I have a 2000 Hyundai Accent, it's a manual
My check engine light came on 5 days ago, then after 3 days it went off, then came on again today. Using my friends check-engine sensor-thingy, the code said "P1123" I can't find any information on this code, and there was none in the pamphlet that accompanied his handy tool. ALSO recently I've been hearing a screeching noise which stops as soon as I hit the brakes, but starts again when I take my foot off the brakes. Any ideas?

Code P1123 refers to the Fuel Trim Additive Air System being too rich. Bottom line it could be your Fuel pump or ECM.

Go to Hyundai Webtech (http://www.hmaservice.com), (log in, you now need a password), enter your Model and year and then click on the DTC/OBD-II tab, P1123 is listed in the Fuel System section. You might want to also check the TSB tab for any Bulletins.

Hope I was helpful.

TS out