Trying to add air to one of my tires

Hey guys my tpms lights came on so I bought one of those tire air compressors that shut off automatically when you get to the correct psi. I filled up 3 of the tires to the correct psi and the machine shut off like it’s suppose to do. Got to the last tire and said it had 25psi so I tried to air the tire to 29psi and the machine kept cutting off. So I thought I had a faulty unit. I returned it and got another one from a different brand and that one did the same thing kept cutting off before I could fill the tire to the correct psi.

So what I did was I Put the machine to 40psi instead of 29psi to see if the air compressor would turn on and it did. Now my question is is something wrong with that tire or the tire stem? Why are the 2 different air compressor machine I got giving me the incorrect psi reading? I hope this made sense.

 

Firstly, I hope the compressor that you got wasn't the kind that plugs into 12 volt outlet, those pull too many amps for the 12 volt outlets and can burn up the thermal link in the back of the socket meaning you will have to rip apart the whole dash to replace the entire socket to get it functioning again if you do burn that up.

If you don't want one hard-mounted and hardwired get the kind with the clamps that clip directly to the battery.

Secondly how are you verifying psi? Are you using an independent digital gauge of good quality? Are all your valve stems the same? Do you have five Tire TPMS and are you possibly overfilling that one tire because you're reading the PSI through the TPMS system from the spare or something and not the tire you're actually trying to fill?

Auto cut off machines are pretty smart and if you had two different units behave the exact same way with the exact same Tire I suspect you do indeed have some issue on your end.

 

Yes it is the 12volt air compressors that I’m using, didn’t know that about them that’s interesting.

Im verifying the psi from the air compressors on the digital screen. Both machines read that I had 25 psi in that one tire but the machines wouldn’t turn on until I had it up to 40psi on the auto shut off. Obviously I stopped before it got to that. I have a 2014 so I don’t think they have a tpms sensor in the spare in that year. I will be buying a hand held regular tire gauge tom though to get a better accurate reading. I think all the valve stems are the same they are all the same tires but not sure. It’s weird when I aired up those 3 tires the tpms went off but I wanted to add more air to that last tire since it was on at 25psi but the machines wouldn’t cut on until I set the psi way higher. Wondering why that is happening with that one tire.

 

I am not a fan of those machines. Get a regular compressor that outputs 90 psi and fill it then check the pressure with a gauge.

 

Me either. I’m too impatient to wait for it to fill the tire.
I still prefer the old style gauge with the slide. Maybe I’m just old school?

 

Yeah I dunno I’ll just buy the little tire pressure gauge and just do it manually.

Those little air compressors are convenient though to take with you on road trips in case of emergencies. Thanks for the reply guys.