Nissan Repair: vehicle programming, coolant temperature sensor, nissan altima

Question
QUESTION: Nissan Altima 2.5 s 2006 What is reprogramming? Why is this done? the effect on the parameters of car?

ANSWER: Hi there, I don't see why a reprogramming, e.g, BCM, (Body Control Module) for changing security parameters, it is necessary!
Please be more specific as to what needs to be reprogrammed. Nissan, (and other vehicles) do not come with a reprogramming option for the owners/operators except for entry-alarm code changes.

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QUESTION: reprogramming ecm for p0420 dtc - catalytic operation/efficiency
op code: dx31aa
what is this so called reprogramming and what is it's purpose ?
why is this done and why and how does it effect overall parameters of car, engine and efficiency?

Answer
I'm sorry sir but there is NO option for reprogramming an ECU. If you get trouble code P0420 it's because some components of the exhaust system had failed. Like the CAT itself, the front or rear oxygen sensors, an exhaust leak by the exhaust manifold-pipe- converter or a failed coolant temperature sensor that prevents the engine from going into closed loop operation. Please have a qualified technician have a look at the problem and correct it. After the problem has been corrected, the ECM memory is cleared either by a scanning tool or by disconnecting the battery negative terminal for a minute or so, and the CEL (Check Engine Light), goes off!