my Chiltons manual says, " the powertrain control module (PCM) must be reset after reconnecting the battery. Start the engine and hold it at 3000 RPM untill the cooling fan comes on, then allow the engine to idle for about 5 minutes with all accesories OFF and with the transmission in park or neutral."

i have disconnected my battery many times and never did this. as far as i know my engine is running normally. what does resetting the PCM do?