Most newer vehicles have a tire pressure monitoring system, or TPMS. It warns you with a dash light when a tire is low. It is a genuinely useful safety feature, and it is also the most common surprise when someone in Edmonton buys a used set of winter wheels on Marketplace or Kijiji.
Two kinds of TPMS
Direct TPMS uses a small battery-powered sensor inside each wheel, usually built into the valve stem. Each sensor reports its tire's pressure to the car.
Indirect TPMS has no sensors in the wheels. It uses the ABS wheel-speed sensors to notice when one tire spins faster than the others, which happens when it is low. Indirect systems usually need a reset after a swap, but they do not care what wheels you use.
Your owner's manual will tell you which one you have.
How to spot sensors on a used wheel
- Metal valve stems with a nut at the base are often TPMS sensors.
- Rubber snap-in stems can be either, so ask the seller.
- Ask directly: "Do these wheels have TPMS sensors, and did they work on your car?"
If the used set has no sensors
Your car will usually show a TPMS warning light the whole time those wheels are on. The car still drives, but you lose the low-pressure warning, and in some vehicles the light can mask other warnings. You can add sensors to the set, but budget for it.
If the set has sensors from another vehicle
Sensors are not universal. A sensor from a different make, or even a different model year, may use a different frequency or protocol. Some are programmable to suit your car, some are not.
Batteries die
Direct TPMS sensor batteries are sealed in and typically last several years. On an older used set, one or more sensors may be at the end of their life. A dead sensor means a warning light, and the only fix is replacing that sensor.
Relearn after a swap
Many vehicles need a relearn after switching to a different set of sensors, so the car knows which sensor IDs to listen for. Some do it automatically after a short drive, some need a tool or a procedure in the owner's manual.
Ask before you buy
Add these to your seller questions:
- Do the wheels have TPMS sensors?
- What vehicle were they on?
- Did the TPMS light stay off with them installed?
If you are not sure what your vehicle needs, tell us when you book at our garage in Laurel, South Edmonton.