Why is My Low-Pressure Light On? And How to Fix It

Most people are familiar with their most important warning lights. It’s hard not to recognize these signs and symbols when your dashboard lights up in bright red. When you see a dreaded warning light, it is often pretty clear that something’s wrong, and you need to figure out the source of these issues and develop a repair plan.

There are several less well-known warning lights that, while they may not indicate impending emergencies, are still important to recognize and respond to quickly. Some of them make a lot of sense — a yellow “check engine” light means, of course, to take your car in and have a mechanic check your engine — but some aren’t as intuitive. For instance, the little yellow horseshoe with an exclamation point in the middle. What does that thing mean?

The horseshoe warning light is your low tire pressure symbol, and it means the air is low in one or more of your tires. You may be losing air quickly through a puncture, which is a problem you’ll need to address immediately. But even if you’re not facing an emergency situation, it’s a good idea to stop and refill flagging tires as soon as possible. Uneven pressure makes your tires wear differently from each other, which in the long run can lead to vehicle instability. Poor tire pressure also leads to lower fuel efficiency in your vehicle.

Tire Pressure and Temperature

It’s intuitive that leaks in your tire can cause low air pressure, but that’s not the most common reason for air pressure problems. More commonly, the weather outside of your tire affects the pressure inside. Hot temperatures increase air pressure; cold temperatures decrease it.

Why? Because of temperature-induced air contraction. Hot air expands, but cold air contracts. If your air pressure has been set during hot summer months, the air in your tire will lose volume when fall brings cooler weather to your area. If it was set in the winter, vice versa. In both cases, your air pressure light will probably come on when the seasons and the outdoor temperatures change.

Nitrogen-filled Tires

One way to account for this weather-induced air pressure change is by filling your tires with pure nitrogen, rather than with simple air. Although air contains around 80% nitrogen, that extra 20% makes a big difference. Nitrogen still responds to changes in temperature, but it doesn’t lose or gain as much volume as air does. Why? Water.

Oxygen easily combines with hydrogen to form water. There is always ambient moisture in the air, and no tire pump can account for it fully. Every time you fill your tires with air, moisture gets in. This vapor expands in the heat. Nitrogen-filled tires do not support moisture, so they will expand less than air does, causing less pressure fluctuation.

The moisture problem also causes corrosion inside your tire, contributing to overall tire wear. The water can freeze, causing damage inside the tire rubber. Nitrogen prevents this problem, giving your tires a longer life and saving you money.

There’s one more reason to use nitrogen: it leaks less! Rubber may seem solid from our perspective, but like anything else, it’s mostly space at the microscopic level. Nitrogen molecules are larger than oxygen molecules; pure nitrogen has a harder time escaping through the rubber.

Chapel Hill Tire can fill your tires with nitrogen for an affordable price, ensuring that they stay happy and your air pressure stays more even. You’ll see that funny horseshoe less with a nitrogen fill service.

Expert Tire Service at Chapel Hill Tire



You may have guessed it from the name, but we’ll tell you anyway — Chapel Hill Tire specializes in tire service. We can sell you tires, fill your tires, check your air pressure, patch leaks, fix flats, and fill you up with nitrogen, all for lower prices than you’ll find at any dealership. If your air pressure light comes on — or any other light, for that matter — just make an appointment and come on in. We’ll get you back on the road in no time, warning-light free.