O2 sensor code

[crodrc51]

Check engine lite came on. Checked the code with my Diablosport and it is the front passenger sensor. I cleared the code with the Diablosport, and the check engine lite has not come back on. Does this mean that everything is kosher, or is the sensor still bad and needs to be changed? Car has 40,000 miles, is an '03 and has a no cat x pipe. The rear 02 sensors were shut off so no engine lite would go off. Do I need to change all 4 if I change the sensors or do I need to jsut do the front 2?
Thanks for all responses.