No Clear Connection Between Soy-Coated Wiring and Rodents

Dear Car Talk:

Our daughter recently bought a used Toyota Highlander. Not one week after she took it home, the engine light came on. She drove back to the dealer and was told that critters had eaten the cover off some wires.

I've read that this has become a common problem not only for Toyota, but also for other car manufacturers, because they were covering the wires with a soy coating and animals like the taste. Is this true? If it is true, why are they doing it?

Now our daughter has to spray a peppermint mixture around her car every night to keep the mice, etc., away. Kinda goofy, don't you think? -- Dewey

Well, on the positive side, she probably has the best-smelling garage in the county. If the peppermint spray works, that's great. But she might also want to consider getting a cat to live in the garage and name it Peppermint. That might work better.

We don't know if this is true, Dewey. We do believe that manufacturers, in an attempt to use fewer plastic and petroleum products, started using some soy content as a petroleum replacement -- particularly in wiring insulation. What we don't know is if that attracts rodents or not.

Toyota denies the whole thing. They say that rodents damage all cars and all types of wires, and that they're "not aware of any scientific evidence that demonstrates rodents are attracted to automotive wiring because of alleged soy-based content." You can tell that was written by their lawyer because even the use of soy is "alleged."

Anyway, a bunch of Toyota owners didn't believe them. So, they filed a class-action suit, claiming Toyota is responsible for the cost of fixing their rodent damage. And in 2018, a judge dismissed the suit, pointing out that the rodents in question ate some stuff that was soy based and some stuff that wasn't soy based. According to the judge, they were just hungry, I guess. So, while this is a plausible-sounding theory and may prove to be correct someday, we haven't seen any evidence we can cite that blames soy content in wires.

What we can blame is rodents. We know they like warm places to make nests, like engine compartments. And we know they like to gnaw on stuff, because their teeth are always growing.

So my advice to your daughter would be to call in a rodent-control person. There are professionals who specialize in making places as inhospitable to rodents as possible. And that's what you want, because -- as your daughter found out -- small rodents can create large repair bills.


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