If you live in the United States and drive a vehicle manufactured after 2008, then your car likely came equipped with a tire pressure monitoring system (TPMS). These government-mandated systems alert you to low tire pressure conditions, allowing you to act before suffering potentially severe damage. Depending on your car's model, your TPMS may or may not indicate which tire has a problem.
Once you have a warning light, there are a few steps you'll need to take to repair the issue. Since driving on an underinflated tire can be dangerous, always act as soon as possible once you see the warning light. After you've arrived at a gas station or another safe location, follow these three steps.
1. Check for Signs of Catastrophic Damage
Start by looking for evidence of severe damage to your tires. You likely won't be able to spot relatively minor damage while the car is on the ground, but you can look for evidence of missing tread, damaged sidewalls, and so on. You're more likely to find this type of damage if your TPMS warning light came on after you hit a severe pothole or some other road hazard.
If you see severe damage, do not add air to your tire and continue driving. Damaged tires may fail suddenly, so it's a good idea to tow your car to the nearest tire shop. Technicians can evaluate the damage to determine if you can repair the tire or if you'll need a new one.
2. Check Your Tire Pressure
If your car's TPMS doesn't tell you the individual pressure at each tire, you'll need to check manually to determine the problem. It's a good idea to carry a small tire pressure gauge with you for precisely this purpose, but you can also use the air pump found at most gas stations. Tire pressure can vary with air temperature, so don't worry if every tire is a few psi below where you'd expect.
However, one tire with a noticeably lower pressure than the others might indicate trouble. If the tire isn't completely flat, add some air and continue monitoring that tire's air pressure for the next few days. Continuing air loss, even if it's minor, means you likely have a puncture or some other form of damage.
3. Schedule Repairs
If you have a tire that's slowly losing air, the best and cheapest option is to schedule a tire repair as soon as possible. Punctures and damage can worsen over time, eventually becoming severe enough that a repair will no longer be an option. Promptly scheduling repairs gives you the best chance of repairing your tire and saving yourself from the potentially high cost of replacement.