Interstate freakout

Driving home in our Prius post-Thanksgiving I saw our Tire Pressure Monitoring System light go on. We were on an interstate — yikes! — and had just passed the aftermath of a minor collision, with two cars on the shoulder and debris scattered on the road. I had dodged the debris, but now I wondered if I had run over a shard of something and sprung a leak.

We took the next exit and checked the tires — no obvious problem. We’ve had the TPMS light go on before, after getting the tires rotated, so we tried the TPMS reset trick, restarted the car, hoped, and drove on. But the light stayed on. Crap. We got some air closer to home, where we found that all four tires were slightly under pressure, no doubt because of a sudden drop in temperature (about thirty degrees) in the four days since we had last inflated the tires. And the light stayed on.

Rather than pay to have the tires’ sensors checked (not cheap), we figured we should just get new tires (we’re about halfway there). So we called our dealer, who ordered tires but said that we could cancel if the problem went away. It didn’t: the light stayed on, and on. But yesterday, Elaine got gas, and the light went off, and it was only then that we remembered that we had gotten gas shortly before the light went on. It turns out that uncapping and recapping the Prius gas tank can create the problem, and that uncapping and recapping the gas tank can make the problem go away. To quote a redditor: “Last time I check[ed] it was the gas cap.”

And it’s been the gas cap for us before, setting off not the TPMS light but the Check Engine light. O brave new world, that has such gas caps in’t.