Ah ok - I'm with you now
From what I can gather there are many different types of EMU interface, OBDII, OBDI, CAM-BUS etc.
Wiki has a very good article here:
http://en.wikipedia.org/wiki/On-board_diagnostics
OBDII is pretty standard across all cars from 2001 onwards - however before that cars tended to have a custom proprietary interface thats subtly different for each model in a manufactures car range and hugely different between manufactures. And the corsa-b is way before 2001. They use OBD-1 or OBD-1.5 depending on what you read.
For vauxhall corsa-b's there are actually two different OBD-I interfaces across the range - for those with the higher power engines that can do the paperclip test etc, for those with the lower power cars that you need the reader for as the pins are not wired the same.
The actual interface itself is a simply a pulse width modulated data bus - all the code reader needs to do is listen to two pins (ground and data) and be aware of the interface protocol to read the live data of the bus. All you are doing is listening into the comms from the EMU to the sensors. If you want to a bit more (read codes, reset learned settings such as ICV or O2 loop) then you need to short a third pin and the EMU will "listen" to what the code reader says and act on it.
This becomes interesting as not every car in the range uses the same pins, and certainly not the same protocol.
Therefore you need a tool that knows what pins to play with and what protocol to use - this is usually controlled in the software.
The best tool to get is therefore one that can listen to many pins (multiplex) and has the software to decode the data (VauxCheck) etc.
I bought this one:
http://cgi.ebay.co.uk/ws/eBayISAPI.dll? ... K:MEWNX:IT
And its very good. It comes with the op-com software (looks exactly like this:
http://www.youtube.com/watch?v=sqrhF_6LDcQ ) and a USB to EMU connector.
It has the advantage that you can not only read and clear fault codes you can ask the EMU to re set up an ICV and re-learn the O2 loop etc.
Not only that but can you record live data - here is a link to a CSV file of me taking my corsa for a very short drive - I think I got it up to about 60mph and got the revs to 5.5k as I wanted to check how the sensors etc behaved so I have a baseline for if it breaks again... It can be downloaded from here (I have removed my vin number and immobilizer details):
http://www.sofi.org.uk/car_data.csv
I would open it in excel (or whatever you use for spread sheets).
The software I got is windows XP 32 bit only. It works fine in a virtual machine though (I use linux).
Well worth the £30.