If COVID-19 left you sedentary for a large portion of 2020, chances are you had some leaves or debris to clear out from under the hood of your vehicle once it came time to hit the road again.

If you experienced car problems after a long period of the family vehicle sitting dormant in the garage, it may be tempting to just chalk it up to needed routine repairs you had to delay due to the pandemic.

Look closer though.

Whether urban, suburban, or rural – four-legged intruders have the penchant for nesting in parked vehicles (they’re large and they’re dark) and wreaking havoc.

From gnawed wires… to chewed and mauled upholstery and insulation blankets… to nesting material catching alight – mice, rodents, squirrels, chipmunks and other vermin outstaying their welcome in an unused vehicle increases the likelihood of a vehicle malfunction.

Such incidents are especially common in Forensic & Failure Analysis’s home city of Syracuse, NY – designated in a recent article, as one of the”rattiest cities” in the United States, along with its upstate neighbors Buffalo and Albany.

In an article published by the ‘New York Times,’ Dr. Michael Parsons of Fordham University keenly pointed out that just as cars remained dormant during the pandemic, business lockdowns deprived rodent colonies of their traditional hangouts… when a restaurant dumpster was no longer affording a meal in the days’ uneatened food, rats went searching for alternate sources of food.

Finding Fault

Who, then, is at fault when nature’s creatures infiltrate and cause billable damage or perhaps a fire to a car, truck or tractor?

Major vehicle manufacturers are giving a resounding “Not Us!”

Toyota finds themselves in their second class action suit in a decade over car owners demanding reimbursement for damages caused by rats nibbling through vehicles’ soy-based wire insulation.

Toyota switched from chloride-based to soy-based wire insulation in the 2010s, an environmentally-conscious measure that surely delighted vermin, who exercise their teeth and jaws on all things easy to chew.  The theory is that the plant material based insulation is more attractive to the rodents.

An article published in May 2021 by the blog “Top Class Action” reports that the case against Toyota has been rekindled after being tossed out by a US District Court judge in 2018, citing the soy coating was a design defect not covered by express warranty.

The current suit is pending as of the publication of this web page.

Nesting Fire Forensic & Failure Analysis

From the FFA Archives – nesting material retrieved from a vehicle fire.


Signs That You Have An Intruder

There is more practical gain in preventive maintenance than taking the “Goliaths” of car manufacturing to court for long, costly trials. Taking a cue from an article by Modern Pest, Forensic & Failure Analysis has compiled a series of tips for abating vermin in your automobile:

  • Take a whiff! The nose knows bad smells … and rodent urine is pungent as is that of a dead rodent. If present, these odors will likely waft through the vehicle’s air vent. The vent system is a prime tunnel for vermin to make their way from the engine bay to the vehicle’s interior. Look for visual signs of rodent droppings as well.
  • Look for food sources in unlikely places including “standard rodent faire” like seeds, acorns, even pet food.  If you hear a noise when the cabin fan is turned on, it may be materials brought in by rodents in the fan housing.
  • Check the car’s airbox, where the engine air filter is located. This is a go-to for rodent habitation and nest building, as it is warm and shields them from the elements. An airbox should be (kept) relatively clean, so if you do have an intruder, it will be obvious. If your vehicle has a plastic engine cover, or tiny compartments in the trunk, check for evidence of nesting there too.
  • An obvious one – if you see a mouse or a rat scampering around your vehicle, be diligent and search for signs of an infestation in your car. Rodents travel in colonies, and packs consist of multiple alpha males and females. That means breeding… and that means more rodents!

Whether Idle or In Use

A note about sedentary vehicles – the longer a vehicle sits – the more likely it is for this to be a potential problem.

Forensic & Failure Analysis has seen cases of daily use vehicles with rodent intrusion as well. Many factors play into this such as the cleanliness of the vehicle (in particular food attractants) and the location where the vehicle is parked (such as near a dumpster or near trees with a heavy squirrel population).

Where There’s Smoke…

Although not an all inclusive list, there are two major issues of concern relating to fire causation and rodents in vehicles.  The first is combustible nesting material near high temperature heat sources such as the vehicle exhaust header (See aside at bottom of page).

The second is that rodents can damage insulating materials such as the wire insulation. This can cause wires of different voltage potential to short circuit or have high resistance heating occur when the conductor itself is damaged.

Squirrel Cage Car Forensic & Failure Analysis

A car owner prepares to clean a mouse nest from a vehicle’s fan blower motor cage, also known as a squirrel cage. It was lined with a dryer sheet, leaves, and twigs.

Abatement Techniques

  • We’ll start this list with an obvious technique – if you own a vehicle that you do not drive frequently, take it out for a spin once in a while to disperse your unwanted visitors from their makeshift home.
  • Peppermint oil is a natural rodent repellent. Either droplets in a spray bottle (be careful of your mass airflow sensor and your heat shield) or soaked cotton balls placed in the vehicle’s cabin and under the hood can aid with warding off intruders. Cloves and cayenne pepper also work.
  • Assault their stimuli. Rodents can hear ultrasounds humans cannot, and apparatuses such as the E-Pro Triple Attack Rodent Repeller provides a 360 area sweep with sound and pressure frequencies rats can’t stand.
  • Traps and poisons are likely to bring at least a few rodents’ intrusions to a halt. Be sure you’re mindful of domestic pets you have around your vehicle (or area where a dormant vehicle is parked or kept). There are humane cage “catch and release” traps, but relocating the captured intruders can occasionally prove tricky.


Forensics entails considering a large number of factors, situations and “what if’s” to determine causation of an event. With vehicle failure, it may be a consideration, even a preference – to point the finger at the manufacturer or mechanic.

Rodent infestation and damage to vehicles, especially in the aftermath of COVID-19, proves that determining cause always commands keen detective work, even if the answer is scampering and scurrying right in front of us.

Forensic & Failure Analysis has conducted and completed analyses on failures of all different types of vehicles. Learn more here, or contact us.

Tractor Fire Damage Forensic & Failure Analysis

It’s not just rodent colonies that cause commonplace vehicle failures. FFA handled a case where this tractor caught fire. Nesting material including a bird’s egg was discovered near the engine exhaust.