Are rats nibbling my car’s wiring because of a soy-based coating?
Dear Alex,
Twice, in my cousin’s new Toyota Aygo X, the oxygen sensor cable, which is exposed as there is no lower engine cover, has been chewed through by an animal. Apparently the cable covering is made from soy, which must be extremely attractive to animals. The dealer took no responsibility and she had to pay £370 for a new one. Two weeks later, the same thing happened again. When she threatened to return the car as being not fit for purpose, the dealer agreed to pay for the new cable and covered it in red grease. This is surely a build fault on the part of Toyota. What should we do?
– DH
Dear DH,
There seems to be some confusion about whether soybean oil is used in modern cars’ wiring, with even the manufacturers struggling to be able to say definitively either way. The issue is that so many of their components are sourced from a variety of third-party suppliers, who source their materials from elsewhere again, and tracing the exact composition of those materials is tricky.
It’s certainly not impossible, however, that coatings that contain soybean oil have found their way into cars as manufacturers attempt to reduce their reliance on petroleum-based coatings in wiring.
Does this make your wiring more attractive to rodents? No, not really, according to a scientific study carried out in 2020. It compared the attractiveness of petroleum-based PVC products to those based on soy by offering each up to rodents in a controlled environment, and found no statistically significant difference in the amount of gnawing that each product suffered.
That makes sense, when you think about it. By the time soy has been refined and turned into a plastic, it probably isn’t all that appetising to a rodent (in the same way that tallow doesn’t have quite the same appeal as beef to us humans).
The problem is more to do with the fact that rodents like to gnaw wires, full stop – regardless of what they’re made of. It’s not a new problem, and has been a source of aggravation for car owners long before soy was a factor.
If I were your cousin, I think I’d therefore focus on trying to reduce her car’s exposure to rodents by setting traps around the tyres, which is their usual route up into the engine bay. I understand peppermint oil is a good deterrent, too, or you can try spraying the wire in question with one of the various purpose-made rodent repellent sprays on the market.