U3517 indicates that the high‑voltage (HV) system interlock circuit C is reading a low voltage condition, meaning the safety loop that verifies the presence and proper connection of HV components is open or shorted to ground. When this fault is detected the vehicle disables the HV system as a safety precaution.
A short to ground, an open circuit, or a broken wire in the harness can pull the interlock signal low. This is the most common source of the code.
The mechanical or solid‑state switch that monitors HV component seating can wear out or become mis‑aligned, causing an abnormal low reading.
A fault inside the battery pack, inverter, junction box, or other HV device can short the interlock circuit to ground, triggering the code.
If the 12 V source that powers the interlock circuit is insufficient or noisy, the circuit may not reach the proper voltage level.
Moisture or contamination at the interlock connectors can increase resistance, preventing the circuit from maintaining the correct voltage.
The control module that processes the interlock signal can develop a hardware or software fault, but this accounts for only a small percentage of cases.
No. The PCM/ECM is rarely at fault; most cases are caused by wiring, connectors, or the interlock switch itself. Replacing the computer without fixing the underlying circuit usually does not resolve the code.
Most manufacturers disable the HV system when U3517 is active, which means the vehicle may not move or will be limited to a limp‑home mode. It is safest to have the vehicle towed for diagnosis and repair.
Any qualified HV‑certified technician, independent shop, or dealer can diagnose and repair the interlock circuit. The repair does not require a specific brand service center.
If the underlying fault is not repaired, the code will typically return and the warning will stay on. Clearing the code without fixing the cause is only a temporary measure.