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Plastic Undercarriage Cover: Why Does My Vehicle Have One?

A Prius s undercarriage. A plastic undercarriage tray protects your vehicle's sensitive components.

A plastic undercarriage cover is something you’ll find on almost any modern vehicle. If you’ve ever looked underneath a late-model car or truck, chances are you’ve been surprised by how much plastic has been tucked up there, typically around drivetrain components at the front and middle of the chassis.

What do those trays do? Are they necessary, or just an accessory? Read on to find out.

Protect Yourself

A plastic undercarriage cover is designed to protect the wires and sensors that are included with newer cars and trucks. With cables that hang down and sensors that stick out, there’s always a chance that a branch or road debris will snag something important and sever a wire or disconnect a crucial component. An undertray goes a long way towards preventing that from happening.

Consider the Aero

On performance vehicles, the air that flows underneath the bodywork is just as important as that which passes over the top. In order to reduce drag at higher speeds, many models now come with a plastic undercarriage cover that smoothes out the nooks and crannies below.

Plastic undercarriage tray

These trays are installed on more common vehicles in order to improve their fuel mileage, again, by reducing drag as much as possible.

A plastic undercarriage cover can also direct air where it needs to go, rather than relying on the simple flow to cool brakes and transmissions, for example. Also, air is often diverted up into the radiator at the front of a car or truck with a small dam that can be part of a plastic tray.

Don’t Remove Them

You’ve probably had at least one or two brushes with the pavement when driving a car equipped with a plastic undercarriage cover, and heard a scuffing sound when it’s dragged across the asphalt. Don’t be concerned — it’s doing what it was designed to do by taking the hit so that your wires and sensors stay safe.

It’s certainly not any indication that it should be removed so that the scraping doesn’t happen again. In fact, removing these trays can have a negative impact on your fuel mileage, vehicle performance and, of course, the protection of sensitive components. Keep it in place, and trust that the engineers who designed your automobile included a tray for the right reasons.

Check out all the exterior products available on NAPA Online or trust one of our 17,000 NAPA AutoCare locations for routine maintenance and repairs. For more information on your vehicle’s undercarriage, chat with a knowledgeable expert at your local NAPA AUTO PARTS store.

Photo courtesy of Flickr.

Benjamin Hunting View All

Having been bitten by the car bug at a young age, I spent my formative years surrounded by Studebakers at car shows across Quebec and the northeastern United States. Over ten years of racing, restoring, and obsessing over automobiles lead me to balance science writing and automotive journalism full time.  I currently contribute as an editor to several online and print automotive publications, and I also write and consult for the pharmaceutical and medical device industry.

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