Owner’s Manual Trivia: Tire Pressure Monitoring System

So, yes, a concession. Of all the new technologies I gained access to when I upgraded from my 2003 GMC to the 2019 XC90, a tire pressure monitoring system wasn’t the one that most excited me. Glad to have it, sure. But it’s hardly as sexy as, say, Apple CarPlay or Pilot Assist.

All that said, I’m glad to know I’ll be warned if the air pressure gets too low in any of my XC90’s tires. I was surprised, though, to learn from reading the vehicle’s owner’s manual that I have to take some small measure of responsibility to keep the system working properly. Primarily, that means recalibrating it any time I change tires or adjust the air pressure in an existing tire.

It’s probably worth knowing that the TPMS in the XC90 is an indirect system, which means that it doesn’t have any air pressure sensors. Instead, it calculates the pressure in each tire by measuring differences in the rotational speeds of the wheels using the vehicle’s ABS (anti-lock braking system). If a tire’s air pressure is too low, its diameter, and consequently its rotational speed, change, too. (An indirection system can’t show you the exact air pressure in your tires, merely warn you if the pressure is too low.)

Bear in mind that the TPMS will trigger an alert only if a tire is significantly under-inflated. That means it always make sense to periodically check your tires’ air pressure manually. (The owner’s manual recommends monthly.) The alert itself takes the form of a symbol that lights up in the instrument panel. It’s shaped like a “U” with the sides bulging, tire “treads” on the bottom, and an exclamation point inside it.

You can check on the status of the vehicle’s air pressure any time you like by opening the Car Status app in App view, and then tapping “TPMS” to display the status of all four tires. A green tire is good; it indicates that tire is inflated above the low-pressure warning threshold. A yellow tire indicates the air pressure in that tire is too low. If all four tires are yellow, one or more tires is low. If all four tires are gray, it means the TPMS system is going through the recalibration process.

For the system to function properly, it must be recalibrated after tires are changed or the air pressure in any of the tires is adjusted. Fortunately, it’s not very hard to do. To recalibrate the system: 

1.     Switch off the ignition.

2.     Inflate tires to proper pressure. (See placard on the driver’s side B pillar for recommended pressure.)

3.     Start the vehicle. (Turn on the ignition switch to start the engine.)

4.     Open the Car Status app in the App view.

5.     Tap “TPMS.”

6.     Tap “Calibrate.”

7.     Tap “OK” to confirm that all four tires have had their air pressure adjusted properly.

8.     Drive the car to complete the calibration process. Calibration will be completed once the car has been driven above 22 mph.

9.     Stop the car. (Turn off the ignition switch to stop the engine.)

Remember that driving on underinflated tires is always a bad idea. It can negatively affect road noise and handling, and can lead to premature tread wear. And hey, those tires on the XC90 aren’t cheap to replace—especially if you opted for the optional 21” or 22” wheels.