My Subaru Crosstrek Hybrid has an impressive array of warning lights that illuminate at startup, and fortunately, most of them go off after a few seconds. Except for one. It’s amber, and it looks like an underlined exclamation mark surrounded by brackets. Brock Bowman, the sales manager at a tire retailer, informed me that the symbol is supposed to resemble a flat tire (OK…) and that it serves as the indicator for the tire pressure monitoring system (TPMS). In other words, it’s the tire pressure light.
I’ve tried to turn the light off, but it won’t, even after verifying that the pressure in all four tires is correct. After researching the issue, I figure it’s probably time to take the car to the shop. Why do most contemporary vehicles have this light? What does it mean when it comes on, and what should you do when it won’t go off? Here’s what to know.
What Is a Tire Pressure Indicator Light?
The tire pressure light is part of the TPMS, and it comes on when the pressure in one or more tires falls below a threshold amount from the recommended pressure, usually between 10 and 25 percent, depending on the vehicle model. For most models (except some Hondas), the sensors that monitor pressure are located on the wheel rims behind the air valve stems, which puts them inside the tires. Besides activating the dashboard light, they can also send an alert to the dealer’s repair network if you subscribe to this service.
What Causes the Light to Turn On?
Bowman explains that the tire pressure light illuminates when the TPMS “detects a significant pressure discrepancy in one or more tires.” Even the spare tire can trigger the system. A tire can lose pressure for any of the following reasons:
- A puncture or slow leak;
- seasonal temperature drops;
- natural loss of pressure over time.
The tire pressure light can also illuminate when you install the spare tire, says Bowman. “Many temporary spares lack TPMS sensors, or if they have one, they might not be properly integrated or inflated to the correct pressure for the main system.” The TPMS can also get confused when you rotate the tires, he continues, and if that isn’t the reason the light went on, it may be because of a malfunctioning sensor. Sensors have batteries, and a dead battery can send incorrect readings or no signal at all.
How To Check Your Tire Pressure
Some vehicles, including my Crosstrek, have an onboard monitoring system that displays the pressure in each tire. Unfortunately, it doesn’t work when the TPMS light is on, which means you have to manually check the pressure in each tire with a pressure gauge.
Using a Gauge
You can use a manual pressure gauge, which resembles a pen light and features a spring-loaded, graduated bar that allows you to read the tire pressure. I prefer, however, to use the gauge on a battery-powered compressor I keep in the car, because the digital display is more accurate. Either way, the procedure is simple:
- Unscrew the valve cap from each tire.
- Engage the head of the gauge with each tire valve in turn. If you’re using a handheld gauge, press the head onto the valve until the scale bar pops out from the other end. If you’re using a compressor, screw the hose onto the valve.
- Check the reading. If you’re using a handheld tester, the pressure corresponds to the last gradation that appears. If you’re using a compressor, the pressure will be displayed on its LED screen. Both readings are typically in PSI.
- Replace the valve cap after making each reading and inflating the tire as needed.
Where To Find Recommended PSI Levels
The manufacturer’s tire pressure recommendations are displayed on a label attached to the chassis inside the driver’s door. Open the door, look down, and you’ll see it. Failing that, you can also find tire pressure specs in the vehicle’s owner’s manual.
- Pro tip: Check the label carefullybecause the recommendations for the front and back tires are often different. For example, on my vehicle, the front tires should be inflated to 36 psi and the rear tires to 35 psi.
Recalibrate the System
If the TPMS was triggered by a drop in tire pressure, it has to reset after you inflate the tires. The tire pressure light will stay on until you do one of the following:
Drive It Off
Bowman advises driving the car for 10 to 20 minutes at speeds above 15 mph. That may be enough to make the light go off.
Use the Reset Button
Some vehicles have a reset button for the TPMS located under the steering column, in the glove box or on the dashboard. If you can’t find it in your vehicle, check the owner’s manual to verify that there is one. After you press it, you may still have to drive the car for a while to make the light go off.
Use the Dashboard Menu
In lieu of a reset button, some vehicles may have a reset function in the infotainment system. Scroll through the menu to find it.
What To Do If Your Light Won’t Go Off
“If the tires are properly inflated and the light remains on, it indicates a system issue,” says Bowman. His advice:
- Inspect for slow leaks: Even a small, non-obvious puncture can cause gradual pressure loss that triggers the light.
- Visit a mechanic or tire shop to assess the TPMS sensors for battery or signal failure or to reprogram or replace faulty sensors.
FAQ
Why is tire pressure important?
Maintaining the correct tire pressure is important for at least three reasons:
- Safety – Properly inflated tires maintain contact with the road at all times, helping prevent skids as well as steering and braking issues.
- Fuel mileage – Your car has to work harder when the tires are underinflated, and it consumes more fuel.
- Tire wear – Tires wear out more quickly when they aren’t inflated properly.
Can I drive with the tire pressure light on?
The tire pressure light is simply a warning indicator and doesn’t affect the car’s operation. If you verify all tires are properly inflated, and the light stays on, it’s safe to continue driving until you have time to bring the car in for service. While it’s on, you can always check the tires the old-fashioned way by getting out of the car and using a pressure gauge.
About the Expert
- Brock Bowman is the Senior Vice President of Business Development at Tires Easy, an online tire retailer.
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