How many o2 sensors are needed in a 2001 focus

2, upstream and downstream. one will be before the converter, one will be just aft of it. hope it helps. bank one is before and bank two is after.

DON'T REP THEM ALL UNTIL A PROPER DIAG IS DONE TO DETERMINE WHICH IS BAD OR COULD BE CIRCUIT RELATED

Hi Carleeta, I 100% agree with Greg's Orange Auto! Your best option is to have it properly diagnosed by a quality repair shop. They will be able to determine if the problem is caused by 1 or more of the Oxygen sensors and/or if it is in the oxygen sensor circuit. Anything in the circuit could be causing the problem...it could be a sensor, one of the electrical connectors, a wire, or even the software or hardware in the computer...the only way to tell for sure is to perform the required diagnostic tests. Using a professional shop will save you the headaches of wasting time and money guessing at the correct fix.