconnect plug and high-voltage component covers for correct installation
Perform a visual inspection of the interlock wiring for chafing, corrosion, or rodent damage
Use a scan tool to read live data for the interlock circuit voltage and compare to specifications
Measure resistance or continuity of the interlock loop at each connector to isolate the open or short
Test the interlock switch or sensor at the suspect component and replace if faulty
If the circuit checks out, diagnose or replace the control module that set the code

Interlock faults often hide in plain sight

A common oversight is a high-voltage connector that looks latched but is not fully engaged, causing an intermittent interlock voltage spike.
The code can be set by a low 12-volt battery or poor ground, so always verify the base electrical system before condemning high-voltage parts.
After any high-voltage repair, the interlock loop must be fully restored; bypassing it to 'make it run' is dangerous and will reset the code.
Some vehicles set U3545 when the service disconnect plug is removed with the key on, even though no actual fault exists.
Interlock circuits are often daisy-chained through multiple components, so a fault in one connector can disable the entire high-voltage system.

Can I keep driving with U3545?

Do not drive the vehicle if the high-voltage warning is active, because the system may be disabled or unsafe; have it towed to a qualified technician. If the light is intermittent and the vehicle drives normally, avoid high-voltage operations and schedule service promptly.

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.