The sun is shining, and minus a few assholes who insist on going 30mph over the speedlimit, the roads are clear.
It’s shaping up to be a beautiful day to be on the road.
Until you look at your dash and you notice there’s a glowing yellow light. If you’re like me, that’s usually followed by a choice word or two and some underlying anxiety.
While it may not be as serious as your check engine light, seeing your tire pressure light come on should be a cause for at least minor concern. The good news is you should be able to address the problem with a very few simple steps as I’m going to show you in a minute.
So if you’re like me and you’re stressing out, take a deep breath. You’ve got this.
What Does The Tire Pressure Light Look Like?
Before we get into all the nitty-gritty details, let’s make sure we’re on the same page about what the tire pressure light looks like.
The TPMS Sensor (also known as the tire pressure light) is almost always a yellow or orange indicator found on your dashboard. It’s a semi-circle with an exclamation mark in the middle.
There are some older vehicles that may not have this mark. Typically they will have an orange or yellow indicator that says “TPMS”. For 99% of you reading this, your tire pressure light will look like the one I’ve shown you above.
Depending on what type of vehicle you have, it may appear on the speedomter or nearby on the dashboard. Some older models will
If you look at it, it does kind of look like a flat tire, which is ironic considering what you’re about to learn.
The Tire Pressure Light Means That Your Tires MAY Be Underinflated
The purpose of your tire pressure light (TPMS) is to alert you when your tire pressure may be too low for the safe operation of your car. Severely underinflated tires can lead to blowouts or loss of control when driving.
If you’re panicking while reading that, I’m so sorry! That’s the worst-case scenario luckily. Because you’re reading this article I don’t think you’ll ever get to that point.
Generally speaking, the tire pressure light first comes on after a 25% decrease in tire air pressure from the manufacturer’s recommended pressure level. Most car manufacturers have this set at between 30-36 PSI, so that would represent around an 8-10 PSI drop.
By the way, PSI is just the abbreviation for pounds per square inch. 36 PSI would mean 36 pounds of pressure per square inch.
There’s a couple of places you can find your reccomended tire pressure.
You Can Find The Reccomended Tire Pressure On Your Car’s Door (For Newer Models)
You Can Also Find It In Your Owners Manual (For Both Newer / Older Cars)
The TPMS Light Isn’t Always As Accurate As You’d Like, In My Experience
With that being said, in over 20 years of being a mechanic, I can tell you that sometimes it’ll come on with a much smaller drop, sometimes even as little as 4-6 PSI. The F150 I drive is notoriously picky, and the tire pressure light will sometimes come on even when the tire pressure is only 5 PSI underinflated.
I’ve also had plenty of clients who have complained about the same thing, and I’ve read dozens of accounts on forums across the internet of people suffering from the same thing. Your tire pressure light is not gospel, especially for older cars, but that doesn’t mean you should ignore it.
And that’s because…
The Tire Pressure Light Probably Won’t Go Off On It’s Own
As we’ve established, it takes a tire pressure drop of 25% for your tire pressure light to come on.
When the temperature drops, it’s not uncommon for your tires to lose a few PSI. For every 10 degrees fareinheight that the temperature drops, your tires will lose 1 PSI.
Don’t worry; your tires aren’t losing air. The air in your tires does condense as the temperature drops, which causes it to take up less space. For you, this means less tire pressure, even though there’s not less air in the tires.
If there was a major temperature drop during the night (which is most common) and you get into the car in the morning only to notice your TPMS light, drive the car around for 10 minutes or so.
As the tires warm up, the light may go off as the tires warm back up and the air inside them expands.
But you’re not out of the woods yet.
For your tire pressure light to come on, one or more of your tires needs to lose at least 25% of it’s air. With the average tire pressure being between 30-36 PSI, that means your tire needs to drop somewhere between 8-10 PSI for the light to come on.
Considering that a 10 degree drop in temperature is equal to a loss of 1 PSI, it would take a drop in temperature of between 80-100 degrees for the tire pressure warning light to come on.
For reference, the world record cold snap was only a 58-degree drop in a 24 hour period (which you can read more about here).
That 58 degree drop would only be good for a pressure change of 5.8 PSI, which is far below the 8-10 PSI your tires need to lose in order for your TPMS light to come on.
This means if cold weather is causing your tire pressure light to come on, your tires are already underinflated. If this is happening to you, make sure you top them off when you get a chance.
To reiterate: cold weather can cause your tire pressure light to come on, but only if your tires are already underinflated. It’s important to keep your tires inflated to the manufacturer reccomended pressure during the winter, because it is normal to lose a few PSI due to temperature drops.
If Your Tire Pressure Light Comes On While Driving, Don’t Panic. Drive To A Gas Station With An Air Pump.
As we’ve learned so far, when the tire pressure light comes on, one or more of your tires has less air in it than it should. Officially, this is supposed to be when the tire has only 75% of the recommended air.
