service engine light

I have a 2002 explorer in which my service engine light came on i took it to my mechanic and he changed one of the oxygen sensors the light turned off for about 30 miles then came back on, he has checked the rest of the sensors and they are all still good but everytime its reset it just comes back on after 20 miles every time i cant do an emission test till the light is turned off otherwise they would fail me, is there any other problem that may exist other than an oxygen sensor????

Get the exact code nuber and post it back here. We can help more with the code.

okay now i got the code its a code P0401 EGR flow insufficient
i checked the vacum on the egr valve and cleaned it vacum was good but light still comes on after 20 miles need some HELP !!

okay now i got the code its a code P0401 EGR flow insufficient
i checked the vacum on the egr valve and cleaned it vacum was good but light still comes on after 20 miles need some HELP !!
does your mechanic have a scan tool capable of reading sensor data? if so, checking the voltage on thye DPFEGR sensor is the next step. it should read from .6 to 1.3v at idle. over 4v while cruising, if it doesnt fall within these specs then you have a bad sensor, wiring, or pcm. 99 % of the time, if the EGR valve is functioning properly,then a bad sensor is the problem.have never seen a PCM do this but its possible. the other 1 % is wiring. i have had a few instances when the wiring rubbed through somewhere.also have seen a few instances when excessive back pressure blew a hose off the sensor, causing that DTC. but i would definitely focus my attention on the DPFEGR sensor.

thanks i will have my mechanic check this out this light is just making me crazy!!!!