What Does The Tire Pressure Light Mean?

There’s a horseshoe-shaped warning light on your car's dashboard with an exclamation point in the middle. This is your tire pressure light, also known as the TPMS light.

TPMS is short for Tire Pressure Monitoring System. You can find this system on all modern passenger vehicles, and it consists of a set of sensors on each tire, connected to a central computer. When the pressure on one or more tires drops too low, the computer will register the drop, and the warning light will come on.

But what does this mean for you, the driver? Let’s talk about what the tire pressure light means and what you should do when it lights up.

Tire Pressure Basics

Before we talk about the TPMS light, let’s discuss tire inflation. 

Even properly-functioning tires bleed a small amount of air every day. Over time, that tiny amount adds up, and your tire pressure drops. Your tire pressure also changes with temperature. For every 10 degrees Fahrenheit of temperature drop, the pressure will drop by 1 pound per square inch. For every 10 degrees of temperature increase, the pressure will rise.

You fill your tires on a beautiful, 80-degree summer day. Two months later, when it’s 60 degrees out, you’ll be underinflated by 2 PSI. A few months after that, when it’s 30 degrees out, you’ll be short by 5 PSI.

Why does this matter? Here are a few reasons:

• Underinflated tires wear down faster. As the pressure is lower, the tire becomes squishier, and more of the rubber is exposed to wear and tear. The longer this goes on, the more the tire edges wear down, leading to a premature blowout.
• You also get worse traction. In the rain, snow, and other adverse conditions, you won’t have enough grip to maintain control of your vehicle. This can cause you to skid and slide around the road, even if you’re an experienced snow driver.
• Poor inflation will reduce your gas mileage. Each wheel turn requires more energy because the flabby tires are more difficult to turn, which translates directly to a loss of fuel efficiency.

Incidentally, overinflated tires also pose some serious safety risks. The point isn’t always to have as much pressure as possible. The point is to have the correct pressure for your tires and vehicle.

What Does The TPMS Light Mean?

In its most basic sense, the TPMS light indicates that your tire pressure is too low or too high. But there are a few other things to be aware of. For one thing, it’s normal for most or all of the lights on your dashboard to illuminate when you start the engine. If the TPMS light turns on alongside other lights and then turns off, there’s nothing wrong.

Here are some of the things you might encounter when the TPMS light is illuminated:

• The TPMS light comes on and stays on. When this occurs, at least one of your tires’ pressure is too low or too high. If this frequently occurs, it’s worth checking your tire for a slow leak. As soon as convenient, stop at a service station with an air compressor and adjust the pressure as needed.
• The TPMS light turns on intermittently. This typically happens when your tire pressure is borderline. Let’s say you wake up in the morning, and it’s 40 degrees out, and your pressure is 2 PSI too low. You drive to work, and the TPMS light is on. When you leave work, it’s 60 degrees out. Now the pressure is perfect, and the TPMS light is off. The light may even turn off mid-drive, as the friction from driving heats up your tires.
• The TPMS light flashes for a minute, then stays illuminated. This is a less common warning but means something is wrong with your TPMS system. It may be the computer, a faulty wire, or one of the individual sensors. You’ll want to take it to a mechanic to diagnose the issue.

Do I Still Need to Do Manual Pressure Checks?

A TPMS warning light is a helpful tool, but it’s still just a tool. You’ll always want to verify your tire pressure manually before making any adjustments. Along the same lines, it’s wise to check your pressure regularly, even if the warning light is not illuminated. There are a few good reasons for this:

• There may be a defective sensor that does not detect a pressure drop.
• When hauling or towing, the TPMS system may be calibrated incorrectly for the vehicle load.
• The light is just a general warning. It doesn’t tell you which tire has the wrong pressure, whether it’s a combination of tires, or whether the pressure is too low or too high.

In other words, it’s still important to know how to check your tire pressure manually.

How Do I Manually Check My Tire Pressure?

To check your tire pressure, you’ll need a tire pressure gauge, which you can find for a few dollars at any automotive shop. You’ll also need to know what the correct pressure is. This figure is typically located on a decal inside the driver’s side door jamb. Alternatively, you can find it in your owner’s manual.

Check the pressure, and add or drain air as necessary until it’s correct. And don’t panic if the TPMS light stays on. The computer can take up to 200 miles to reset and shut the light off.

Summary

Your car’s tire pressure light is far from foolproof, so it’s always important to follow up. By performing manual checks and regularly topping off your tires, you’ll have a safer, more fuel-efficient driving experience.

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