However, in practice, the threshold can be far lower than this, especially on older vehicles. Which is what leads a lot of people to ask “what do i do if my tire pressure light comes on?”
Well, the good news is that your tires aren’t going to blow up the second your TPMS light comes on. That would suck pretty badly. The TPMS (tire pressure light) is just a warning, not an “oh my god, immiment doom is coming!”.
It’s ignoring your TPMS light and continuing to drive when your tires are underinflated that will do you in, not driving on them for a couple of hours (unless you have a puncture, which we’ll discuss in a minute).
So here’s what I reccomend you do when the light comes on:
- First things first, don’t panic. As mentioned, your tire pressure light is only a warning, not a suggestion of imminent danger.
- When you get a chance, pull over and find a gas station near you that has an air machine. We’ll use this to fix your tires.
- Drive to that gas/service station and pull up to the air machine.
- Depending on the service station the air machine may have a built-in tire pressure gauge. Alternatively, if you have a newer car, your car’s computer may tell you which tire is low. If not, you’ll need to go buy a tire pressure gauge. Nearly all gas stations will sell these in their store. You may even be able to borrow one from the attendant.
- Even if you already know which tire is low, I recommend checking the tire pressure on each of your tires manually. If you’ve never done it before, please watch the video above.
- While checking each tire, you should visually inspect each tire. Look for any small punctures and listen for the sound of hissing air. If you have water, pouring water over the tire can help you identify a slow leak. Check for any nails or bits of glass that may have punctured your tires.
- If you can’t find any issues with the tires, fill them back up to the recommended tire pressure level. Do not overfill them.
- Once you’ve filled each tire, double-check the pressure on each again and confirm it matches the manufacturer’s recommended pressure.
- The tire pressure light should go off. If it doesn’t, you’ll need to reset it. See the section about how to reset it below.
- Pay attention and see if the light comes back on. If it does, see the section below about the next steps.
Once you’re done filling your tires, drive the car back home and then pay attention to what happens afterwards. If the light shuts off, you’re all set! Your tires are in good shape and you’re ready to get back to driving.
Yes, A Full Sized Spare Can Cause Your Low Tire Pressure Light
Did you know that your full sized spare also comes equipped with a tire pressure sensor?
Better yet, if your full sized spare is under-inflated, it can set off your tire pressure light just like a regular tire. Most customers I have in my shop are unaware of this.
Because full sized spares are seldom checked, they are often underinflated due to osmosis, as I talked about earlier. Air naturally will permiate through the rubber over time. It’s important to check your spare every few months just to make sure it’s still inflated correctly so you don’t end up with a flat…and a flat spare.
That always sucks (and I know from experience, I’ve done it too. More than once).
With that said, donut tires do not have TPMS sensors, so if you have a donut on your car and the tire pressure light is on, you can safely rule it out.
If The Tire Pressure Light Is Still On After Filling Your Tires, Do This.
There are two types of TPMS sensors, the direct TPMS sensor, and the indirect TPMS sensor.
Cars that are 2008 or newer have a direct TPMS, which measures the air pressure in each wheel directly, while cars that are older than that have an indirect TPMS, which measures the pressure based on the wheel speed.
For older vehicles, indirect-TPMS doesn’t measure tire pressure directly and instead uses the tire rotation speed to compare wheels and tires to each other. It can do this because tire rotation speed can be mathematically correlated to tire circumference, and tire circumference is directly related to tire radius, which is directly related to tire pressure. Put simply, lower tire pressure results in a “smaller” tire, which spins faster.
By comparing rotation speeds, using wheel speed sensors (WSS), the TPMS module can calculate that tire pressure is low in one or two tires.
Unfortunately, indirect TPMS sensors are generally less accurate, and may stay on even after you’ve refilled your tires.
The first thing to do is to double-check that you’ve filled each tire correctly and that there are no leaks. Once you’ve done that, drive the car for 10 minutes. This can reset the computer and should turn your tire pressure light off after you park and shut off the car.
If it doesn’t, and your light is still on, you’ll want to reset your tire pressure warning light. You may also want to double-check your tire pressure with a different gauge to make sure the readings you got the first time around were correct.
If this still does not fix the issue, and you have a car that’s older than 2008, you’ll need to reset the light manually.
It’s also possible that your tire has a puncture that is continuing to let out air pressure. This can be caused by all kinds of things, including road debris, damaged rims, or even severely worn tires.
How To Reset Tire Pressure Light
If you’ve done everything else I’ve mentioned, as well as tripling checking to make sure the correct amount of air is in your tires, but the tire pressure light is still on, I’ve got you covered.
You need to reset your tire pressure light.
There are several ways to do this.
Reset Your Tire Pressure Light Manually
Without starting your car, turn your key to the on position. If you have a push button start, short press the button twice. All of your electronics should come on, but the car’s engine should not start.
