Lesson: How Your Tire Pressure Monitoring System Works

Your car’s Tire Pressure Monitoring System (TPMS) is a quiet helper that watches your tires while you drive. This lesson explains the two ways it works, how to read its warnings, and where its job ends and yours begins.

Part 1: Two ways a car can watch your tires

TPMS monitors tire pressure either through sensors located in the tires (a direct system) or through wheel speed and other vehicle sensors (an indirect system). The information goes to an on-board processor, which interprets the signals and lights the TPMS symbol on your dashboard when pressure falls below an acceptable level. ^[NHTSA]

All passenger cars, light trucks and vans from model year 2008 or newer are required to have TPMS. Some 2006 and 2007 models have it too; for those years, check the owner’s manual or ask a dealer. ^[NHTSA]

Part 2: Recognize the symbol

The federal standard allows two low-pressure warning symbols: a tire cross-section with an exclamation mark inside, or a top view of a car with all four tires showing. Either one lights up when tire pressure is significantly underinflated. ^[NHTSA]

Part 3: Read the three warning patterns

Pattern A: The light comes on and stays on

At least one tire is significantly underinflated. NHTSA advises inspecting your tires and checking the pressure as soon as possible; the light goes off once the tires are properly inflated. ^[NHTSA]

Pattern B: The light goes on and off

On cold mornings the light may come on briefly and then turn off. This is likely marginally low pressure that drops below the threshold overnight and rises as the tires warm from driving or warmer air. You should still check your tires; the light shouldn’t come on when they’re properly inflated. ^[NHTSA] This is why the light often appears when the weather first cools: tire pressure drops as outside temperature drops. ^[NHTSA]

Pattern C: The light flashes, then stays on

TPMS on 2008 and newer vehicles must detect and warn when the system itself isn’t working. A malfunction may show as the symbol flashing for 60 to 90 seconds and then staying lit, repeating at every start until it’s fixed. NHTSA says to contact your dealer for a system inspection. ^[NHTSA]

Part 4: Where TPMS stops and your gauge starts

TPMS warns only when a tire is significantly underinflated, so NHTSA still recommends a monthly gauge check. ^[NHTSA] Underinflated tires are visually difficult to detect, and the system isn’t meant to replace regular tire maintenance. ^[NHTSA] The stakes are real: NHTSA says underinflation is the leading cause of tire failure, and tires lose some air naturally even without a puncture. ^[NHTSA]

Here’s NHTSA’s step-by-step method: ^[NHTSA]

1. Find the recommended pressure on the Tire and Loading Information label on the driver’s door edge or post, or in the owner’s manual. Use this number, not the one on the tire.
2. Check all tires, including the spare.
3. If a tire is too high, release air gently with the edge of the gauge until it’s correct.
4. If it’s low, note how many pounds are missing and add that amount.
5. Recheck that all tires match, unless the front and rear are meant to differ.

If you’ve been driving and the tires are warm, NHTSA says to fill to the recommended cold pressure; being slightly low is safer than being significantly low, and you can recheck when the tires are cold. ^[NHTSA]

Part 5: Why it’s worth the five minutes

Only 19 percent of consumers properly inflate their tires, according to NHTSA, and correct inflation can extend average tire life by 4,700 miles. ^[NHTSA] FuelEconomy.gov adds that proper inflation improves gas mileage by 0.6% on average and up to 3%, and that mileage drops about 0.2% for every 1 psi drop in average pressure. ^{[FuelEconomy.gov]} Keep a gauge in the car: NHTSA notes a tire can suddenly lose pressure after a pothole or a curb bump. ^[NHTSA]

Bonus: what TPMS can’t see

TPMS watches pressure, not tread or age. NHTSA says to stop using a tire if its tread is worn to the minimum, it shows cuts, cracks or bulges, or it wears irregularly from underinflation or overloading, and to see a tire professional for performance changes such as noise or vibration. ^[NHTSA]

Calm next steps

1. Find your door-edge label and note the recommended cold pressure.
2. Buy an inexpensive tire gauge and keep it in the glove box.
3. When the light comes on, check all four tires and the spare.
4. Inflate to the label pressure, not the sidewall number.
5. If the light flashes for a minute and then stays on, book a TPMS inspection.

Frequently asked questions

Does my car have TPMS?

All passenger cars, light trucks and vans from model year 2008 or newer are required to have it; some 2006 and 2007 models do too. ^[NHTSA]

Why does my tire light come on in the morning and go off later?

Likely marginally low pressure that dips below the threshold overnight and rises as the tires warm. Check your pressure. ^[NHTSA]

What does a flashing TPMS light mean?

Flashing for 60 to 90 seconds and then staying on indicates a system malfunction; NHTSA says to contact your dealer for an inspection. ^[NHTSA]

If I have TPMS, do I still need a gauge?

Yes. TPMS warns only when a tire is significantly underinflated and isn’t a substitute for monthly checks. ^[NHTSA]

Related reading

• Lesson: How Air Bags Work
• Lesson: How Hybrid Cars Save Fuel
• Lesson: Reading Tire Grades (UTQG)
• Lesson: Why Cars Use More Fuel in Cold Weather
• Ask a question

Sources

1. https://www.nhtsa.gov/equipment/tires
2. https://www.nhtsa.gov/winter-driving-tips
3. https://www.fueleconomy.gov/feg/maintain.jsp
4. https://www.nhtsa.gov/summer-driving-tips
5. https://scripps.ucsd.edu/news/voyager-can-may-gray-be-predicted
6. https://www.weather.gov/media/wrh/online_publications/TMs/TM-277.pdf

General education, not a diagnosis. See our disclaimer.