I have 2002 bonnie with TIRE PRESSURE MONITORING SYSTEM
Like to know how it works. Where is the sensor?

Thanks

It works off the wheel speed sensors. If the computer senses a wheel rotating slower than the rest of the wheels it interprets it as going flat.

Mine will flag sometimes when driving on gravel roads,but after a reset will be fine.

The indirect tire pressure system our cars have use the antilock brake system sensor for rotation speed of each wheel. A tire that'* low on pressure has an effective rolling diameter that is smaller than a normally-pressured tire. So a tire that starts rotating faster than then others triggers a warning to check tire pressures.

Two different answers. Who'* right!?

If you consider the wheel speed sensors are the sensors the ABS system uses to monitor wheel speed, both answers are correct. The wheel speed sensors in the wheels hubs are an intergral part of the ABS system. Tire pressure in our cars is monitored by wheel speed. A flat tire will be turning faster (not slower) since it will be smaller in diameter than a fully inflated tire. Smaller diameter at the same road speed means it turns faster.

??? you got me thinking that the sensor must be very sensitive.

If the hub bearing is going bad which would cause more friction would not that side be a tick slower thus cause low tire pressure light? just replaced the right hub and the tire light is not coming on all the time anymore.

I'm thinking just a maybe on that theory. First of all, the signal for low tire pressure is the wheel turns faster than the others, not slower. Second, most people don't realize how much difference even 10% loss in air pressure makes on the rolling resistance of a tire. The sensor doesn't have to be too sensitive to pick that up.

On the other hand, the sensor and the bearing are an integrated unit, and you noticed the tire light stopped coming on when you replaced the hub. There may be a relationship.

I understand that an under inflated tire would be smaller than the rest, so therefore should turn faster. BUT, when a tire is under inflated it'* rolling resistance increases dramatically. That would make it turn slower than the rest, not faster.

A soft tire will turn faster than one correctly inflated. The fact that it has more rolling resistance (or a dragging brake or bad bearing) makes no difference. If the wheel was turning slower you would be leaving black lines on the road behind it. The car pulls the wheel along as fast as it needs to turn.
When the TPS light came on in a car I was driving I checked the pressures at the next gas station and found the offending tire was down to 20 psi, the others were at the recommended 32psi.
This was a Hyundai rental car btw but the same would apply to other cars.