Tuesday/ that #&! tire pressure warning light

I had to rush this morning to get into the morning commute traffic on highway I-680 South to drive down to San Ramon for an 8 am meeting.  Well, I had been in the rental car (it’s a red Toyota Corolla) only a minute when I noticed the tire pressure warning light on the dash was on.   Now what?  And which tire?  The dumb little light does not say, of course.  Better hope there is still enough air in to make it down to San Ramon, I thought. After I stopped in San Ramon and checked out the tires, it looked as if the front tire was underinflated.  So this afternoon before I headed back, I found a gas station. Luckily all California gas stations are required by law to provide free air and water, so it was easy to add some pressure to the two front tires.   That did not take care of the warning light, though.  So there.  Who cares.  Now I drive around, probably with overinflated front tires, and a warning light that still says some tire is underinflated.