Fuel Pressure Sensor and PCM - P-0172

[GregD]

I've been chasing a MIL/CEL issue for a few months now on a friend's 2005 S40. Originally the codes were those associated with a bad fuel pressure sensor (Circuit open/high/low etc., don't have the code #'s anymore). It was pretty clear the sensor was kaput so it was replaced and those codes disappeared. The new sensor is a Bosch sold by NAPA. Since then, however, within minutes of starting after clearing the codes a P0172 (too rich) pops up. Additionally, (it's not my car I don't know if it was a pre-existing condition) within minutes of replacing the sensor the owner's toddler in the back seat remarked that she heard a noise back there. Sure enough, the fuel pump is very noisy on this car as well but, like I said, if it was like that before is anybody's guess. Fuel pressure reads (via Auto-X-Ray scanner) a nearly unvarying 41-43 psi at the rail. No idea what this should be at idle. My thinking is that if the pressure is too high, one can't help but end up with a rich condition. So, could the PCM (pump control module) be damaged by an open-circuited pressure sensor such that now pressure is no longer being properly regulated? This PCM was replaced and relocated under the recall in 2008. I have no experience with this type of fuel system (no return line) and don't know if a PCM failure is an all-or-nothing affair or if you could have a situation where it runs but is no longer modulating the pump output. It might explain why the pump "growls like a hungry dog*", (I always loved that description from an ancient Saab post about a bad FPR on an LH system . Alternatively (and sadly) there is also the possibility of a new but defective pressure sensor.

Any thoughts appreciated and thanks in advance to all.