Can't fix a stupid P0401 code (EGR insufficient flow)
 

I seem to have the dreaded, chronic P0401 code, insufficient EGR flow, and can't seem to get rid of it. It's on a 1998 Sable, with a 6 cylinder DOHC engine. I'd like to know some of the more obscure tests I might try, since none of the usual remedies have worked for me. I've tried replacing the EGR valve itself, replacing the DPFE sensor, even replacing the darned PCM. I've also removed and thoroughly cleaned the pipe which connects the exhaust to the EGR valve (the one to which the dpfe's hoses are connected). The EGR solenoid seems to open and closes okay, so I'm kinda at a loss as to what else to check. ANY suggestions would be greatly appreciated

You're on the right track...
 

You seem to know what you're doing, but have you checked your intake manifold vacuum? Other than that, the only other thing I can think of is a plugged catilitic convertor. But, a plugged cat would likely lead to more codes. You could have a bad Electronic Vacuum Regulator (EVR), leaking vacuum lines, or bad wiring. Good luck and let us know what you find.;)

Will do. Thanks for the advice. I'm beginning to suspect a vacuum leak, because when I recently rechecked the codes (I've had this problem forever, and I wanted to be sure there were no new developments) there was something new I hadn't seen before: a P0174 code, which says cylinder bank 2 is reading too lean. Possibly a PCV hose leak? Haven't figured that much out yet, but I'll post when I do

the DPFE sensor you mentioned....is that the same as the EGR pressure sensor? i am suspecting that on my car for the P0401 and P0402 codes since i know it is broken. i have the single cam V-6 in my 2000 sable, so maybe you dont have the same sensor i have. just a thought

Yeah, DPFE actually stands for Differential Pressure Feedback EGR, which is just a long way of saying EGR pressure sensor.