TPMS system issues? Am i the only one

This is for my recently acquired 2017 CX-9 Signature.

When i first bought the car from the dealer a month ago, it came with a low air tire. The car was certified but even during the test drive, i noticed that the rear passenger tire seemed kind of low air.
I purchased the car, took it home and sure enough the rear tire was at 14 PSI. Very low! I saw a nail on the side of the thread - not repairable. How they missed it - i am not sure.
This whole time, the TPMS light was OFF. No warning on the dash at all. If it was not for my visual inspection, i would have never known.

Luckily, I got the dealer to agree to put a brand new tire the next day and in the mean time, i filled the tire with air, back to spec.
5-10 miles of driving later, i get the TPMS light on, yet the tires is at perfect PSI. I reset the light and continue to drive.
The next morning, the tire is low again....at 20PSI, but i decide to drive it to the dealer as is, since they will be putting a new tire anyway. The TPMS light is OFF the whole 9mi long drive to the dealer. As if one of my tires is not at 20 PSI. Not good. Feels like the TPMS system is useless on this car.

I drop the car at dealer and tell them about this. They take a note. They put a brand new tire, they adjust all tires to 37 psi and give me the car. No TPMS lights on. They say the system functions OK as expected - no issues. Really?

Fast forward to this morning. This is 250 miles after the new tire was installed. My wife takes the car to go an important meeting. On the HWY she get a TPMS light on. She has to exit and pull over. I drive to her location, we check the tires with the tire gauge - all of them are at 40 psi (warm). None of the tires is low. Yet the stupid light is ON. She is late for her meeting. I am pissed off!

Really, Mazda??

My car has only 9k miles. How can such a simple TPMS system be defective and so truly unreliable?

Has anyone here had similar issues with the TPMS? Not sure what i can do at this point, other than carry a tire gauge everywhere, just in case. I can't really count on the tire monitoring system in this car.
I bet the dealer will say that they can't replicate and send me home.

Sorry for the rant, but this is very disappointing coming from an almost new, 2017 model, top of the line car, with only 9k miles on it.

I own 2 Mazdas and have never had any problems with the TPMS systems. Having said that, in general these systems can get wacky on any car. Usually it happens when a sending unit goes bad, though this should be rare on a new car.

TPMS systems work by measuring the difference between a given set point and a current value. When the tire was replaced, the dealer should have reset the TPMS system. I believe your manual has instructions on how to do this yourself by pressing a button on the left side of the dash, but can't confirm not owning your model year.

It sounds like your vehicle has the wrong set point for one tire or is malfunctioning if a reset doesn't fix the issue.

See this thread for related info albeit from a newer model: https://www.mazdas247.com/forum/showthread.php?123862875-How-to-reset-tire-monitoring-system-on-2018-cx9

Thaumaturge said:

It sounds like your vehicle has the wrong set point for one tire or is malfunctioning if a reset doesn't fix the issue.

Click to expand...

This would have been my guess as well. I'm not familiar with Mazda's system as this is my first Mazda, but it's possible that the sensor responsible for that tire needs to be recalibrated or replaced.

I came across this in the online 2018 Owner's Manual (not sure if it's the same for the 2017):
The TPMS malfunction indicator is combined with the low tire pressure telltale. When the system detects a malfunction, the telltale will flash for approximately one minute and then remain continuously illuminated. This sequence will continue upon subsequent vehicle start-ups as long as the malfunction exists. When the malfunction indicator is illuminated, the system may not be able to detect or signal low tire pressure as intended. TPMS malfunctions may occur for a variety of reasons, including the installation of replacement or alternate tires or wheels on the vehicle that prevent the TPMS from functioning properly. Always check the TPMS malfunction telltale after replacing one or more tires or wheels on your vehicle to ensure that the replacement or alternate tires and wheels allow the TPMS to continue to function properly.

http://www.mazda.ca/en/digital-owners-manual/2018/cx-9/contents/05120200.html

Does your TPMS light flash for a minute when you start the car? If so, it's a faulty sensor (that the dealership should have caught). The sensor may also have been damaged due to driving with the air too low, as the sensor is installed on the wheel inside the tire (again, this is for the 2018, not sure if the 2017 is the same).

My 2016 tpms light was on twice few thousand miles apart. Both times were false alarm.

My 2012 CX-9 had one tire that would slowly deflate to the point where the TPMS would go off, pressure was about 27 psi instead of 34. I would inflate and report to dealer at next service. They never did find the problem with that tire. I've just replaced all four of the original tires (just under 60,000 miles) with Firestones, recommended by Discount Tire (I told the sales rep I was leaning toward the OEM or Michelin's, but he suggested that the Firestones were better value for money for the kind of driving I do). Anyway, the TPMS light was on when I picked the car up from Discount Tire, the Mazda manual said the sensors would calibrate within 10 miles, and they did. I am hoping my TPMS issue goes away with the new tires, if not, I may need a new wheel.