Water ingress into a high voltage connector

Moisture has reached inside a high-voltage connector — a pack terminal, an inverter or motor plug, a charging inlet, or a sense-wire housing inside the battery.

This is the ordinary water-in-a-connector fault with the consequences changed, and the change is what earns it a separate entry. On a low-voltage circuit water causes a bad reading and some corrosion. Here it attacks the thing the whole system depends on: isolation, the electrical separation between several hundred volts and the metal bodywork a person can touch. So the same physical event that would be an annoyance elsewhere becomes the fault the car treats most seriously, and the response is usually to refuse to energise rather than to warn.

Where it gets in is predictable, and it is rarely the seal failing on its own. Connectors are opened for servicing and not reseated with their gaskets seated square. Pack cases are pressure-equalised through a vent whose membrane can be damaged or painted over. Charging inlets sit in the weather by design and drain badly once their channels silt up. And a pack mounted under the floor meets standing water, road salt and jet washes for its whole life — pressure washing near an underfloor pack or a charge port is a genuine cause rather than a caution.

Two properties make it hard to catch. It is often intermittent, appearing in rain or a wash and clearing as things dry, which reads as a phantom fault. And a connector can look perfectly dry by the time anyone opens it, having done its damage as a conductive film during the minutes it was wet. A fault that tracks the weather is this until proved otherwise, and that history is worth more to a diagnosis than any measurement taken on a dry day.

Drying it out is not a repair. Water that has been inside leaves corrosion and salts that keep conducting, so the connector and often its pigtail are replaced, and whatever let the water in is found — otherwise it returns with the next downpour.