How does TPMS work?

How tyre pressure monitoring works

There are two types of TPMS system, each using a different method to detect low pressure.

Direct TPMS

Direct systems use a pressure sensor inside each tyre, typically attached to the valve stem or mounted on the wheel rim. These sensors transmit real-time pressure and temperature data wirelessly to your car's dashboard. Direct TPMS is more accurate, typically to within 1 to 2 PSI, and can identify exactly which tyre is low.

Indirect TPMS

Indirect systems use your car's existing ABS wheel speed sensors to detect differences in rotation speed between tyres. An underinflated tyre has a slightly smaller effective diameter and rotates faster than a correctly inflated one. Indirect systems are less precise and may only detect larger pressure changes. They cannot always identify which specific tyre is low.

Important limitation

Both types typically only trigger a warning when pressure is approximately 25 percent or more below the recommended level. By that point, the tyre is already significantly underinflated. This is why TPMS should be treated as a safety backup, not a replacement for regular monthly pressure checks with a gauge.