My wife's Subaru Outback has a warning light on, but the tires look properly inflated. Does the light go on when temperatures drop and air inside condenses? Or is it below the minimum level even when taking into account the cold weather?
Tire pressure monitors (TPMs) do just that — keep tabs on the air pressure inside your tires — and they can’t tell what the weather is like outside. When the outside temperature drops, tire pressure drops as well, 1 to 2 pounds per square inch for every 10 degrees of air temperature.
TPMs are designed to alert you when the pressure in at least one tire falls 25 percent below a recommended level. Unless you’re experiencing 40- to 50-degree temperature drops in your area, a low-pressure warning indicates that one or more of the tires is underinflated. Cold weather is just pushing them over the 25 percent threshold. We recommend you inflate your tires to the proper levels (see the tire placard on the driver-side doorjamb) and check them with a tire pressure gauge frequently for a few weeks to see if any are losing air. A tire could have a slow leak caused by road damage, incorrect mounting or a bad valve.
Don’t try to judge whether tires are properly inflated just with your eyeballs. Some tires have such narrow sidewalls that it’s hard to spot ones that are underinflated. Also, tires on the front of some vehicles may look underinflated because they bear the weight of the engine and transmission. And don’t wait for your TPM to tell you your tires are low on air. Underinflated tires wear faster, reduce fuel economy and can’t carry as much weight as fully inflated tires. Check them at least monthly with a pressure gauge.
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