Even with regular checks, you might notice abnormal tire pressure—like a sudden drop or a tire that’s always underinflated. Ignoring these issues can lead to bigger problems, but knowing how to respond can save you time and money. Here’s what to do when your tire pressure is off, and when to call for help.

First, let’s define “abnormal.” A normal pressure change is 1-2 PSI with temperature shifts. Abnormal is a drop of 5+ PSI in a week, or a tire that’s underinflated even after adding air. If you see this, start with a visual inspection. Look for obvious issues: a flat tire (easy to spot), a nail or screw in the tread, or a damaged valve stem (cracked, bent, or missing the cap). If you find a nail, don’t pull it out—this will make the leak worse. Instead, drive slowly to a mechanic to get it patched.

If there’s no visible damage, check the valve stem. A faulty valve stem is a common cause of slow leaks. To test it, mix soapy water in a spray bottle and spray it on the valve stem. If bubbles form, air is leaking—you’ll need to replace the valve stem (a cheap, quick fix at most tire shops). Don’t forget to check the valve cap—missing or loose caps let dirt and moisture in, which can damage the valve.

If you’re on the road and notice low pressure (via TPMS light or a flat tire), pull over to a safe, level spot (not the highway shoulder if possible). Turn on your hazard lights. If you have a spare tire, replace the flat one following your owner’s manual instructions. Most spare tires are “donut” tires—smaller and designed for short distances (usually 50 miles or less) at low speeds (50 mph max). Don’t drive on a donut for longer than needed.

If you don’t have a spare, or the tire is too damaged to replace, call a roadside assistance service (like AAA) or a tow truck. Never drive on a severely underinflated or flat tire—this can ruin the tire’s structure, damage your wheel, and cause a blowout.

Warning signs to watch for: a TPMS light that flashes then stays on (this means a system error, not just low pressure), a tire that feels “wobbly” when driving, or a burning smell from the tire area. These are signs of serious issues—stop driving immediately and get help.

By acting fast and knowing the right steps, you can turn a stressful tire issue into a minor inconvenience.