All good Jaiman, everyone is ignorant until they ask the question. Especially when we tend to talk in terms you're not used to. Still a hell of a lot I'm ignorant about. So I'll try to explain better.
By "code" we mean error code (or DTC - Diagnostic Trouble Code). By "computer" we're referring to the ECUs (Electronic Control Unit)s. So that covers all the modules, or control boxes. Such as the ECM - Engine Control Module, BCM - Body Control Module, ABS Module etc. So every time one of these control modules notices something wrong with it's system, it will log an error code into memory. Meaning any problem encountered or odd behaviour should have a code stored in memory to tell you what part of the car the error was in. They can be current codes or historic codes (well the VE certainly keeps historic codes). For example, whenever the Check Engine Light comes on, a code is stored showing what caused that light. If the problem is still there (light still on) it will show as a current code, but if you fix the problem (light goes out) the code will show as having been an issue, but is not currently a problem. "Clearing a code" refers to wiping it from memory with a scan tool. When we say "thrown a code", we are referring to the error code logged by the control module that is relevant to the problem. By "pulling codes from the computer" we are talking about reading what the error code is. This is mainly done by using a scan tool on modern cars. Which is "having the car scanned". This covers things like a Tech2 (used by holden) or the cheap OBD2 dongles that can do limited things on cars after 2004 (or 2007 - I always forget) when all car makers agreed to standardised systems so mechanics don't have to buy a new scan tool for every make of car. Older cars, like the VN/VP can have the error codes read by shorting out 2 pins on the diagnostic connector and the check engine light flashes a certain number of times to give the code. But they are a lot less comprehensive. (The VN has 18 possible codes, the VE has hundreds, I guess the VY is somewhere inbetween)
When you say you had your car checked out and scanned, I assume you mean the mechanic connected his scan tool to your car and ran a diagnostic check. It would have shown a code that he (or she) looked up and told them what area the problem was in. Now I went from a very basic VN to a VE, so I don't know much about the codes the VY uses. There are general codes on modern cars with OBD2 (On Board Diagnostic 2) as well as more specific ones for different brands/models. But on the VE at least, I'm pretty sure it wouldn't say "brake switch faulty", but which switch and what the problem is. Such as "switch one signal too low" or voltage to high etc etc. I can only guess that the VY having two switches would give at least a code of which switch and hopefully what also. But I'm not sure. I found a list of 45 error codes, but none mention brakes.
Though the throttle position sensor does also list what is wrong.
So hopefully your mechanic is pretty decent and will help. I'd give them a call and explain that you saw them and was told the brake switch was faulty, but replacing it didn't work and was wondering exactly what code came up and if there was any more info they have for you. With some luck they will get you to come back in to re-scan it for free, or can at least tell you some more info (assuming they took a note of what the code was - check your receipt, they might have written it down on that). If the other brake switch is cheap enough, it might be worth just changing that. Especially since the mechanic did say it was a faulty switch - well if he didn't specify which switch.
As for the ABS sensors, well that's really a bit of a guess on our part. Mainly because that is probably the most common cause of this type of problem. Without knowing exactly what error code was found, we can only guess. On the VE it has a different code for each wheel, so an easy test is to check the code and then clear it and swap two sensors over. If the code changes it is the sensor, if it stays the same it is most likely the wiring. But the VY might not tell you which sensor it is. Again with the caveat that I don't know VYs, you might be able to test the sensors with a multimeter (this worked on my VEs sensors). Simply by testing the resistance across the senors pins, I could see one was stuffed. On the good sensor, I would get a resistance reading in one direction only (swapped the test leads to the opposite pins). On the bad sensor I had a resistance reading no matter which pin had positive or negative test lead on it. Pretty sure that's correct, either way it was very obvious they were testing differently. And see if you can trace the wires back and check any plugs. As Tas said, it can be as simple as a dirty plug (or loose/damaged).
Geez, I hope that makes some kind of sense. I also just noticed you said the traction was off, but didn't mention the ABS being off. Usually they're highly linked and both would be off (they use the same wheel sensors). Surely if the problem is either the brake switch or the sensors the ABS is off and warning you. Anyway, good luck, and hopefully someone with some more knowledge (especially with regard to VYs) can clarify or fix anything I've said that may need it.
