2009 Cayenne v6 P0674 Fuel rail pressure sensor - inappropriately high

Question

I have 2009 Cayenne V6 which has a direct fuel injection system with both a low pressure electric fuel pump and a mechanical high pressure fuel pump. I keep getting a CEL (check engine light) that comes and goes. No drivability issues, no power loss although it runs a bit ragged at startup.

The code that comes up consistently with my Durametric is P0674:

P0674:
Fuel rail pressure sensor - inappropriately high - Upper limit value exceeded, test conditions are not-completed, fault is currently active and is not causing a DTC light.

I have replaced the Fuel rail pressure sensor, but unfortunately I don't have an appropriate fuel pressure gauge to measure the actual values. The V6 ECU does not report the fuel pressure like it does on the V8s for some reason so I cannot use the Durametric to get the actual values.

Could a failing HPFP cause a too high pressure condition? I was thinking the nonsensical too high reading had to be an electrical fault of some sort thus the replacement of the sensor. I have not dug into the wiring harness or anything like that yet because it will be a nightmare to get to. Other owners have posted that the check valve in the pump tends to fail (preventing it from building pressure) rather than the mechanical pump itself. Is there a built in relief valve as well? Could that go bad and cause unusually high pressure? Personally I am leaning towards an electrical fault of some sort.

I've been stumped by this for some time but since there was no change in drivability (just the CEL) I have let it linger. Any thoughts?

Answer 1

To begin with there is a high number of fuel pressure pump being replaced unnecessarily due to hard start ups and reduced engine power in some cases it is not the high pressure pump. and in some it is.. Recheck the code of course the Durametric is a Porsche scan tool , but Generic codes are suppose to code first, All manufactuer must comply with the OBD II. where the generic codes are the standard, If you have a P12A2 and there is no fault codes for P0193 or P0192 , this may just point to the pressure relief valve, the problem is that it does not give a ragged cold start up. , it give a reduce power. What surprise me about this code condition for a Porsche, every Porshce tech  owner has the fuel pressure sensor code, they all replace the fuel pressure sensor and still suffer with this code. some turn out to be electrical due to its low voltage. Try to get the generic code that is set, Porsche is very vague with P0674