Eddie spent 35 years in the automotive business with Honda. He is an ASE Certified Master Technician and has bruised knuckles to prove it.
So is the low tire pressure warning light on or is your TPMS light on? There is a difference, and the repair is very different depending on which warning light is on.
1. "Low Tire Pressure" Warning Light
If the low tire pressure warning light is on in your vehicle—the warning light with the icon of a tire with an exclamation point in the middle—the most likely cause is low tire pressure.
This warning light could be caused by any of these:
- an obstruction in the tire like a nail or screw;
- neglect (not setting tire pressures to manufacturer's specs at every oil change or every two months);
- or a seasonal drop in outdoor temperatures.
All tires, even tires in good condition, lose air for a number of reasons, but mostly because tires are porous. It's common to lose at least 1.5 psi per month naturally. But there is also scientific evidence that tire pressures drop with colder temperatures, so you could expect to lose at least 1 psi for every 10 degrees drop in temperature.
The NHTSA (National Highway Traffic Safety Administration) regulations state that the low tire pressure light indicator must come on when the tire pressure drops 25% below the listed recommended inflation pressure. Some manufacturers have stepped it up a notch and have set their tolerances to no more than a 20% drop in pressure before the light comes on, so check your owner's manual for more information.
What To Do If Your Low Tire Pressure Warning Light Comes on
If your low tire pressure warning light comes on, don't panic! Here are some steps you can take before you bring it into the garage;
1. Do a visual inspection of all your tires; make sure one is not flat. The spare tire counts too!
2. Check all your tires for proper inflation: about 32 psi in warm temperatures, 35 psi in cold temperatures.
3. If one tire has lower tire pressure then the other three, check it over for a nail or screw in the tire tread.
4. If you want to look for the leak, use a spray bottle with a water and dish soap mixture, spray the complete tire and rim, and then watch for bubbles.
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Low Tire Pressure Means You Need to Put in More Air
Think of it like this: The low tire pressure light is like a low fuel light. When it's on, it means you need to put air in your tires, just like you would put more fuel in your car if it was low on fuel. Ultimately, it's the driver's responsibility to keep an eye on the vehicle's tire pressures, and having low tire pressure sensors in each tire will help you maintain proper inflation.
Why Is My Tire Pressure Low in the Winter?
Let's say you took your car in for an oil change in late August, and the temperature outside is a balmy 85 degree. The mechanic sets the tire pressures in your vehicle to 32 psi because it's recommended by the factory sticker in the driver's door jamb. Fast forward to late November or early December, and the temperature outside has dropped to 30 degrees (something that is very common in New England) and your low tire pressure light comes on.
You bring your vehicle in for its next oil change and the mechanic tells you that the tire pressures are all at just 24psi. Not only have you lost tires pressure naturally from being porous, but you have also lost tire pressure because of the 55-degree change in temperature. It's always best to set the tires' pressures to the "cold" inflation settings just before the cold temperatures set in. This will help prevent the pesky low tires pressure warning light from coming on so often.
The Nitrogen Work-Around
If you would like to take it one step further in trying to prevent the low tire pressure light from coming on, you could try filling your tires with nitrogen. A lot of dealerships and tire stores have had nitrogen filling stations installed since tire pressure monitoring systems have been implemented.
Filling your vehicle tires with nitrogen will reduce fluctuation in tire pressures because nitrogen has less water vapor in it than regular air does. It's not a perfect system or a permanent fix, but it does reduce the visits to the air pump or garage. It also comes with a price: usually around $100 for lifetime nitrogen fill, but ask your dealer for more information.
2. "TPMS" Warning Light
If the TPMS light is on, most likely you have a problem with the tire pressure monitoring system, for example a malfunctioning tire sensor. If all tire sensors are working properly, you may have to dig a little deeper to figure out what's causing the light to come on; you may even have a faulty control unit.
What to Do if Your TPMS Light Comes on
If the TPMS warning light is on, bring the car to the dealership, because there is something wrong with the tire pressure monitoring system.
Questions About TPMS or Your Low Tire Pressure Warning Light?
If you have any questions about your low tire pressure warning light, TPMS light, or nitrogen, feel free to ask and I will be glad to answer them as best as I can.
This article is accurate and true to the best of the author’s knowledge. Content is for informational or entertainment purposes only and does not substitute for personal counsel or professional advice in business, financial, legal, or technical matters.
Questions & Answers
Question: Can my mechanic put air into a tire when there is still a nail in the tire?
Answer: It would be a better idea to remove the nail and plug the tire because the tire is just going to lose pressure again and you could possible destroy the tire.