Then, press the TPMS reset button and hold it until the light begins to blink. It should blink anywhere between 3-5 times. After it does, release the button and start the car. The tire pressure monitor reset button is almost always located beneath the steering wheel, but if it isn’t, please refer to your user manual if you’re having trouble finding it.
Once you get the flashes, the TPMS light should shut off.
Just to be safe, drive the car around the block for 5-10 minutes to make sure the light stays off.
Take The Car To A Mechanic
If you’re having issues reseting your tire pressure light, you can also take it in to the mechanic. This is especially useful if your tire pressure light keeps coming back on. Chances are it’s a faulty sensor, as mentioned above.
While it’s completely possible to replace the sensor yourself, normally it’s just easier to take your car to the local mechanic and get it fixed.
Get an OBD-II Reader And Clear The Warning Light
Chances are you won’t be reading this article if you’ve got an OBD-II reader, but on the off chance you are, just follow the steps in this video for an OBD-II relearn. It’s fast and easy.
Why Is My Tire Pressure Light Blinking?
When your tire pressure is low, the tire pressure warning light should come on, and stay on. It’s not normal for it to be flashing on today’s automobiles.
There are two reasons why your TPMS light may be flashing.
Your TPMS Sensor Battery May Be Running Out Of Power
Oftentimes your TPMS will be flashing because of the battery module running out on direct TPMS systems. This is the most common reason your tire pressure sensor is flashing. However, it’s not the only reason.
Your TPMS Sensor/Module May Be Faulty Or Damaged
It’s also possible you have a faulty tire pressure sensor or TMPS module. Tire pressure monitoring systems include sensors that are mounted on the wheels or on valve stems, and the tire pressure sensors can wear out or be damaged by potholes, debris or the weather and need replacing. In addition, the electronics for TPMS can fail.
Check tires to be sure they are safely inflated. Poorly inflated tires can cause damage to your TPMS sensor as well.
Your TPMS Sensor Failed To Intialize
Any time tire pressure is adjusted, or the wheels are removed from the vehicle, TPMS should be reinitialized to set detection thresholds. Otherwise, TPMS may falsely indicate a tire pressure problem where there is none.
Check and adjust tire pressure to be sure there are no actual problems, then perform the initialization procedure, which is usually located in the owner’s manual.
This is common with indirect TPMS systems that are common on vehicles older than 2008, although some direct TPMS sensors may need to be reset as well.
If Your Tire Pressure Light Is Blinking, Go To A Mechanic
Often times I get asked “what happens when you tire pressure light is blinking?”.
To answer that question, nothing happens, per say. Your car doesn’t explode and your tires aren’t about to just up and go flat.
Your tire pressure sensor may stop working, however. Considering how important it is to keep your tires properly inflated, this isn’t good. It’s worth taking your car to the mechanic to get fixed.
Why Do Tires Lose Pressure?
All tires lose air pressure naturally over time, even if there’s no punctures or leaks. Air is able to pass through the structure of the rubber, and it does so at a rate of between 1-3 PSI (pounds per square inch) per month. The rate at which this happens depends on the make and model of the tire. Different combinations of rubber have different rates at which the air escapes.
This process (called osmosis) is normal and will happen no matter what you do, so it’s important to check your tire pressure at least once every month or two. While 2 months of tire air loss may not be that much, improper tire inflation can cause tire cupping that will destroy your tires at the worst, or decrease your gas mileage at the best.
It’s worth it to check them. If you neglect it for 6 months or longer, osmosis can represent a loss of between 6-18 PSI, which is more than enough to trigger your tire pressure light or cause your tire to blow out.
Can Low Tire Pressure Cause Your ABS Light To Come On?
The short answer is yes, low tire pressure can cause your ABS light to come on. The ABS (anti-lock-braking) system is responsible for maintaining contact with the road when braking.
This suggests that you may have low tire pressure in one of your tires. The ABS light may also come on as a result of this for a couple of reasons. Your car is equipped with wheel speed sensors at each of the four wheels which monitor wheel speed while relaying this information constantly to the ABS and traction control system which are controlled by the car’s ECU.
When the ECU senses an abnormal speed given specific conditions, it engages the ABS or traction control as needed to control the vehicle properly and safely. Occasionally, these sensors can fail or become faulty working intermittently sending inaccurate signals to the ECU. When this happens, you may experience the symptoms you have described.
The ABS or traction control system may be inadvertently activated by these false or inaccurate signals. Depending on the signal transmitted from the wheel speed sensors to the ABS system as a result of the change in tire pressure, this may have also caused the ABS light to come on.
Will My Car Fail Inspection If My Tire Pressure Light Is On?
The answer is maybe. It depends on your state. There are 18 states that conduct vehicle safety inspections in the United States. To make your life a bit easier, of those 18 states, 4 of them require your TPMS light to be functioning.
These 4 states are: Hawaii, Rhode Island, Vermont, and West Virginia.
In the other 46 states your TPMS light won’t cause you to fail inspection.