99 Ranger Check engine light

Hows it going? A little new to this forum, but have a few questions on my 99.
I had some codes taken off the main computer.....
PO401-Insufficient Flow
PO153-Circuit Slow response
I am assuming that the O401 is a problem located near, or around the dpfe/egr, and am still trying to locate this on my 3.0 liter engine. I dont understand the O153 code.
My concern here is that the two are unrelated, and even if I replace the DPFE, (Assuming that this is the problem) my check engine light will stay on, due to the O153 code, and I wont even know if what I did has fixed the problem. Can anyone tell me in more detail what this code means, and where to even begin to try to fix it?
I have also heard that the DPFE can cause different codes to go to the main computer. Is it possible that both codes are from the same malfunctioning problem?
Any help is greatly appreciated.
Frank-O

0153 is for slow upstream 02 on bank 2 - replace the oxegen sensor on the drivers side closest to the engine

I replaced the heated oxygen sensor on the drivers side, closest to the engine, and the light stayed off for about 235 miles, on a trip across Washington state. This morning on my way to work, the light came back on again. I am thinking that the PO153, and PO401 codes are unrelated. The sensor that I replaced should have taken care of the O153.
Does anyone have a suggestion on what to replace for the PO401 code, for insufficient flow from the EGR? I dont know whether to replace the EGR valve and gasket, or the PDFE sensor. Any ideas?
Thanks
Frank-0

Ford has lots of DPFE sensor problems. They cannot handle the exhaust chemicals and temperature. #401 is a very common code. check the harness for electrical shorts/opens, check EGR valve for proper operation/blockage. If those two are okay, then replace the DPFE.

you can check for all problems with one test - find the egr valve - follow the hose back from the valve till it dead ends at another valve - this is the evr valve - there is a cover on the top of the valve that will turn - pop that off (it will be hard to get off) - start the engine and then put your finger over the little nipple under the cover - if the engine bogs down the egr system is working properly and the dpfe is bad - if not you need to look at the egr system more

The p0401 is very common. You need to replace the DPFE. Don't mess with checking the EGR valve.

It's not always a part. On my 97 F150 the lines behind the EGR Valve to the Throttle body were plugged up tight. Cleaned them out code 401 went away.