09 Cayenne 3.6 DFI v6 shows P0674 with no driveability symptoms

[KERNELCLIFF]

My 2009 Cayenne base with 110,000 miles displays CEL and posts a P0674 fuel rail overpressure, implausible value via Durametric.  (Unfortunately the actual vales are not shown by the software for the v6.)    There are no problems with startup, rough idle, loss of power, etc.  Just that annoying CEL.  There seems to be a fair amount of conflicting interpretations of the P0674 on the web, and the absence of symptoms is puzzling.  

 

Before my questions, some history.  About 14 months ago, I had what was diagnosed by a local shop as a failing PCV, requiring replacement of the intake manifold, and while we were in there also premptively did the pressure sensor, high pressure fuel pump and the camshaft plug.  Ouch.  Expensive. And now outside the warranty on the parts.

 

So, my questions:

 

Its hard to believe that the PCV is failing again after only 5k miles, and without the usual symptoms of same.  Why/how would a failing pcv valve cause the overpressure condition anyway??  (BTW, the old hand over the oil filler procedure doesn't affect the idle either).

 

How likely is it to be a bad high pressure sensor, since I had that replaced too?  From what I can find on the electrical characteristics of the sensor it does not seem that a false high reading would result from failure mode.

 

Could it be a fault in the high pressure fuel pump-particularly the internal  pressure relief device?

 

My dilemma is this: 

 

A new sensor is cheap, but the procedure for replacement requires removal of the intake manifold and seems pretty nasty for DIY, or involves a lot of expensive labor charges from a shop. 

 

On the other hand replacement of the high pressure fuel pump looks pretty straightforward, and I can get the part for about $275 and the plastic cam plug for about $60 (really??).

 

I'm not usually one to throw parts at a problem, but in this case, while not exactly cheap, I am inclined to replace the HP fuel pump myself and see if it solves the problem before springing for the cost of labor to have a mechanic throw other parts at it!

 

Any thoughts you gurus out there might have would be most appreciated.

 

[Sigurd]

Did you ever find a solution. I have the same code on my 2008.

 

Sigurd

[JFP in PA]

1 hour ago, Sigurd said:

Did you ever find a solution. I have the same code on my 2008.

 

Sigurd

Welcome to RennTech 

 

The code 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.

 

The sensor itself could be bad, or it could be the high-pressure pump pressure regulator actually causing high pressure.  I would suggest having a dealer test your fuel pressure values before going forward as this requires special test equipment due to the very high-pressure values.

 

The sensor and fuel rail are under the intake manifold, which has to be removed to replace it, but some caution is advised as this system operates at between 580 and 1740 PSIG: