The use of anti-lock brake (ABS) wheel speed sensors to indirectly monitor changes in tire pressure through the spectrum of ABS signals, but predominantly relying on tire diameter evaluation (reduced tire pressure results in a smaller and faster rotating tire). These systems require recalibration via vehicle reset procedure whenever adjusting air pressure in a tire/changing tires. These systems do not have dedicated electronic pressure sensors or the service kit components that a direct systems does.
Indirect system
