TPMS stands for Tire Pressure Monitoring System. Federal law requires every car sold in the U.S. since 2008 to have one. The system warns you when a tire is low, which prevents blowouts, saves fuel, and extends tire life. Here's how it works and what to do when it complains.
How TPMS actually works
Two designs exist:
- Direct TPMS — a small battery-powered radio sensor mounted inside each wheel, on the valve stem. Reports actual pressure via radio to your car's computer.
- Indirect TPMS — uses your existing ABS wheel-speed sensors. A low tire spins faster than properly inflated ones; the computer notices and warns you. No sensors inside the wheels.
Most US vehicles 2007+ use direct TPMS. The sensors live inside each wheel and last 5-10 years on their internal batteries.
What the warning light means
- Solid steady light → at least one tire is below the safe pressure threshold (usually 25% under recommended). Check pressures, fill the low one.
- Light comes on for 60-90 seconds at startup, then stays on → same as solid steady. Check pressures.
- Flashing for 60-90 seconds at startup, then stays on → SYSTEM FAULT. A sensor has failed, the receiver is broken, or there's an interference problem.
Why "just air it up" sometimes doesn't fix it
If you topped off all four tires and the light is still on, you have one of these:
- Spare tire (for full-size spares with sensors) is also low — check the spare.
- A sensor died — its battery is dead or it took a hit. Light flashes 60-90 sec then stays solid.
- System needs a relearn — you swapped wheels for snow tires and the new wheels' sensors aren't yet registered to your car.
- Cold morning → tire pressure drops 1 PSI for every 10°F drop. Could go on overnight, off when warm.
Cost to fix
- Air them up — free at any gas station with an air pump.
- Replace ONE failed sensor — typically $60-120 installed including service kit.
- Replace ALL FOUR sensors — usually done if multiple are old, $200-400 installed.
- Relearn procedure — included free when you buy tires from us. Stand-alone: $20-40.
California heads-up
California isn't actively pulling people over for TPMS lights, but it IS a smog-check failure on most newer vehicles. If your light is on and you're due for a smog, fix it first.
What we do at BTW
Plug in the TPMS scan tool, identify the bad sensor, replace it with an OEM-equivalent unit, and program the new sensor's ID into your car's ECU. Light stays off. Most jobs are 30-45 minutes. Walk-ins welcome — call (916) 627-1998.