Rust on coils

Gloria&Suzanne · Jul 3, 2026 at 4:01 AM

acp380 said: ↑

I recently started getting a really bad misfire situation on my 2012 prius. 3 of the 4 cylinders threw a misfire code plus a random misfire code. the cel came on while driving in the rain and the shuddering started soon after that. Mostly during light acceleration. Seems to smooth out during harder acceleration and at faster speeds.
Pulled the coils today and all 4 of them looked like water had gotten in. Heavy corrosion and powdery rust.
So I'm thinking this is my problem. Is water lethal to a prius coil? How do I prevent water from getting in again? I have taken the wiper cowl off several times in the cars life so I'm geussing that's were it's getting in. Is there any way to seal the coils better? BTW the car has about 250000 miles and the engine(and coils) about 80000 miles.also it has been weeks since the rain and the coils were dry. With the car intermittently running bad and getting poor mileage.
Click to expand...

Is it green? If so, that's copper corrosion. I found that in my 2013 Prius ignition coils today when I pulled each one out and inspected it. That can cause misfires. It's most commonly caused by moisture getting in somehow or oil leaking around the edges of the spark plugs.

Rust on coils

Gloria&Suzanne Junior Member

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Rust on coils

Gloria&Suzanne Junior Member