So you get into your car on a cool fall morning and you are greeted with this annoying light that’s supposed to be symbolic of a tire with low air pressure. Sure it looks very cryptic but in reality it is really letting you know that one or more of your tires is low on air or if its flashing (except on Nissans/Infiniti. Nissans/Infiniti will flash if its just for low air) that there is a fault with your Tire Pressure Monitoring System (TPMS) other than low air. This system became mandatory on all vehicles starting in 2008, though some auto manufactures have had a similar system in place for a long time already on there higher end vehicles.
Most of the time it really is just that one or more of your tires are under inflated causing this light to come on. You can find the correct inflation pressure number on your driver door jamb (see next illustration) of most vehicles and I believe it is located there on All vehicles starting in 2008.
Every once in a while you will have the low tire light come on and be flashing. This usually means that there is a system fault. Each wheel on MOST vehicles 2008 on up (even the spare tire on some vehicles) has a TPMS sensor in each wheel (some vehicles don’t and will use wheel speed as an indicator of low tire pressure) and these TPMS sensors have a battery in them with a life span of about 5-7 years. When the battery in one of these sensors gets low or dies completely you will start to get the flashing low tire light (remember Nissan/Infiniti is the exception) or it will simply say “TPMS” on your dashboard, actually some vehicles will say “tire pressure monitoring system fault detected”. If you are unsure if it’s a low tire issue or a system fault just set your tire pressures correctly and the light will go out on its own within a few miles of driving. If all the tire pressures are correct (Don’t forget to check your spare tire too, unless it’s a donut) or a little above (you can not judge this by eye, you will need an accurate gauge) and the light still doesn’t go out after a few miles of driving than you have a system fault and will need to bring it some place competent to resolve your issue. This isn’t a DIY type of job because it requires specialized tools such as a tire changing machine and TPMS sensor cloning tool. Typical cost to replace a failed or failing TPMS sensor is about $100 dollars per wheel give or take a little.
How the system works (Direct TPMS): Each wheel (most cars) as mentioned earlier will have a TPMS sensor that looks like one of these.
the sensors show in the images operate on 315mhz or 433mhz frequencies for all cars. These system is known as “direct TPMS”. These sensors have batteries in them that last about 5-7 years. TPMS sensors can only perform one function and that is to send tire pressure data to the cars TPMS computer along with the sensors identification number. The sensors identification number is how the TPMS computer knows which tire is under inflated. So basically the sensors in the wheels can only send information not receive it. The Sensors in the wheels do not continuously communicate with the TPMS computer Only under certain conditions does the TPMS sensors in the wheels communicate, such as pressure loss, When air pressure drops 25% below the manufacturer’s recommended level. You can also trigger the TPMS sensor in the wheel to communicate with a special TPMS triggering tool.
How the system works (indirect TPMS): works with your car’s Anti lock Braking System’s (ABS) wheel speed sensors. If a tire’s pressure is low, it will roll at a different wheel speed than the other tires. This information is detected by your car’s computer system, which triggers the dashboard indicator light.
The advantage of this system is that there are no costly sensors to fail, so you never have to worry about replacing any TPMS sensors.
The Disadvantage of this system is accuracy, this system can often trigger a fault when there is nothing wrong, usually after a tire rotation or mismatched tires. However there is a user-friendly reset button that usually remedies the false alarm.
You should have a good grasp on how TPMS systems work now and be able to quickly identify if you simply have a low tire or a system fault. One last thing i forgot to mention earlier, some vehicles have 2 different tire pressures for the front and the back (example: fronts may require 32psi and rears 40psi), when getting a tire rotation the system will need to be reset or you may never get that light to go out. The place doing your tire rotation should do this for you as part of the service.
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