some system use the abs to measeure each wheel speed to work out if a wheel is flat, ie if a tyre deflats more than any of the others then that tyres circufence is less and turns faster than the rest to keep up.
The system i want to be able to test has a sensor in each wheel and a tx in the wheel arch
the tx sends a lf signal to the sensor and then the sensor sends a rf signal to the main reciever in the middle of the car with all the data ( ie pressure and temp ), each sensor is sent a LF signal one at a time so the module in the car no's what sensor is send the data