cmags

Hi there - new to the forum - hoping someone here might be able to help me out. My mom drives an '02 Crown Vic and the CEL has been on for months. She's had it serviced by a couple mechanics repeatedly, and they can't figure out what's going on.

I just had the codes pulled at Autozone - they are:
P1151 which the printout says is "Lack of O2 switches-Bank 2 sensor 1" though I've seen elsewhere on the forum that this actually means "pre-cat O2 sensing lean condition"
P0402 which is "EGR system fault"
and
P0155 which is "HO2S 21 Heater condition (Heated O2 sensor bank 2 sensor 1)"

Now the O2 sensors have all been replaced, as well as the EGR valve, all vacuum lines, and the car's been tuned up. There's nothing wrong with the way it drives, but mom is looking at selling the car and it's hard to convince a buyer to "ignore the CEL" - especially since it will fail inspection because of it.

Just looking for any ideas - maybe something simple the mechanics missed? It all looks related, as if it could be caused by the same issue. Is there a heater element separate from that Bank 2 sensor 1 O2 sensor that may be bad, causing that code and the lean condition because the sensor isn't at temp?

Any help is appreciated. Thanks!