WOOOOAAA 
Looks like i found someone who thinks exactly same as i do 
So for example i installed Tyre pressure sensor, so can this sensor be connected to OBDII ?
can sensors send data to OBDII and by connecting the receiver to OBDII can that sensor’s data be fetched from the OBDII ?
Probably No. The firmware in the car controlling the OBD2 system must be looking for the signals AND the receiver must be sending the signal over a serial link to the OBD2 comm line in a fashion that the car can read. This isn’t plug and play.
Hmmmmm i see…
sorry for being greeding, m asking alot of questions, but i really wanna get a deep understanding of all of these technical things …
can anyone tell me what components are connected to OBDII ?
i know it is the brain of the vehicle but there is a question in my mind "can OBDII be modded to accept more incoming signals of different sensors and port it to the receiver ?
Virtually every electronic control unit is attached to the OBD2. OBD2 is a communication protocol, not a controller itself. It is much like a USB port on your computer. It is for communication. The OBD2 part is a common set of messages to tell you when something is wrong. A P0420 error code is essentially the same on every car. It makes servicing them easier. Other messages sent on the OBD2 line are different for each manufacturer. A message of acceleration value from the ABS controller to the ECU may be unique to that car. Or a message to lock the doors.
You can add controllers to grab the messages and do something with them but manufacturers do not want you to have source code for the ECU or the ABS or ride control computers. There are all kinds of apps written for Android and Apple that can make dashboards and record data and show engine performance using those messages. A search around the internet will identify them. Some folks have hacked the proprietary messages and applied the brakes and turned the car from a PC or phone.
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There after aftermarket tire pressure monitoring systems you can purchase. They work independently from the OBD and have their own display. You could just tear the display apart and installed into the dash.
Combining the OBD and an Arduino UNO board or some other computer, software code writing and sensors you could display just about anything you wish in any form. Actually it is not rocket science, just a lot of detailed work
It’s possible to drive from New York City to Baltimore via San Antonio but why bother?
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TPMS has virtually nothing to do with OBD2
They’re exclusive of each other
OBDII is not a method of communication, there are dedicated communication lines between the PCM, TCM and the OBDII port but that is not for the other modules to use. The vehicles computers communicate on a BUS system, PCI BUS and CAN BUS are examples.
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BRILLIANT !! Seems like i have attracted some vehicle electronic engineers 
PCM, TCM, PCI BUS, CAN BUS seems to interest me more in this now 
i have previously seem some people hack into CAN BUS remotely and deploying codes wirelessly and take control of it …
i had totally forgotten about arduino and what it can do …