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Why is My Low Tire Pressure Warning Light On?

If you haven’t run over anything pointy, and if your tires are in good shape, a “low tire pressure warning” light can be a bit of a mystery. While your tire pressure monitoring system (TPMS) is designed to warn your whenever your tires have are 20% or more below  pressure, it’s not always reliable. Since proper tire pressure leads to longer tire life and better fuel economy, it helps to understand why your tire pressure warning light might be on.

Here’s a look at the causes behind your tire warning light and how you can fix it.

Why is my TPMS Light on?

Natural Air Loss and Cold Weather

Tires will naturally lose 1-1.5 pounds of pressure each month, so if you haven’t been checking on them regularly, your warning light is probably on for a good reason. If it’s been five months since you last checked your tires, you could be running 7-8 psi below normal.

Yet changes in temperature can effect tire pressure too – for every 10 degree drop, you’ll loose 1 PSI of tire pressure. This means that if it’s a very cold morning (say 40-50 degrees below the day’s normal temperature), your low tire pressure warning light could be a false-positive…as the temperature increases, your tire pressure will return to normal.

So, if it’s a very cold day – and if you check your pressure regularly – it’s likely safe to ignore your low pressure warning light (only it never hurts to check).

Can Temperature Affect Your Tire Pressure?

Tire Damage

Most drivers shrug off bumping a curb, but damage can compromise the air seal and even the structural integrity of your tire. If your low tire pressure warning light comes on while driving, it’s best to pullover and do a visual inspection. Check for any signs of sagging or deformities in your tires’ shape.

Also look for an “egg” in your tire sidewalls…a tire with a damaged sidewall can fail without warning at any speed above 25 mph. As you can imagine, surprise tire failures at high speeds can be a bit dicey. So check your tires carefully.

Don’t Forget The Spare

If your vehicle has a TPMS, it’s probably monitoring the pressure in your spare tire. Therefore, if you get a low tire pressure warning light, and if you’ve checked all four tires that are touching the ground, than you might need to put some air in the spare.

Beware Too Much Pressure

Recommended tire pressure can be very confusing. There’s a number listed on the inside of your of driver’s door, a number on the sidewall of the tire, and another number in the owner’s manual. In every case, you must ignore the tire pressure listed on the tire and on the sticker inside your door. These pressures are too high for normal vehicle use. At best, inflating to these pressures will make your vehicle ride roughly and make your tires wear prematurely.

At worst, over-inflation can lead to catastrophic tire failure…so read your owner’s manual and inflate accordingly (most vehicles recommend tire pressures between 32 and 35 psi).

Disturbed or Tripped Sensor

If you’ve recently had your vehicle serviced and the tire warning light activated immediately or shortly after, it’s likely that something tripped one or more of the tire pressure sensors. Some models require the TPMS to be reset after adding pressure.

How to Know If You Need to Reset Your TPMS

You May Need to Reset Your Tire Pressure Light

If you’ve checked all your tires (including the spare) and the tire warning light is still illuminated, reset your tire pressure monitoring systems.

Some models require the TPMS to be reset every time pressure is added. Instructions for how to reset your tire warning light vary from model to model. Consult your owner’s manual to find the exact steps.

Remember – under-inflated tires wear out more quickly, are less fuel-efficient, and more likely to cause an accident. Your TPMS is helping to make you safer, but it can’t do all the work. Check your tire pressure monthly for optimal handling, longevity, and fuel economy.

Author Tom Blackman works for Parts.OlatheToyota.com, a website offering genuine Toyota parts at wholesale prices. Be sure to watch Olathe’s “What Do Tire Numbers Mean” video to learn more about your tires.

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6 Comments Post a comment
  1. will #

    The first place to look for the correct air pressure for your specific tires is your vehicle owner’s manual. Correct air pressure should also be listed on the tire placard attached to the vehicle door edge, doorpost, glove box door or fuel door. You may use the manufacturer recommended inflations for standard sized tires on your vehicle.

    December 18, 2012
  2. Mike T #

    Besides saving fuel and money and minimizing emissions, properly inflated tires are safer and less likely to fail at high speeds. Under-inflated tires make for longer stopping distances and will skid longer on wet surfaces. Analysts point to under-inflated tires as a likely cause of many SUV rollover accidents. Properly inflated tires also wear more evenly and will last longer accordingly.

    December 23, 2012
  3. veronica brooks #

    we checked tires with a gauge and have put the proper amount of air in but the tpms light is still on. I have a 2010 nissan maxima sv premium trim, someone that has a maxima says theires was doing the same and she had to put 38 in them and it went off. i would like to know how to reset the tpms. thanx

    May 26, 2013
    • Jason Lancaster #

      veronica – I don’t know the procedure off the top of my head, so I’d suggest checking your owner’s manual.

      May 27, 2013
  4. Ronald Stone #

    Tires are the feet of a vehicle and if you want to keep them healthy, you need to check the tire pressure on a regular basis. Completely agree to Mr. Blackman. I personally keep a check on the tire pressure specially during winters and during long distance journeys.

    June 28, 2013
  5. Mike wilson #

    Get into the habit of checking the tire pressure and adding air as required.
    Both the indirect system (ABS based, light only) on my wife’s 2006 Toyota Sienna
    and the sensor based system (pressure sensor in the valve stem, PSI and
    light) on my 2010 Cobalt require a reset after a tires are rotated or replaced. Also I suggest inflating the tires to the door placard setting (I prefer 2 or 3 psi higher myself) and reset the tire pressure monitoring system (TPMS) using the directions in the Owner’s Manual. It’s better than spending a day at the car dealer for something you could do yourself in 10-15 minutes.

    September 10, 2013

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