I replaced the battery on my 2001 A4 and I do not have the code with me.

You really need to run the Diagnostic programme to get the fault code in order to pinpoint the faulty part. See here for possible fault -
http://www.audizine.com/forum/showthread.php/104097-B6-A4-1-8T-Engine-Speed-Sensor-%28G28%29-Replacement

reset the CPU program by using a code reader as removing the battery sometimes corrupts the program

You need a repair shop

whatever,change the O2 sensor,then recheck codes.

audi a4 1,8T radio code

Have the alternator checked,it should read at the battery 13.65 volts to 14.25 volts,with the ac on high blower,and the headlights on.If it does not read this range,replace it,have the battery checked,make sure it is good,have it load checked.Also tighten the alternator belt,or replace the tensioner if needed,and the belt.

you have a O2 sensor problem. You say you replaced the o2 sensor, the one in the front , before the converter? thats bank 1 sensor 1 ...I would not think a O2 would cause misfires????

sorry to say, you will need to take it in, it needs to be hooked up to their computer to reset and have it start up poperly. It just like a pc when it crash it will try to start in safe mode until you select "Normal" start up

find the trouble code find out wat code mean,s wat an replace wat is not working the code will tell u wat,s not working hope this help u

There are 3 ways to solve this.
1) call Audi USA and provide them with info on your car and request the code number.
2) If you know someone that knows how to open up the stereo radio system. The code is labeled on the inside.
3) this is a last resort option, the option I had to go through. You can take it to a certified Audi dealership and have them go into the radio system and get the code. However I had to pay $145.00 for this service.
Just know that everytime you disconnect the battery in the engine this is gonna happen so be sure to save your code or provide it to to Audi USA for records.