A study by AAA finds in-vehicle tire pressure monitoring systems are generally accurate, but to be certain, motorists should still check their tire pressure manually. Tires are the only part of the car that come in contact with the road, and proper inflation is the key to safety and better gas mileage.

“Whether in rain, sleet, snow, or dry conditions, tires are designed to work best when properly inflated,” said Mike Hoshaw, vice president of automotive services, AAA East Central. “Even though AAA research finds that tire pressure monitoring systems work as intended, a tire can be more than 20 percent deflated before it triggers the dashboard warning.”

Using 2022-24 models, AAA engineers evaluated 11 passenger vehicles including sedans, pickups and SUVs, with “direct” TPMS, which uses air pressure sensors mounted in each wheel.

According to the AAA study, the average percentage difference between displayed and actual tire pressure was between 1.2 percent and -1.5 percent, depending on tire location.

Additionally, the amber warning TPMS light illuminated when tires were underinflated to 75 percent of the posted pressure (located on the sticker inside the door jam) for five of 11 test vehicles.

Five of the six remaining test vehicles illuminated the TPMS warning dashboard light when tires were deflated from 70.3 to 72.9 percent of posted pressure, depending on the test vehicle.

Key findings from study

•No significant error in displayed tire pressure readings was noted for any vehicles evaluated within the study.

•The largest percentage difference in reported versus actual tire pressure was 3.3 percent.

•The large pickup truck had a significantly higher posted pressure than other test vehicles.

One vehicle did not illuminate the TPMS warning light even when one of its tires was deflated to only 65 percent of the recommended posted pressure, despite the immediate update of pressure readings in the instrument cluster.

AAA recommendations

AAA urges motorists to use displayed tire pressures in the instrument cluster and keep tires inflated to the vehicle’s posted pressure rather than relying solely on the TPMS light to determine when a tire needs to be reinflated. TPMS lights only illuminate when one or more tires are severely underinflated, so drivers should regularly check the displayed tire pressure at each corner.

In addition, not all vehicle TPMS systems provide pressure readings.

Some systems, especially on older vehicles, only have a warning light if one or more tires are low.

AAA encourages motorists to check their tire pressure monthly (either in the instrument cluster or using a gauge), even if their TPMS light is not illuminated.

And with winter approaching, it’s important to remember that cold weather makes the air denser, so the pressure in the tire is reduced, triggering a dashboard warning.

Do not ignore the warning even if the light goes off after driving because the tire is likely low.

For this reason, tire pressure should be checked when cold.

Please refer to the full report for methodology details - including specific vehicle makes/models, tire brands and specifications, and testing equipment.

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Editor’s note: AAA East Central is a nonprofit association with 69 local offices in Kentucky, New York, Ohio, Pennsylvania and West Virginia serving 2.7 million members.