The answers I got when I was driving an '01 was the APPS was not covered under the engine warranty, only under the basic vehicle warranty until it expired. I was troubled by that reply the first time I heard it and got out the owner's manual. I don't remember the specifics now but had to accept the fact that it was not once I read the warranty details. Generally speaking, after the basic Dodge platform warranty expires the Cummins engine block and internals plus the turbo are covered under the 100k/5year warranty. Sensors and Dodge parts that make the engine compatible with the platform are not.
I never could figure out why but after I began delivering travel trailers I averaged about 45,000 miles lifespan on each APPS. I could talk dealers into selling them for about $435 and could install them myself in less than 1/2 hour.
I had one fail on I-5 north of Seattle early this year and had to limp it along about 20 miles in the outside lane or on the shoulder of I-5 southbound at idle in third or fourth gear until I got to a designated meeting place. I called a local Seattle area dealer on my cell phone and bought an APPS with my credit card and they delivered it to me in the parts truck. I stopped at the agreed location, removed the bad one, the parts delivery truck brought me the new one, and I was back on the road ten minutes later.
It is frustrating to pay that much money for them but they are very simple and easy to replace. A very weak point on the pre-HPCR 24 valve engine.
Harvey