I've had a P401 code since I got my 80 about 3 years ago. EGR valve checked out good but the modulator was found to be bad and replaced shortly after but the CEL came back days later (P401). Around this time one manifold exhaust flange gasket started leaking slightly. Some time later we replaced the VSV as a last ditch effort to cure the P401, and did the exhaust leak. Within days the 401 was back and the second flange started leaking. Thinking the VSV didn't fix the code problem I gave up on it and drove the truck for months until the exhaust noise got too loud and just today replaced the other flange gasket. Now much to my surprise there is no current or pending 401 code in the system! 
Now obviously this pre O2 sensor leak was responsible for the rich running smell I've had for about a year now (Duh) but I didn't know and never heard that this could cause a PO401 "insufficient EGR flow" code. Have I been missing something here?
Oh BTW, the smell is gone now and the truck goes like hell!
Now obviously this pre O2 sensor leak was responsible for the rich running smell I've had for about a year now (Duh) but I didn't know and never heard that this could cause a PO401 "insufficient EGR flow" code. Have I been missing something here?
Oh BTW, the smell is gone now and the truck goes like hell!
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