fancy modern car/tire question

[Kali]

how do those automatic tire pressure warning things work? I have a very slow leak - maybe a lb or two every 3 or 4 days. it causes a warning light to come on and that drives me nuts. now even though the car CAME with some goo and a compressor INSTEAD of a spare (not even a donut) the manual warns that it may cause problem with the little sending unit.

now, having lived on dirt roads with plenty of cactus I have used foam for more or less permanent repairs for decades.

is it going to ruin something if I just put a can of foam in there? I am betting the tire repair guys are not even going to be able to find this thing (and with my luck it is probably in the sidewall anyway) it is that slow.

[benEzra]

1. It depends on the make/model of car.

My car-before-this-one used the antilock braking sensors to count tire revolutions, and if one tire started consistently increasing its rotation rate (which meant the tire was losing diameter, hence had to spin faster) it would give a low pressure warning. Some newer cars may use actual pressure sensors in the wheel and transmit to the CAN bus via a low power radio interface, but I'm not positive.

Aha, an article:

https://en.wikipedia.org/wiki/Tire-pressure_monitoring_system

What kind of car/truck?

[Kali]

2. I think it is the direct type

since the manual says if you use the goo, it may cause issues with the thing.

Kia Soul

[sir pball]

3. Don't use the goo!

Souls use valve stem sensors, run the goo through them and you're out $60 on top of the tire repair.

Haven't the foggiest idea why the car would come with the too, except to inflate (no pun intended) your repair bills…

[Major Nikon]

4. You might be able to find it yourself

Put a few drops of dish soap in a spray bottle and fill it up with water. Spray the tire down and look for bubbles.