99 Jimmy check engine light

My 99 Jimmy's "service engine soon" light came on almost two weeks ago. The service department at my local chevy dealer said to drive it for a week to see if it reset on its own. One week later, it had not reset and the dealer replaced the air pump. It worked fine for about six days and just came on again. What could be wrong?

when my check engine light came on, autozone used an OBDII scan tool and found the front o2 sensor was not working.....