Low Tire Pressure Light but Tires Are Fine Issue: How To Fix
According to the National Highway Transportation Safety Administration, there are about 11,000 accidents and 200 deaths each year that can be attributed to tire failure, of which the majority of cases are caused by under-inflated tires. To ensure optimum stability, control, handling, and braking performance, your tires must be consistently inflated to the optimum air pressure specified by your vehicle manufacturer.
To ensure this, most newer vehicles today come with a tire pressure monitoring system that shows a warning light on your dashboard when a tire is significantly low on air. However, there’s a common problem of seeing low tire pressure light but tires are fine.
So what is the reason for this problem and how to fix it? Read on to find out. However, before delving into the reasons for the problem of tire pressure light keeps coming on and its solutions, you must first understand the basics of the technology measuring the tire pressure inside the car.
Tire Pressure Monitoring System: What Does It Do?
Car tires must be correctly inflated to the optimum air pressure specified by your vehicle manufacturer. Both under-inflated tires and over-inflated tires can adversely affect handling and braking, make your tires worn out faster and unevenly, and thus can compromise your safety on the roads.
Under-inflated tires are more problematic, accounting for the majority of tire-related accidents. Under-inflation means more contact with the road surface, which leads to rapid heat buildup, which can in the worst case make the tread separate from the wheel entirely and render the vehicle out of control.
Most new vehicles come with a TPMS, which stands for Tire Pressure Monitoring System. A TPMS is an electronic box fitted on the rim of the tire that generates tire pressure information for the car’s computer system.
When a tire’s pressure is significantly lower than the recommended pressure, the TPMS will illuminate a light on the dashboard. However, it does not allow you to check the exact pressure. So just because the warning light isn’t on doesn’t mean your tire pressure is correct. Additionally, older vehicles may not have a TPMS installed.
There are two types of TPMS with their own pros and cons: direct and indirect. Direct TPMS systems use sensors inside each tire to measure the pressure directly. Indirect TPMS systems use the wheel speed sensors to calculate the pressure indirectly.
When the car starts, the TPMS light will normally illuminate for a second or two to indicate that the system is working. The light may look like a tire with an exclamation point inside it, or it may simply say “TPMS.”
If a tire has low pressure, the dashboard TPMS light will illuminate. It may flash or stay on. So what makes the TPMS light on but tires are fine?
Reasons Behind Low Tire Pressure Light but Tires are Fine
Many times when the tires aren’t flat or under-inflated, the low-pressure light on the dashboard turns on. There are many perfect reasons why this might happen:
Extreme cold weather
It is pretty common for the low tire pressure light but tires are a fine issue 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 dense and takes up less space, so inside a tire, this condensation means decreasing air pressure.
A car tire may measure at 30 PSI at 80-degree temperatures during the day, but early morning the next day, when the temperature drops to 30 degrees as it’s often coldest overnight, it might return a reading of only 25 PSI.
On days with substantial fluctuation in temperature, say around 40 to 50 degrees F between day and night, your tire pressure might vary by about 3 PSI to 5 PSI. This is why it’s pretty normal if on a cold winter morning, you find the low-pressure indicator light on your dashboard illuminating, but once you start driving, the tires will warm up. The air inside the tire will expand, thus increasing the air pressure and the light will shut off. So you see the low tire pressure light but the tires are fine.
However, if the light doesn’t turn off after the tires are warmed up, you should grab your tire pressure gauge to measure the exact pressure of your tires and inflate them to the correct optimum pressure level.
Recent tire rotation or replacement
As discussed earlier, the TPMS is located on the rim of the tire. Thus, there are chances that this electronic box gets damaged during the tire rotation or replacement process. So, whenever you are going for a car’s tire change, do check then and there for the issue of low tire pressure light but tires are fine to avoid the hassle of coming back to the automotive shop later.
