Wigwam is correct, the XC40 uses the widespread “iTPMS” or indirect tyre pressure monitoring system (mandatory since 2014). Doesn’t have any sensors, it measures discrepancies in tyre diameter through rolling speed with the ABS sensors. It’s a little misleading since it’s not really a tyre pressure sensor, it’s a “tyre pressure deviation detector”.
Few things with that, from experience and reading into it after having to faff about with it due to multiple punctures.
I’m just here pointing out a few things i didn’t know when we had issues, and they might apply to you here. First, and this sounds nitpicky but is actually important, you’re not really resetting tyre pressure values in the infotainment, you’re storing them. You can store three inflated and one flat tyre, then your car will alarm you once you inflate the fourth one. This has an important implication (hence me mentioning it) – once you “store” the value, the car actually needs to drive for 30-60 minutes (not run, drive) for the system to become active. This is of course because you storing a value doesn’t mean anything to the car without sensors, it needs to drive to make the correlation between the values you stored and wheel speed. I’ll quote wiki on that, since i’m not sure i can rephrase it accurately:
“iTPMS cannot measure or display absolute pressure values; they are relative by nature and have to be reset by the driver once the tires are checked and all pressures adjusted correctly. The reset is normally done either by a physical button or in a menu of the on-board computer. iTPMS are, compared to dTPMS, more sensitive to the influences of different tires and external influences like road surfaces and driving speed or style. The reset procedure,[9] followed by an automatic learning phase of typically 20 to 60 minutes of driving under which the iTPMS learns and stores the reference parameters before it becomes fully active, cancels out many, but not all of these.”
Also, after having a quick check what system is in the XC40, i saw that in the manual they reference that the TPMS in the XC40 actually has a “TPMS system fault indicator”, i’ll quote the manual:
“The car is also equipped with a TPMS system fault indicator, which indicates when the system is not functioning correctly. The TPMS system fault indicator is combined with the indicator symbol for low tyre pressure. When the system detects a fault, the symbol in the driver display will flash for about one minute and then remain illuminated. This procedure will be repeated when the car is started until the fault has been rectified. When the symbol is illuminated, the system’s ability to detect or warn of low tyre pressure may be affected.”
Obviously i can’t say for sure, but i’m not certain there’s something wrong with the system (still worth having it checked because if something’s actually wrong, it could be the ABS sensor). This is btw also why the TPMS didn’t react to Wigwams puncture – low wheel speed, and not enough distance for the system to measure the discrepancy.
It’s the inherent (and known to manufacturers) downside to the system, it’s just considerably cheaper than a dTPMS (direct tpms) system with sensors in each wheel, that accurately measure actual pressure.
Prior: SEAT Ateca Xcellence Lux 1.5 TSI DSG MY19, VW Golf GTE PHEV DSG MY23
Current: Hyundai Ioniq 6 Ultimate
Next: we'll see what's available in 2028.