Why does the check engine light come on a 2002 ford explorer after you have replaced the erg?
Assuming you mean the egr valve, I would make sure that you have the check engine codes cleared. In addition, are you sure that it was truly the egr valve, and not the DPFE sensor monitoring the valve?
Should the check engine light come on again after the 02 sensor and cam shaft sensores have been replaced in a 1998 ford explorer?
The light that shows an engine symbol is your check engine light . If the light stays on while the engine is running, the OBD II system has detected a possible problem with your emission system. If the light flashes on and off, an engine "miss" has been detected . Have your Explorer scanned for any trouble codes to find and then repair the problem.