996SafariC4S

Hello,

My 2008 957 GTS with 130k miles has a phantom issue where it will start to loose throttle power while driving and shut off.

This only really happens randomly once I have been driving it all day or if I go on the highway for more than 1hr.
I will get a check engine light , some sporadic RPMs and then the car stops. ( see video)
But then I wait 15min with the car off, Check engine light goes away, and car drives fine home for another 1hr...... (WTF)!
I took it into the dealer and they drove it for 30 miles and cant find what's wrong with it.
the one time I plugged in to the car when the engine light was on I got the code " P12A1" (online it says high pressure fuel rail sensor)

Has anyone had a similar experience? is it as easy as replacing that fuel rail sensor?

I would greatly appreciate all the help.

Thank you.

v10rick

A generic code, one that I don't recall anyone posting about on this forum.

• Faulty Fuel Rail Pressure Sensor
• Fuel Rail Pressure Sensor harness is open or shorted
• Fuel Rail Pressure Sensor circuit poor electrical connection

Maybe the HPFP is about to fail.
An expensive part to swap out for troubleshooting.
A scan tool may help with this.

996SafariC4S

I forgot to mentioned the dealer replaced the high pressure fuel pump 3 months ago but the problem existed prior to this.

europorsche914

I’ve had a similar issue, but haven’t been able to track it down yet. I have not had the stalling, but when it rains I sense loosing throttle intermittently. I’ve replaced all of the coils, primary O2’s, crank/cam position sensors with no improvement.. I have never received a check engine light and no codes with piwis..

BobcatBrian

With that code, and a new HPFP, I would begin by checking the fuel pressure when you're having the issue. Do you have any way to log the fuel pressure? You need to verify if it's truly a pressure problem or maybe a wiring/sensor problem instead.

Petza914

Any correlation to it happening when the tank is more than half full or only when half or below. One of the low pressure fuel.pumps may be failing but hasn't completely quit yet.

Shuga

What about the normal fuel pump? Not the high pressure one.

This is a fueling issue.

BamaScoot

Definitely a fueling issue, and one mine used to have. The cayenne has two sides to the gas tank:



And two low pressure pumps. I could be wrong here, but I think one pump pushes get to the engine, and the other pump pushes gas from one tank to the other (the one that feeds the engine). So it could be an issue with either of these low pressure pumps. There's a way to test them by pulling fuses but I can't recall what it is right now, should be easy to look up.

goneloco

I thought I had a fuel pump issue but it turned out that the mass flow sensor plug had some play in it. I would go into limp mode and I could typically get it going again but it got worse and worse till it would not start. Hence the idea one or both of the fuel pumps died. They changed out the plug and she's been working great since. It's an easy check to see if the plug has play in it.

acntrrs

Have a similar issue that appeared for the first time yesterday on a road trip. I pulled over and rested the car, fueled up, and pulled the same code. After starting up no issue for next 40mk til I arrived at the destination

Did you get to the bottom of this?

Tank was less than half full and had been on the road for a few hours climbing a hill at a creep in traffic

2008 CTT

Jfrahm

Despite the loose MAF connection I suspect the OP's issue was fuel pump(s) as they can get sticky when failing but work for a while between getting stuck, dying for good.
Depending on your mileage you might want to replace the low pressure fuel pumps, or at least read up on the procedure to pull fuses to test which pump is dead and to maybe get moving again:
https://rennlist.com/forums/cayenne-...etric-log.html

However given the danger of dying in traffic it's wise IMO to replace the low pressure fuel pumps early or after any symptoms.
-Joel.