I am getting an EGR voltage out of range fault code (1400) on a 1999 Taurus
with 3.0L 6 cylindar OHC engine.  The car has around 150,000 miles.

I don't know if it is the EGR sensor or the EGR valve, but both parts are
pretty expensive.  Also, it could be carbon build up from what I
understand, but when I took off the hoses leading to the sensor, I did not
notice any.

I figure I can replace both parts cheaper than I can pay someone to
replace one of them.  So the way I see it, it is worth the gamble that I
can guess correctly as to what the problem is.

Anyone with lots of experience who can give me any pointers, or even just
a good educated guess as to what is more likely the root problem?

Also, this fault code has been around for a little more than a year
(almost as long as we had the car) and it seems that I remember it used to
come up as a fault code 401.  However, now only fault code 1400 comes up
after having cleared it before.