Good evening
I am looking for a bit of help. My XC90 low pressure light keeps coming on about once a week. Each time this happens I have stopped and had the tire inspected and the tire is fine and so is the pressure. Any idea what is going on? I think I have indirect TMPS system. This last time the guy took tire off put in water and saw nothing.

 

The newer (post 2015 or so) TPMS systems have the computer check for differences between wheel speeds (ie if a tire is low on pressure, its rolling circumference is smaller than the rest and it spins faster). Things that could cause that are 1) one tire that is worn more/less than the others 2) a wonky wheel speed sensor 3) electrical connectore/wiring issue or fault within the ABS computer Assume you are correctly resetting the warning light - if not sure, it may be worth a dealer visit for a scan.