Don’t just check your tires, check your tire gauge

Lately the dramatic weather and temperature changes have caused my low tire pressure (TPMS) light on my car to come on every few days.

Even though I stop and check the tires, and adjust them all to the correct tire pressure, the light doesn’t always go off right away, or it will go off and then come back on shortly after. I actually thought I had a malfunctioning sensor for a while, because I would double-check the air in all the tires, then start driving and the light would stay on.

Yesterday I stopped and thought like a technician: If I readjust the tire pressure and the TPMS light is still on, one of two things are happening: Either my tire gauge is wrong, or the TPMS sensor is bad. Tire gauges are cheap, so eliminate that first.

I use one of those stick-type tire pressure gauges to check my tire pressure, the kind you find at the gas station for about $5 or so. I went to Wal-Mart and picked up a digital pressure gauge for about $6. Then I checked a single tire using both gauges, twice, alternating gauges.

The result was clear: My gauge was off.

the “stick” tire pressure gauge consistently measured 3-4 PSI higher than the digital gauge. I re-inflated the tires according to the digital gauge and the light went off immediately. The tires were actually properly inflated now. Since I already suspected the gauge was bad, this confirmed it rather quickly, and means that I was short 3-4 PSI per tire when I thought they were properly inflated. That’s why the TPMS light was always coming on — the tires weren’t actually properly inflated. Rather, they were a few pounds short.

The gauges are cheap enough, you’re probably good to buy a new one between summer and winter and re-check your tires, especially if your TPMS light is on, or you’re having trouble maintaining correct tire pressure — it could just be your gauge.