Furthermore, you might replace old tires using a different tire that does not have TPMS like the rest or doesn’t have the right TPMS as specified by your automaker. When this happens, it’s like your vehicle has to go through a re-learning process, which can trigger the TPMS light but tire pressure good.
In this case, all it requires to turn off the light is taking your vehicle for a casual drive at a constant speed for 10 minutes or so. If this does not resolve the issue, you would most likely need to take your car to a mechanic for an external recalibration.
Malfunctioning TPMS sensor
If you have used a pressure gauge and confirmed that all four tires are properly inflated to the optimum level specified by your automaker, but every time you start the car, the pressure light turns on and stays lighted, this means the TPMS is not functioning properly. In this case, it’s best to consult a mechanic to inspect and possibly replace the TPMS.
Physical sensors are prone to wear and tear over time, particularly to the gaskets, seals, valve caps, or core of the sensor. 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 cases). Low battery power and age-related wear and tear can cause the TPMS sensor to malfunction and cause the low tire pressure light but tires are a fine issue.
Another reason for malfunctioning TPMS sensors is if there’s any substance other than air or nitrogen in the tire, such as flat-repair sealants used when repairing a tire flat.
Forgotten spare tire
It might be that you just swapped in your spare tire, which has been sitting around for a while without attention and care. Not all spare tires come with TPMS, but if it does, and the tire pressure in the spare is too low, it might trigger the warning light.
Almost all tires lose air pressure gradually over time through the inflation valve, even with a spare or if the vehicle is in storage and rarely driven. There’s a cap, but the role of the valve stem’s dust cap is to keep dirt out instead of better keeping air in. So while it’s recommended that you check your tire pressure at least once a month, it’s always a good idea to check your spare tire as well and inflate it to the optimum pressure so that you will always have a properly inflated spare tire to swap in at any time.
Air loss due to physical impacts
Sudden loss of air pressure in tires is pretty common and might cause the TPMS light to turn on although you just inflated your tires properly a few days ago. Loss of pressure is likely caused by driving on very rough terrains or bumping up against a curb, which can cause the seal between the tire and the wheel rim to separate momentarily, thus letting a small amount of air leak through.
Other common reasons for air leakage which can cause the low tire pressure light but tires are a fine issue include damage to the wheel rim due to physical shocks on the road like flying pebbles or debris, or a faulty tire valve that bleeds air gradually.
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Low Tire Pressure Light but Tires are Fine: How To Fix
Now, that we’re well informed about the causes of low tire pressure light but tires are a fine issue, let’s tackle this problem.
You have the choice of resetting the TPMS yourself or seeking help from a professional. But be aware that by law, any auto shop must resolve the issue before they let you drive away. So in the rare case that the troubleshooting and fixing are more time-consuming than expected, your car will be held hostage until the problem is fixed.
Locate the reset button
Positioned inside the glove box (a compartment inside the dashboard), you can easily find it in front of the passenger’s seat. In case, you can’t locate it, find the button with the “SET” marked on it, or else check the car’s manual.
Note: The position of this button may vary according to the brand and the car’s model.
Press the reset button
The next step in the process is to press the located button for three seconds. Once the light blinks three times on the dashboard, this means the TPMS is reset. After this, turn off the engine and start it again after five seconds (from the time, the light blinks).
This would resolve the issue. But, it is important here to note that the process of resetting the TPMS may vary in accordance with the car model. Therefore, do consult the vehicle’s manual before heading for it.
However, if the above solution doesn’t work out for you or you, take your car to the nearest mechanic for a thorough inspection.
Sometimes You Can’t Do It Yourself …
Some vehicles like Subarus won’t allow you to reset your TPMS sensors on your own. You’ll need a special tool, which is only available at any auto repair shops, car parts stores, and tire dealerships.
In this case, the TPMS sensor is given a unique ID that needs to be registered with the ECU, alongside pressure information as well as tire position and temperature at the time. Once you rotate or replace your tire, to fill your tire, one or more of these pieces of information will change, which requires that sensor be recalibrated with the special tool above.
