Why is My Tire Pressure Light on But My Tires Are Full?

Every so often you may discover that your Tire Pressure Monitoring System (TPMS) will light up, but when you stop to air up and check for leaks, your tires are fine. This can be quite annoying because the tires of your car require proper pressure to operate at the most efficient mileage, and avoid unnecessary wear that can create problems with balance. 

In order to avoid day to day alerts concerning pressure fluctuations due to temperature changes and such, most TPMS warning lights won’t turn on unless the pressure drops below 25% of the required pressure value. But what happens when it is giving you a false signal?

Reasons Why You May Be Getting a False TPMS Signal

There are a few simple reasons why your light may be giving you a warning and not be a major inconvenience. Although in some cases you may need a mechanic to help you get things back in order, you may want to first consider the following:

Cold Weather

car on the road during winter

Even with correct tire pressure, dips into cold weather may trigger the sensor to light up. This is because cold contracts matter which may result in your tire reporting as lower than it should. The weather doesn’t have to be extreme either, simple dips below freezing will often cause the sensor to trigger, especially if the vehicle has been parked for awhile. 

The first time this happens it can be alarming, but once you are used to your vehicle’s reactions to weather, you’ll have a better idea of whether this is related to the cold, or something else. 

What to do

Once you begin to drive, your tires will warm up and expand. The light will generally go off within a few miles. If you get 10 or more miles down the road, you may want to stop to double check the pressure to ensure you don’t truly have a slight leak. 

Faulty TPMS Sensor

Tire pressure sensor and car lights signal.

If your sensor light turns on when you start the vehicle, and then stays on, you could also have a faulty TPMS. Occasionally a sensor may not function as it should, but a mechanic can quickly determine if this is the case, especially if your tire pressure is normal. 

What to do

Check your tire pressure if the sensor light does not turn off, and if it continues to stay on despite having a good tire, you will need to consult with your mechanic. 

Recent Tire Replacement or Rotation

Low section of mechanic fixing car tire at auto repair shop

The TPMS is located on the rim of your tire, and for it to work effectively, it must be set correctly. Although it takes a bit to knock it loose, it can happen, and the most likely culprit is a tire change or tire rotation. Sometimes you might not notice an issue until after you have driven away or within the next few days. 

What to do

Any time you have your tires worked on, you should request the pressure gauges checked to ensure they are doing their job before you drive off. But if you notice within the next few days, be sure to bring it back into the shop and have them take care of the problem.

Spare Tire Has Low Pressure

Cropped image of businessman holding tire for wheel replacement at street .

What a lot of people don’t realize is that the spare tire also has a sensor on it and if the spare gets low, it will also trigger the TPMS. Most spare tires aren’t expected to get low since they are driven on so rarely, but if you do use your spare, before putting it back up, be sure to check the tire for pressure and wear to avoid the hassle later on. 

What to do

If you have evaluated all your tires and they seem fine, your spare may be the culprit. It is worth taking it out and checking to avoid a trip to the mechanics.

Low TPMS Sensor Batteries

Battery low in red sign.

TPMS batteries only last 6 to 10 years, and when they start to weaken, it can interrupt the signal. You may find the sensor light comes on and off more often, or stays on for a few days before turning off. If you suspect this might be a battery issue due to the age of your vehicle, there are a few options to consider. 

What to do

If you’ve ruled out tire pressure issues and weather, and your vehicle is 6 to 10 years old, you can either bring it in for evaluation and a sensor change by a mechanic, check with a local tire repair shop, or you can do it yourself. It usually is more affordable to shop around and order your own sensors, and then look for the best deal to have them installed from a tire repair shop to ensure it is done right the first time. 

Internal Electrical Fault

Closeup view of probes of the multimeter

If the TPMS is evaluated as working properly in a shop, but you still have sensor issues, you may have an internal electrical fault or short circuit. This can keep them from communicating with your dashboard and cause the light to stay on, or be inconsistent in their readings. 

What to do

This will require an evaluation by a mechanic after which they can better determine where the issue is occurring and what can be done. If you have one electrical issue, you might also have problems with other various sensors on the vehicle so it is important to rule out. 


Modern light car mileage (dashboard, milage) isolated on a black background. New display of a modern car. Tire pressure - TSI.

So, as you can see, if your tire pressure light comes on and you have determined your tires are perfectly fine, chances are it is a simple fix that requires a quick evaluation concerning weather, spare tire pressure, and any jolts your rims may have had. 

If your vehicle is aging, you may need to have the sensors replaced due to a worn battery, but with a bit of patience, you can save quite a bit of money if you are willing to take steps to find your own. On the off chance you cannot narrow down the issues, a mechanic can help you find the problem and then you can decide which steps you need to make to remedy the problem. 

Let us know if you have any questions, and, as always, please share!

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