Inspection guide

What salt does to an electric car

Coastal cars are usually the best-kept vehicles on the market — garaged, low kilometres, carefully driven. They also carry a specific risk that has nothing to do with the battery and everything to do with what holds the car together.

On a combustion car, surface corrosion under the floor is an annoyance. On an electric car, corrosion at a high-voltage connector housing is a reason to stop the inspection.

Why an EV cares about salt

Salt-laden air accelerates galvanic corrosion wherever dissimilar metals meet and moisture can sit. That is true of any car parked within a few kilometres of the ocean or a bay, and it is why coastal vehicles across Australia show underbody corrosion years earlier than inland ones.

The battery pack itself is not the concern. Cells are sealed inside a case with its own thermal and moisture management, and salt in the air does not reach them or change their chemistry. What salt reaches is everything that fastens, seals and connects — and on an electric car some of those items carry several hundred volts.

Where it shows up first

Corrosion follows moisture, so it starts where water sits and air does not move. On most EVs that means the same short list every time.

• Subframe mounting points and suspension fasteners, particularly at the rear
• Battery pack case fixings and the underbody shielding that protects them
• High-voltage connector housings and their seals
• Brake components, which corrode faster on EVs because regenerative braking means the friction brakes are barely used
• Door and hatch seals, where trapped salt residue degrades rubber and opens water paths

Why the connector housings matter most

High-voltage cabling on a modern EV runs in shielded, sealed housings designed to keep moisture out of the connection. Once salt has attacked the housing or its seal, moisture can reach a live connection — and the car’s own isolation monitoring may only flag it once the fault is already established.

That is why isolation resistance testing is part of every inspection we run, and why it matters more on a coastal car than an inland one. A reading that has drifted from specification is not always dramatic on the day; it is a reliable early indication that water is finding somewhere it should not be.

What is fixable and what is not

Surface corrosion on fasteners and brackets, caught early, is a cleaning and treatment job — a few hundred dollars and worth negotiating over, not walking away from. Seized brake components are similarly routine.

Corrosion that has reached a structural mounting point, or that has compromised a high-voltage connector housing or the battery case fixings, is a different conversation entirely. Those repairs are expensive, sometimes uneconomic, and on a used car near the end of its warranty they are frequently the reason to buy something else.

The practical rule is simple: on any car that has lived near the water, the corrosion check is not an optional extra. Ask where the car has been parked, then have it verified rather than trusting the answer.

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