Tire sensors are devices inside of your tire that can measure the PSI inside the tire. Vehicles usually come equipped with 4 separate tire sensors, one for each tire.
The sensors are calibrated to detect a good PSI, and a bad PSI. If a tire’s PSI drops below the sensor’s calibrated level, it sends a message to your vehicle’s computer, which in turn turns on the tire light.
Some tire sensors are mounted in the valve stem, while others are wrapped in a metallic band around the rim. These sensors all do the same thing, which is to constantly report the tire’s PSI to the car’s computer.
The sensors operate through radio frequency, and report the PSI to the car’s computer thousands of times per second. It does this so often, in case there is a quick loss of pressure.
The tire sensor can report a loss in pressure before the driver even notices. The tire sensors are basically a small computer inside each of your tires that are battery operated.
Service TPMS vs Tire Light
There are two separate messages that your tire sensor can display. One is a message indicating that one of the sensors has recognized a low pressure.
This message will usually display a small, orange icon in the dashboard. This is your tire light, and it’s what the tire sensors use to notify the driver there’s an issue with tire pressure.
When a service tire monitor light comes on, this message means something entirely different. Service tire monitor message means there’s an issue with the TPMS as a whole.
And what this message usually means, is one of the batteries in the sensors has died. Tire sensor batteries are lithium ion batteries that last around five years. Over time, they lose their charge and need to be replaced.
When one sensor battery goes, you can expect the other sensor batteries to expire not long after. It’s recommended to replace all sensors when one battery has died, instead of coming back to the shop every time a battery dies.
Replacing all four tires can be pricey, but it’s good to do, otherwise, one sensor can have around four months of battery life left while another has five years.
What else can it mean?
In the rare case that the service tire monitor light comes on, and all the batteries are good, it’s time to start some heavy diagnostics.
One issue I see is that customers will add tire sealant to their tire in order to fix a flat tire. The consistency of some tire sealants is thick, and it’s added through the tire’s valve stem.
The valve stem is integral to some tire sensors, so there’s the possibility the tire sensor can become plugged up with the sealant. This will put the sensors into a varying state, causing the service tire monitor message to display.
Another common cause is if it’s a vehicle that was made with TPMS before they were mandated. Older vehicles require you to calibrate tire sensors each time the tires are rotated.
Calibrating the tires requires a special tool in order to register the sensors in their new position. If the TPMS sees that the front sensor is now in the back, but hasn’t been registered there, this will cause the service tire monitor light to come on.
Some older vehicles that get a tire rotation, but didn’t recalibrate the sensors will display the service tire monitor message.
The other most common reason is when new sensors are replaced, but not properly calibrated with the TPMS tool, it will cause the service tire monitor message to display.
Installing new tire monitors in the tire is pretty straight forward. But registering the new TPMS sensors is a whole different ball game. Some vehicles require you to put the car in ‘relearn’ mode, that requires you to hit a series of buttons in the vehicle.
For example, you may have to turn the ignition on and off three times, hit the brake pedal, then flash the brights. This will put the car in re-learn mode, then you walk around with the TPMS tool and register each sensor with the computer.
The feedback during this process is minimal, so it’s hard to know if you’ve done it correctly. Lot’s of techs will assume they’ve done the process correctly because they followed the steps. But when they start the car, the service tire monitor message is displayed.
Service tire monitor messages technically can mean hundreds of different things. But mostly, it means the lithium ion battery in your vehicle is dead.
It’s the leading cause for the message to be displayed on your dashboard. If you see the message, don’t panic. Some people see the service tire monitor message and think there’s an issue with the tires themselves.
But this isn’t what's causing the message to display. It more than likely just means it's time to replace the sensors since the batteries in them are no longer functional. It’s a simple fix, and takes about an hour to complete.
About The Author
Christopher Sparks has been servicing vehicles since 2012. After completing the automotive studies program at Camden County College, he was awarded an Associates's Degree in Applied Science. His first job was a lube-tech at Jiffy Lube, and is currently an independent B-Technician servicing vehicles for the United States Postal Service. Christopher is ASE certified and loves rebuilding engines.Read more about Christopher Sparks