One of the most commonly misunderstood vehicle warning lights is the tire pressure sensor light. Let’s be honest, it looks more like a boiling cauldron than it does a flat tire…
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But even those who do know what the light means regularly ignore it, or say to themselves “I’ll get to it when I get to it”. The truth is, even 5 PSI less pressure in your tire can cause a blowout.
That’s a pretty serious risk to take on. Especially considering you only have the surface area of 4 pieces of A4 paper between your car and the road. If just one of your tires blows out you could be at risk of a major accident.
So, don’t ignore that pesky little yellow light.
What Is A Tire Pressure Sensor?
A tire pressure sensor is a component of the tire pressure monitoring system (TPMS), which constantly measures the pressure inside your car's tire. It's a small electronic device that transmits information from the wheel to the vehicle's ECU, typically via low frequency radio waves.
Not all vehicles have a TPMS system, however these sensors are mandatory equipment on all vehicles in the United States since 2008.
Most tire pressure sensors are attached to the tire’s valve stem and are battery powered. They are programmed slightly differently in every vehicle, but as a general rule they detect when a tire’s pressure has dropped 25% or more below the recommended pressure. This is considered a dangerously low pressure level, and will trigger a warning light or message on the dash.
How Do Tire Pressure Sensors Work?
There are two types of tire pressure sensors.
The first, called indirect TPMS, doesn’t actually measure the pressure inside the tire itself. Yes, a pressure sensor that doesn’t actually measure pressure…
Indirect TPMS instead uses your car’s ABS system, tapping into the wheel-speed sensor to see if one tire is rotating faster than the others. Underinflated tires have smaller circumferences, which in turn means they have to rotate faster than a properly inflated tire. This difference in rotational speed tells an indirect TPMS system that the pressure might be lower in this tire, triggering the light to come on.
The second type of tire pressure sensor is the direct TPMS. These, by contrast, do actually measure the pressure inside the tire. These systems use a gauge mounted inside the tire valve which sends a signal to your vehicle's computer. This information is then displayed on your dash depending on the type of direct tpms system you have.
Low-line direct TPMS systems simply prompt a low pressure warning light, leaving it up to the driver to determine which tire needs more air.
Hi-line direct TPMS systems display the individual pressure of each tire on the dashboard. This gives you a more in-depth look at the state of the vehicle, telling you which specific tire is low, and by how much. It also generally means you can monitor tire pressure on a regular basis, without even getting out of the car.
| Indirect TPMS | Direct TPMS |
| Relatively inexpensive | Generally more expensive that indirect TPMS sensors |
| Require less maintenance than Direct | Require more maintenance than Indirect |
| Less accurate than Direct | More accurate than Indirect |
| Can become inaccurate if you buy a different size tire or if tires aren’t worn evenly | Not prone to inaccuracies due to size and wear |
| Must be reset after inflating every tire, or after tire rotation | Reset not always required |
| No need for batteries | Batteries generally not serviceable, meaning sensors must be replaced when the battery dies |
| Doesn’t read actual pressure | Can tell you the specific pressure of each tire (hi-line systems) |
Why Are Tire Pressure Sensors So Important?
Tire pressure is one of the least understood components of vehicle maintenance out there. Most people understand that worn tire tread is incredibly dangerous, but low or uneven tire pressure can be just as threatening.
Tires are designed to be operated within a certain pressure range, usually depicted on a plate inside the driver's door sill, and often on the tire itself.
When a tire’s pressure is lower than recommended, even by a little bit, it can become seriously damaged. As the pressure becomes lower, more and more of the tire comes in contact with the road. At a certain point, a section of the tire wall itself starts to run against the road. This part of the tire is very different to the tread area, and as a result can and will wear very quickly.
This poses a significant safety issue for everyone in your vehicle, as driving around with a low pressure tire means a much greater risk of a tire blowout. Though some blowouts (mostly at low speeds) are controllable, extreme blowouts at high speeds can have disastrous consequences.
On a less worrisome level, lower tire pressure means more surface area on the ground. This increases friction and inevitably pushes up your fuel consumption. Another reason to check your tire pressure at least once a month.
What To Do If Your Tire Pressure Light Is On
If your tire pressure light comes on while you’re driving, slow down immediately and find a safe place to pull over and stop.
Though in many cases tire pressure lights are simply a warning that your air is low and needs topping up, it could also very easily mean you’ve just gotten a puncture.
If it is indeed a puncture, then you definitely don’t want to be driving any further, so it’s best to pull over immediately and take a look at each of the tires. If it is a puncture, then you’ll want to put your spare tire on.
