After searching I am still confused by what I actually need to read error codes. Do I need

a self-diagnosis checker?
Make a self-diagnosis checker?
Just a multimeter?
Nothing, but instead read off the check-engine light?

Any guidance would be greatly appreciated.

 

Do you have an S4? If you do, use this guide for a home-made code puller. http://www.teamfc3s.org/info/article...odes/main.html

 

You did not specify whether your car is an S4 or an S5. The process is different for each. The above post pointed you to the method for reading codes if yours is an S4 car.

If your car is an S5 (seems to be so, S4s do not have a check engine light), then the method is at this link:

http://www.johnr.com/cpucodes.html

In neither case do you need to buy a commercially produced digital code checker.

 

Oh I didn't know they are different.

I have an S5. So if my check engine light goes out and doesn't flash anything, that means the CPU recorded no error, am I correct?

 

Getting the codes

You need to turn the engine off, and remove the key.
Now you need to pop the hood and locate the green "test" connector(s). These connectors are located in the front of the car, near the battery on the driver side, and near the airbox on the passenger side. They are green, and not connected to anything.
Locate the green, SINGLE connector near the battery. It should be close to another green multi-socket connector. Take a jumper wire (anything is fine, old speaker wire, etc.) and cram one end into the single green connector, and ground the other end. (I find the conveniently located (-) battery post usually does the trick)
Get back in the driver's seat, and turn the key to the IGNITION only. DO NOT START THE CAR.
The Check Engine Light should come on (as usual when you hit ignition with no start), and then go out. It will then start flashing the CPU version of Morse Code. (See below for decoding hints.)
Watch carefully. Get the timing down. Note that SEVERAL trouble codes my be reported on. You can leave the key in as long as necessary, the codes will continue to repeat indefinately.
Once you have the code(s), you can remove the key, remove the jumper, and start figuring out what is causing the code(s).
Its THAT simple. If you make repairs and want to "clear" the code - to see if you actually fixed things - you should remove the (-) battery cable for about 30 seconds. Repeat steps 3-7 above BEFORE starting the engine to make sure you cleared the code(s). Then take a test drive and repeat steps 1-7 again to see if your problem is gone.

from fc3spro.com