U3525 indicates a fault in the high-voltage (HV) interlock loop circuit designated "G." The interlock is a low-voltage safety circuit that passes through HV connectors and components; the control system expects a continuous, correct-resistance path, and this code sets when that path is open, shorted, or reading out of range. When the fault is active the vehicle typically disables the HV system to prevent energized connectors from being unplugged.
The component monitored by circuit G—often an HV battery pack module, junction block, inverter, compressor, heater, or service disconnect—may have an internal interlock switch that is stuck open, shorted, or out of specification, breaking the loop.
Because interlock pins are small and pass through every high-voltage connector, a connector not fully seated, backed out secondary lock, bent pin, or corrosion can create an open or high-resistance condition in circuit G.
Chafing, pinching, moisture intrusion, or rodent damage can cause the interlock wire to short to ground, short to another circuit, or open, producing the out-of-range reading detected by the control module.
A replacement or repaired HV part that lacks the correct interlock pin configuration, resistor value, or connector alignment can fail the continuity check and set this code.
Although much less common, the module that reads the interlock circuit could have an internal sensing circuit issue; this should only be considered after the wiring, connectors, and components on circuit G have been verified.
It is not advisable. The vehicle usually disables the high-voltage system when an interlock fault is detected, which can cause sudden loss of propulsion power. Have it diagnosed promptly.
Usually no. The vast majority of U3525 faults are caused by a disconnected or damaged connector, wiring issue, or a failed component in the interlock loop itself. Replacing the control module should only be considered after the circuit and components are proven good.
Only if you have high-voltage safety training and the correct insulated tools and personal protective equipment. The orange high-voltage cables and components can deliver lethal voltage, so follow manufacturer lockout/tagout and de-energization procedures exactly.
"Circuit G" is simply the manufacturer’s label for one branch or segment of the high-voltage interlock loop. It identifies which portion of the safety circuit the diagnostic monitor is testing, helping narrow down which connector or component to inspect.