mhariush

The design is different on the 957 V6, the membrane is in the valve cover. There's no black cap outside the engine.

Libast

Got ya. Apologies for assuming V8 was in play.

jonasyeo

Did you find out what was causing your P12A2 CEL?
I am facing the same issue since Sep 2019. Valve cover was replaced 1 year ago, replace the rail fuel sensor last week, but the P12A2 CEL is still ON.
Noticed the Brake Booster Vacuum Hose is crack and leaking, will be replacing that this week once receive the part (95535557941). Not sure if that is the culprit.

Update: 27 Oct 2019:
Replaced (95535557941). No more CEL and fault code.
Seem like my 2009 V6 cayenne P12A2 was due to split/cracks on the join of that hose.
Engine running smooth, no more rpm bouncing up and down.

Jesus Dominguez

Check for a vacuum leak at evap hoses

Mark7000

oil air separator diaphragm
----------
Mine went out at around 98k. I think the dealer charged about $1800, but I still had the GEICO mechanical coverage which cost me a $100 deduct. They also did a per-emptive change of a couple of the hoses in the back of the engine area.

bmills

Ok, at this point I am stumped. I am getting the same 'P12A2' error on my '08 Cayenne V6 with around 50k miles. Based on the service manual information above, I have already replaced the cracking brake booster vacuum lines, high pressure fuel pump, fuel pressure sensor, fuel pressure relief valve, new gas cap, the PCV, valve cover gasket, and intake manifold gasket, and new plugs and lower injectors while I was going through the trouble. The car seems to run fine, with no obvious symptoms. For the most part, it is only ever throwing the 'P12A2' code, but is occasionally accompanied by a 'P0442' code for a very small leak detected in the EVAP system. Do you think it could be a faulty tank vent? Or any other suggestions? If so, can anyone locate a part number or location?

bmills

Ok, I was able to grab some freeze frame data:DTC that caused required freeze frame data storage

P12A2

Fuel system 1 status

CL

Fuel system 2 status

CL

Calculated LOAD Value

18.8%

Engine Coolant Temperature

69°C

Short Term Fuel Trim - Bank 1

5.5%

Long Term Fuel Trim - Bank 1

5.5%

Short Term Fuel Trim - Bank 2

7.8%

Long Term Fuel Trim - Bank 2

6.3%

Engine RPM

681/min

Vehicle Speed

5 km/h

Ignition Timing Advance for #1 Cylinder

14.0°

Intake Air Temperature

1°C

Air Flow Rate from Mass Air Flow Sensor

4.30 g/s

Absolute Throttle Position

12.5%

Time Since Engine Start

471 sec.

Fuel Rail Pressure

3460 kPa

Commanded Evaporative Purge

0.0%

Barometric Pressure

99 kPa

Control module voltage

14.182 V

Absolute Load Value

16.9%

Fuel/Air Commanded Equivalence Ratio

0.925

Relative Throttle Position

1.2%

Ambient air temperature

-2°C

Absolute Throttle Position B

12.5%

Accelerator Pedal Position D

14.5%

Accelerator Pedal Position E

7.1%

Commanded Throttle Actuator Control

2.0%

Long Term Sec. O2 Sensor Fuel Trim - B1

0.0%

Long Term Sec. O2 Sensor Fuel Trim - B2

0.8%

aka2465

I’ve been plagued by the P12A2 code for the last few months even though the car runs fine. First I had a shop replace the fuel pressure sensor. The code went away for a few days then came back. So I replaced the fuel pressure relieve valve, but the code was still there. I then replaced both low pressure fuel pumps in the tank along with the fuel filter and fuel regulator. The code remained, so I replaced the high pressure fuel pump. Still the dang code remained. So then I replaced the fuel pressure sensor that the shop had originally replaced. Finally that cleared the code for good. My 2008 Cayenne base has 196,000 on it, so I wasn’t too upset about replacing parts that may not have needed replacing.

mikefirefox

Great news! I have the exact same problem on the same '08 Cayenne base.
Is the fuel pressure sensor you replaced the same as the Fuel Rail Pressure Sensor that my scanner picks up?

aka2465

Yes, same thing. Here's a video I made:

2009 Cayenne

Did you have to bleed the fuel line once you changed the sensor? I noticed the pressure relief valve changed from flush to going inward when I changed mine.

aka2465

I did not need to bleed the fuel line.