The U3541 code indicates a fault in the high‑voltage (HV) system interlock circuit, which is designed to keep the battery disconnected while the vehicle is running. When the interlock fails, the engine control unit (ECU) will not allow the high‑voltage system to energize, preventing the electric drivetrain from operating.
The relay that connects or disconnects the battery to the motor controller may be welded open, shorted, or mechanically stuck.
Corrosion, fraying, or a broken wire in the interlock circuit can break the signal required to engage the high‑voltage system.
A fuse or circuit breaker protecting the interlock circuitry may have tripped or blown, interrupting the circuit.
The module that monitors the interlock status may be defective, causing it to misinterpret the circuit state.
Although rare, a fault in the vehicle’s control unit software can incorrectly report an interlock fault.
No, the PCM is rarely the cause. Most U3541 faults stem from a failed interlock relay, damaged wiring, or a blown fuse. The PCM is considered only after those components are ruled out.
It physically connects or disconnects the battery from the motor controller, preventing the high‑voltage system from energizing when the vehicle is in operation.
The vehicle will likely not engage the electric drive and may have reduced performance or be unable to start in electric mode, but it can often run in a low‑power or assisted mode if the code is present.