P401/p402

I got the codes read over the weekend and it showed 401/402 EGR Excessive flow/EGR Insufficent flow. My mechanic believes that it may be the EGR Selonid/sensor, and if the EGR ports were bad, then you should get only one code.\
Any comments?? He done a pressure/vac test and all was well.

Since the codes seem to contradict each other I would question the DPFE. This is the device that measures and reports the EGR flow. They are known to fail. DO a search under DPFE. I have outlined a simple test or use a Haynes manual as I think the procedure is in there as well