They will not fix it if you have installed a mod-chip. If you installed one, just forget about getting this repair.
They will still fix it if you took the warranty sticker off. The warranty sticker is not important to this repair since it only voids the warranty when there is one. Since most of the people taking advantage of this have not had a warranty in years. If Sony repaired your PS2 in the past, but the Disk Read Error came back, do not worry, they will still do it again for free, they may even replace it with a new one.
When you call Sony you need to talk to a real person. This is the Sony hotline, so there are a million recordings. Just listen for the option to talk to a Customer Service Representative and select that.
While talking to them, make sure you specifically mention that you are getting a Disc Read Error. Those are the "magic" words, you will not get very far without saying "Disc Read Error." After this they will ask you some questions such as if you have used any devices such as a Gameshark, answer no. They will also ask you if you have used a cleaning device on the game disc, say no. They ask a few more questions but those are the important ones.
Once you get the go ahead for the free repair simply follow the instructions they give you. They will ask you if you want to write down the information or have them email it to you. I suggest having them email it to you since it will have the number that gets you the free repair already written on top and it has all the blank spaces for you to fill in the neccessary information so you will not forget to put anything down.
The repair is free but you will have to pay for the shipping to Sony. However they pay for the shipping on the way back. I would suggest that you purchase insurance, you do not want to loose your PS2 just so you can save a couple of dollars.
Once you have sent them your PS2 you can check on the status of your repair by calling up the number, going to the playstation 2 section, and then selecting the option that lets you check on your repair status. You enter in your telephone number and it will tell you when it is assigned to a technician and after they finish the repair it tells you when it was shipped back to you.
They repair time is generally short.The number also works in Canada, and you can get the free repairs there as well. As for outside the U.S.A. & Canada you will need to call your own local Sony number to find out. The number will be located in your PS2 instructions in the warranty section. You can also find it n the package of any Playstation accessory manufactured by Sony.