I posted a problem a couple weeks ago concerning my wife's 2004 S-line. When accelerating ,after about half throttle the engine cuts back on power. I bought a diagnostic tool and get the code P1555 charge pressure: value above maximum charge pressure. After clearing the fault code it always comes right back after driving.

I installed a temporary pressure gauge to see what the amount of boost was and typically get 4-5 psi boost under part throttle. If I go 3/4 to full throttle it occasionally spikes to 12-14psi momentarily and I noticed a "chirping/shreiking" type noise when this occurs. It always cuts back to about 1-2 psi then goes to the 4-5psi range.

I don't get any faults from the sensors. But is it possible the charge air pressure sensor G31 could be bad? Or would it be more likely to be the wastegate bypass regulator N75? Or???

Thanks in advance,
Scott

 

Well stock PSI shouldn't spike over 11 psi, so if its hitting around 15psi then i would say the N75 valve is at fault. The chirping noise is probably a faulty DV (diverter valve)
I suppose its possible that the G31 sensor could be bad, but i've never had to replace one before.

 

yea my crappy plastic DV was making a squeeky noise when it went bad pull both off and look inside if there is a discoloration then replace them both while your at it ... something better then stock

 

Thanks for your response. I ordered a N75 solenoid valve and two new 710N diverter valves should hopefully get the N75 tommorrow. You say the stock boost should be around 11 psi. My Bentley manual says it should be 1.55-1.65 bar which is 22-23 PSI? WTF?