If not, then you should head to the nearest gas station and check your tire pressures. If it’s been a while since you last did this, it might just be a case of routine maintenance. In this case, your tire pressure sensor has done its job, and you should take it as a reminder that you need to up your maintenance game. TPMS systems are not a replacement for regular tire pressure checks.
If you find that after a few days the light comes on again, you probably have a slow leak. The best thing to do in this case is head to a local tire shop and get the tire repaired if possible.
There are times though where simply pulling into a gas station and pumping up your tires doesn’t actually turn the light off. Depending on your vehicle, you may need to perform a tire pressure sensor reset, which is typically a button that you press and hold.
If this still doesn’t do the trick and the light is constantly on, it could be a sign that you have a faulty tire pressure sensor. It’s not uncommon for the sensor itself to fail.
Why Do Tire Pressure Sensors Fail?
Tire pressure sensors fail for a number of reasons. The most common of which is age. The batteries inside these pressure sensors generally last around 5-7 years, so it’s not uncommon for tire pressure sensors to fail several times within a vehicle’s life.
This wear and tear can also be influenced by how often and how far the vehicle is driven; more driving means the sensor is communicating with the vehicle’s computer more, causing more drain on the battery.
Some tire pressure sensors have been known to fail as a result of corrosion. This is especially common in certain Toyota models. This can result in valve stems breaking off or cracking, causing the tire to go flat.
Other reasons for failure include wiring faults, issues with keyless entry systems, and TPMS module failure, however these are all far less common faults. More than likely if your tire pressure light is on as a result of a failure somewhere in the TPMS system, it's due to a failed tire pressure sensor.
How Much Do Tire Pressure Sensors Cost?
Just like anything else, this is largely dependent on your vehicle make and model, as well as whether you have a direct or indirect TPMS setup.
Indirect TPMS sensors can cost as little as $25 per tire. If you have an direct TPMS system though, you’re most likely looking at between $50 and $250 per tire.
Depending on your vehicle’s system, some special TPMS tools may be required, so it’s best to go to a tire specialist for a job like this. You’ll also need to factor in any labor costs associated with the repair.
Do I Have To Replace My Sensors When I Get New Tires?
In most cases your tire pressure sensors can be recalibrated when you get the tires replaced. In certain models, especially older vehicles, this recalibration process is so complex that it simply isn’t justified, and replacing the sensors altogether may be the best option.
You should also consider the age of the sensors in making this decision. Just because the sensor hasn’t failed yet, doesn’t mean it isn’t near the end of its life. Just like replacing the batteries in your smoke alarms every three months, you should consider replacing your tire pressure sensors if they are getting close to the end of their life.
The batteries in most pressure sensors are designed to last around 5-7 years, so if your car is getting close to that age then it might be a good time to get them changed, especially if you’re already in the shop getting a new set of tires.
Can Temperature Affect My Tire Pressure Sensors?
Another point in favor of checking your tire pressure regularly is the fact that changes in outside temperature can have a direct effect on the air pressure inside your tires.
If you have an indirect TPMS system then you’re unlikely to see a light on the dash due to this, assuming of course that the pressure changes in all four tires equally.
In the case of a vehicle with a direct TPMS system though, which measures the actual pressure inside your tire, such changes in temperature can very easily trigger a warning light.
A change of 10° F in ambient temperature will affect your tire pressure by about 1 psi. This means that seasonal changes that drop temperatures from 80° F to 30° F can create a difference of 5 psi in tire pressure. Such changes are sure to set off a TPMS warning light.
The best way to get around this? Check your tire pressure regularly. It's recommended that you check your tire pressure monthly, which will easily save you from tire pressure warning lights as a result of ambient temperature changes.
What About Run-Flat Tires?
Many modern vehicles are equipped with run-flat tires, which allow you to continue driving even if you get a puncture.
These tires have either a reinforced sidewall or interior support ring that keeps the tire operational so you can get to the nearest tire repair centre.
As a result though, drivers of vehicles with run-flat tires often can’t feel the effects of a puncture or flat tire. This has made tire pressure measurement vital in these types of vehicles, giving rise to the prevalence of the direct TPMS system over indirect types.
What If My Car Doesn’t Have TPMS?
Many older vehicles don’t have any form of tire pressure measurement. Fortunately, there are a number of aftermarket TPMS systems that can be retrofitted to older vehicles.
Many of these will use your car’s 12v lighter socket to power the TPMS display, as it is much more difficult to retrofit a warning light inside the instrument cluster itself.
Conclusion
Got a tire pressure light that just won’t go away? Chances are you have a faulty tire pressure sensor. Head to your local garage and get it check out straight away, the last thing you want is a blowout.
If it does turn out to be something more sinister, and more costly, then you may consider selling your car for cash. You can sell your car to us and get money for it. Contact us today to get a quote!