Tire pressure sensor

Got in the runner for a road trip and had the tire pressure sensor on. Measured all tires and one 3 lbs low. Filled them all to 35 lbs and light is still on after a 1.5 hour road trip. Is it the spare or a defective sensor?

 

Probably. 3lbs shouldn't be enough to trip it. Drive by any Discount Tire and they will do a free scan to determine if or which one might be defective. Most stock the correct sensors and should be able to switch it out.

 

If you're tire pressures are all good and set within door spec and light still is on,I'd have a shop use tpms scanner and scan the sensors. Sometimes batteries go out/low on sensors causing random infrequent dash light. Or the sensor is just bad itself.

 

It is worth checking the spare tire. This happened on my old 10' FJ Cruiser. All four tires checked good, but the light was still on. So I checked the spare, and sure enough it was very low. Filled it up and the light went off after a few seconds of driving. Years later, I had one sensor go bad and was replaced. So it appears even back in 2010 the spare tire also has a sensor.

 

I've never had one work right. My Nissan Frontier, Xterra, my wife's RAV4 and my 4Runner show(ed) a warning light (before and AFTER a tire change). Had Discount Tire check the sensors=all OK. Had them check tire pressure=all OK. Do it the "old way" (Visual) and double check before each trip and during the trip.

 

I would verify they are all at your desired pressure when cold (includinging spare), then reset the TMPS on the 4runner and see if that fixes your issue.

 

I would've guessed the battery died on one or more, but according to your profile you drive a 2018 so they should still be good IMO. I have a 2013 and I just replaced 3 of them for the first time. I would go to a tire shop and see if they can scan each TPMS sensor.