My tire warning light came on so I checked the pressure on all four tires and they're good. Where should I start checking next? TIA

If all tire pressures are good then I would assume one or more of the TPMS sensors is faulty. How old are they?

It's an '18, so one year older than yours.

If I remember right TPMS sensor batteries (which are part of the sensor) last about 5-7 years. After that they fail to report and the computer turns on the light on the instrument panel.

On the older 4Runners like my 2013 there isn't a display to tell which sensor is bad. So after finding out new sensors and programming aren't exactly cheap; I just ignore the light and check my tires occasionally. Newer 4Runners have a readout of each wheel, so you can tell which one is the culprit - although they will all fail in time; so I would change all 4 if I wanted it to work again for another 5-7 years.

Also on my SR5 there is no sensor on the spare because it has a steel rim and a sensor won't fit. I think the spare is more important because you can't see it easily and Toyota installs them with the valve stem up - so they are a pain to check. So, to me, the TPMS system is more trouble than it's worth!

The sensors on my '04 lasted until '22. Even then only 1 was bad and 1 other was weak (Denso sensors). Cold temps can weaken the batteries. Is the TPMS warning light solid or flashing? Flashing means you have a bad TPMS sensor. If one is bad you want to replace all of them at the same time. At a dealership it's not cheap.

If it's flashing you can find out which one it is. Start with the first tire and let out about 5 lbs. If the flashing stops and the light is solid, that one is working. Air it back to normal and go to the next tire. When you lower the pressure 5 lbs. and it continues to flash, that's the bad sensor.

At a dealership (or tire shop than can read Denso sensors) they can get a reading off each tire for the battery level, pressure and heat. I bought one for myself after having a shop replace all 5 sensors I bought off Amazon. A tire shop can replace with a different brand. I'm not familiar with newer T4R controls. The shop can update the ECU or you might be able to with your owner's manual.

VERY good information, thank you guys.

After what ArthurKotb said, it occurs to me that there may be differences in the sensors in my 2013 SR5 and newer 4Runners and models. I know values can be read on newer vehicles without a reader (like other auto makers have done for years!) and the batteries might last longer too. There are also videos out there where people change their own sensors (by deflating the tire and breaking the bead by the sensor and changing them out). Then they either use an aftermarket tool to program them or get a tire shop to do it.

Sounds like my best option is to go to a nearby discount tire store and just have all four sensors replaced.

When a sensor on my 2004 went out after about 19 years I checked with the Toyota dealership. They wanted an outrageous amount to replace them. I talked to a local tire store and they said their reader couldn't read the Denso sensor or program my ECU. (I think later model T4Rs can upload new sensor info, not sure.) He said he could replace the Denso sensors with a different brand and program the ECU for those.

I bought an Autel MaxiTPMS TS501 reader and 5 Denso sensors off Amazon and paid the tire dealer to install them. I took it home and programmed them myself; easy peasy. I paid $200 for the Autel and $33.60 each for the Denso sensors. I'll see how long they last.

The Autel is handy to locate a low tire. My T4R will only show that one of them is low, so I walk around the tires and check each one with the Autel to spot the low one. It also shows the battery status and tire temperature.

BTW, the tire dealer said if I had bought the tires from him he would have installed them for free.