This does sound a bit off... The catalyst is able to oxidize hydrocarbons (unburnt fuel) at about 600 degrees. The air injection pump routes fresh air straight to the cat to aid in speeding up the light off time. once there, the cat stays warm enough to oxidize at all times. The oxygen sensors have heater circuits built in (4 wire vs. the earlier 2 wire O2 sensors, this is why they're referred to as HO2S; Heated O2 Sensors) As for the term "Not Ready" this applies to one of the monitors run by the PCM the Emissions Monitor. EGR flow, O2 sensor operation, catalyst temp are all monitored by the PCM so it can decide whether it will run in Open Loop (ignoring O2 sensor inputs) or Closed Loop (adjusting fuel trim by reading the O2 Sensor input) To change a monitor status from "Not Ready" to "Ready" is as simple as driving as per TRIP guidelines. Once a TRIP is completed (a TRIP is an acronym don't remember what it is right now, but a TRIP is different than a drive cycle) then monitors will have completed and be "ready" unless there is a problem in which a DTC will be stored along with freeze frame data (Mode 6) and if enough key cycles for the individual code (Some are instantaneous, some are 3 key cycles, some are 5, and some are successive key cycles), then a MIL or Check Engine Light will turn on as well.