According to the National Highway Transportation Safety Administration, there are approximately 11,000 accidents and 200 deaths each year that can be attributed to tire failure, the majority of which are caused by underinflated tires. To ensure optimal stability, control, handling, and braking performance, your tires must be consistently inflated to the optimal air pressure specified by your vehicle manufacturer.
To ensure this, most newer vehicles are equipped with a tire pressure monitoring system that displays a warning light on your dashboard when a tire is significantly low on air. However, there is a common problem of seeing the low tire pressure light, but the tires are fine.
So what is the reason for this issue and how to fix it? Continue reading to find out. However, before diving into the reasons why the tire pressure light keeps coming on and its solutions, you must first understand the basics of the technology measuring tire pressure inside the car.
Tire Pressure Monitoring System: What is it for?
Car tires must be properly inflated to the optimal air pressure specified by your vehicle manufacturer. Underinflated tires and overinflated tires can impair handling and braking, accelerate the wear of your tires and unevenly, and thus compromise your safety on the roads. Underinflated tires are more problematic and account for the majority of tire-related accidents. Underinflation means more contact with the road surface, leading to rapid heat buildup, which can, in the worst case, completely separate the tread from the wheel and make the vehicle uncontrollable.
You might know that most new vehicles are equipped with a TPMS, which stands for Tire Pressure Monitoring System, which is an electronic unit mounted on the tire rim. Its main function is to generate tire pressure information for the car’s computer system.
Note that such a system turns on a light on your dashboard to warn if a tire’s pressure is significantly lower than the recommended pressure specified by your vehicle manufacturer and does not allow you to check the exact pressure. So, just because the light is not on does not mean your tire pressure has been set correctly. Also note that if your car is from an older model year, it may not be equipped with a tire pressure monitoring system like newer models.
Available in two different technological forms, TPMS can either determine the pressure directly or calculate it indirectly using tire rotation information. When the car starts, the TPMS light normally comes on for a second or two. This indicator often looks like a tire seen from the front with an exclamation point inside. Sometimes it will simply say “TPMS”.
If a tire is underinflated, the dashboard TPMS light comes on. It may flash or stay on. So what causes the TPMS light to come on but the tires are fine?
Often, when the tires are not flat or underinflated, the low pressure light on the dashboard comes on. There are many perfect reasons why this might happen:
Extreme Cold Weather
It is quite common for the low tire pressure light to come on, but the tires are fine problem to occur on very cold winter mornings. Hot air expands, takes up more space, and is less dense, but inside the confined space of a tire, this expansion means increased air pressure. In contrast, cold air becomes denser and takes up less space, so inside a tire, this condensation means a decrease in air pressure.
A car tire may measure 30 PSI at 80-degree temperatures during the day, but early the next morning when the temperature drops to 30 degrees because it is often colder at night, it may return a reading of only 25 PSI.
On days when the temperature varies considerably, say about 40 to 50 degrees F between day and night, your tire pressure can vary by about 3 PSI to 5 PSI. This is why it is quite normal that, on a cold winter morning, your dashboard’s low pressure light comes on, but once you start driving, the tires warm up. The air inside the tire will expand, thus increasing the air pressure and the light will go out. So, you see the low tire pressure light, but the tires are fine.
However, if the light does not go out once the tires are warmed up, you should grab your pressure gauge to measure the exact pressure of your tires and inflate them to the correct optimal pressure level.
Recent Tire Rotation or Replacement
As mentioned earlier, the TPMS is located on the tire rim. So, there is a chance that this electronic unit could be damaged during the tire rotation or replacement process. So, whenever you are going to change a car’s tires, check on the spot for the low tire pressure light but tires are good problem to avoid the hassle of returning to the auto shop later.
Furthermore, you might replace old tires with a different tire that does not have a TPMS like the others, or that does not have the correct TPMS as specified by your car manufacturer. When this happens, it is as if your vehicle needs to go through a relearning process, which can trigger the TPMS light but the tire pressure is good.
In this case, all it takes to turn off the light is to take your vehicle for a relaxed drive at a constant speed for about 10 minutes. If this does not solve the problem, you will probably need to take your car to a mechanic for external recalibration.
Faulty TPMS Sensor
If you have used a pressure gauge and confirmed that all four tires are properly inflated to the optimal level specified by your car manufacturer, but every time you start the car, the pressure light comes on and stays on, it means the TPMS is not working properly. In this case, it is best to consult a mechanic to inspect and possibly replace the TPMS.
Physical sensors are subject to wear and tear over time, especially the seals, gaskets, valve caps, or sensor core. These sensors also run on onboard batteries, which have a limited lifespan of about 5 to 7 years (up to 10 years in the best case). Low battery power and age-related wear can cause the TPMS sensor to malfunction and cause the low tire pressure light, but tires are fine problem.
Another reason for TPMS sensor malfunction is the presence of a substance other than air or nitrogen in the tire, such as tire repair sealants used when fixing a flat tire.
Forgotten Spare Tire
You might have just swapped your spare tire, which has been sitting for a while without attention or care. Not all spare tires are equipped with TPMS, but if it is and the tire pressure in the spare tire is too low, it can trigger the warning light.
Almost all tires gradually lose air pressure over time through the inflation valve, even with a spare tire or if the vehicle is stored and rarely driven. There is a cap, but the role of the valve stem dust cap is to keep dirt out rather than better keeping air in. So, although it is recommended to check your tire pressure at least once a month, it is still a good idea to check your spare tire as well and inflate it to the optimal pressure so that you always have a properly inflated spare tire to swap at any time.
Air Loss Due to Physical Impacts
A sudden loss of air pressure in tires is quite common and can cause the TPMS light to come on even if you just properly inflated your tires a few days ago. The pressure loss is likely caused by driving on very rough terrain or hitting a curb, which can cause the momentary separation of the seal between the tire and the rim, thus letting a small amount of air escape.
Other common reasons for air leaks that can cause the low tire pressure light, but tires are fine problem, include damage to the wheel rim due to physical impacts on the road like flying pebbles or debris, or a faulty tire valve that bleeds air gradually.
Low Tire Pressure Light But Tires Are Fine: How to Fix It
Now that we are well informed about the causes of the low tire pressure light but tires are in good condition, let’s address this issue.
You have the choice to reset the TPMS yourself or seek professional help. But be aware that by law, any auto shop must fix the problem before letting you go. So, in the rare cases where troubleshooting and repair take longer than expected, your car will be held hostage until the issue is resolved.
Locate the Reset Button
Placed inside the glove box (a compartment inside the dashboard), you can easily find it in front of the passenger seat. In case you cannot locate it, find the button with “SET” marked on it or consult the car manual.
Note: The position of this button may vary depending on the car’s make and model.
Press the Reset Button
The next step in the process is to press the located button for three seconds. Once the light flashes three times on the dashboard, it means the TPMS is reset. After that, turn off the engine and restart it after five seconds (from the time the light flashes).
This would solve the problem. But, it is important here to note that the TPMS reset process may vary depending on the car model. Therefore, consult the vehicle manual before proceeding.
However, if the above solution does not work for you, take your car to the nearest mechanic for a thorough inspection.
Sometimes, you can’t do it yourself…
Some vehicles like Subarus do not allow you to reset your TPMS sensors yourself. You will need a special tool, which is only available at auto repair shops, auto parts stores, and tire dealers.
In this case, the TPMS sensor receives a unique identifier that must be registered with the ECU, along with pressure information as well as the position and temperature of the tires at that time. Once you rotate or replace your tire, to fill your tire, one or more of this information changes, which requires the sensor to be recalibrated with the special tool above.