U3516 indicates the high-voltage safety interlock circuit labeled "C" is reporting electrical values outside the expected range—typically high resistance or intermittent continuity—while remaining partially complete. This circuit is a series loop that runs through specific high-voltage connectors or service disconnects; the control module monitors it to ensure high-voltage components are properly connected before energizing the system. A performance fault suggests loose terminals, corrosion, or wiring damage rather than a clean open circuit.
The most common cause is oxidation or fretting on the interlock pins within the high-voltage connectors that Circuit C passes through, creating high resistance that fluctuates with vibration or temperature.
A connector that is not fully locked or a service disconnect that is not completely seated can bridge the circuit intermittently, causing erratic resistance readings without triggering a full 'Open' code.
Wire insulation damage allows moisture entry or creates intermittent shorts to ground, altering the circuit's resistance; common in underbody harnesses exposed to road spray.
The mechanical switch or shorting bar inside the service disconnect or component connector may have worn contacts, creating internal resistance above the calibrated threshold.
Rarely, the internal sensing circuit within the control module that evaluates interlock voltage may drift or fail; this should only be considered after all physical wiring and connectors are verified good.
'Performance' means the circuit is electrically complete but its resistance is too high or it is behaving erratically, whereas 'Open' indicates a total break in continuity. Performance faults are often caused by corrosion or loose pins rather than a disconnected plug.
No. The high-voltage system is likely disabled or in a safe-state shutdown to prevent energization with a compromised interlock; the vehicle may not start or may immediately shut down, and propulsion power will be severely limited or absent.
No. Although the module stores the code, the root cause is almost always in the physical interlock wiring, connectors, or service disconnect. Replacing the control module rarely resolves this specific code.
No. High-voltage interlock systems are part of circuits that may contain lethal voltage. Diagnosis and repair should only be performed by qualified technicians using insulated tools and following high-voltage safety protocols, including wearing appropriate personal protective equipment and disabling the high-voltage system via the service disconnect.