This is a call to action to check under the hood for rodent damage. In the past 10 years, we have seen a rise in rodent damage - and it's only gotten worse during the pandemic, as people aren't driving their cars as much.

From our observations, it does not seem like the rodents prefer one type of car over another; they are indiscriminate chewers.

Last month a customer brought in his 2013 BMW 535i. He stated that over the weekend, he saw a powertrain malfunction in the instrument cluster. Luckily, this customer was still able to drive the car and didn’t need it to be towed to the shop.

The first thing we did was connect the scanner and open the hood. It generally takes approximately 30 minutes just to connect the BMW factory tool and start the diagnostics. However, as soon as we opened the hood, we identified the culprit: Inside the engine bay, next to the intake manifold, was a rodent nest the size of a small watermelon.

Once we started getting data back from the scanner, we narrowed our search and discovered a range of malfunctions. We saw codes for the fuel pump, control module miscommunication, heated oxygen sensor circuit, catalytic converter and ultrasonic range sensor malfunctions.

Most of the codes came from components under the intake manifold. We called the customer, explained the problems and got his authorization to start work.We also asked him to call his insurance agent and start a claim. Rodent damage is often included in auto insurance coverage.

Once we removed the intake, we found that the rodent had eaten through several areas of the lower engine wire harness. This is often problematic; it’s extremely expensive to replace the entire engine wire harness.

This is where our customer got lucky a second time. On this particular BMW, there are four main engine wire harnesses, each of which is compartmentalized. It just so happened that the rodent only ate the bottom engine wire harness. The lower engine harness is less expensive to replace than repairing the complete engine wire harness.

Once we repaired the lower engine wire harness and cleared codes, we got the ultrasonic sensor (park distance control) code back. Because there was so much damage in the engine bay, we held off on checking the ultrasonic sensors, as they are behind the front and rear bumpers. We removed the front bumper because this code was for one of the front sensors, and we could see that the rodent also had eaten the ultrasonic sensor wires and the hood latch wires. The hardest part of this repair was to completely remove the front bumper and left front headlight assembly. Because the rodent only ate four wires in the front, we were able to repair the harnesses instead of replacing them.

Preventive rat tape

After both repairs, we performed one extra step: We rewrapped the lower engine wiring harness and the two-wire harness in the front of the car with rat tape. This tape is embedded with pepper oil. We have offered this for about eight years now, and the rodents never go back for seconds.

The reason rodents get into cars is because they are seeking a place to build nests, breed and sleep. They like dark and dry places to make a nest, so an engine compartment is the perfect place – especially now that people aren’t driving their cars as much due to the pandemic.

Once rodents make it into engine bay, they can do a lot of damage. Up until 10 years ago, car makers were using petroleum-based products, such as PVC, to make wiring insulation. But as the cost of oil went up and green initiatives went into full swing, manufacturers began to produce soy-based wire harness insulation or wrappings. Soy is less expensive than crude oil and is much safer for the environment, but it’s also the ideal food source for rodents.

So, if your car has been sitting for a while or is parked near shrubs, check under the hood for rodent activity. Look for nests, twigs, leaves, insulation, acorns and feces. If you see any signs, take action before it adds up to a large bill or leaves you stranded.

In the case of the BMW 535, the insurance did pay approximately 95% of the repair, but it does not always go that way.

Matt Pataky owns Sunnyvale Foreign Car Service, 15 Pioneer Way, Mountain View. For more information, call 960-6988, email or visit