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P12A2 -- Fuel high pressure implausible
Possible fault causes:

- Tank vent (TEV) mechanically faulty (does not close fully)
- Fuel high pressure sensor faulty
- Fluctuating fuel high pressure, e.g. due to:
- Low pressure fuel circuit
- Pressure relief valve
- Fuel high pressure pump
- Injection valve

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  • 1 year later...

Did you ever figure this one out? I also have a 2008 Cayenne V6 running OK but codes for P12A2. It's not running perfectly - every once in a while at idle the RPM drops about 150-200 and its very slightly rough for about a second. This may be when the CEL gets triggered.


It only takes a couple minutes of city driving to post it as pending then pops up as a CEL after about 20km - always at idle. I have to pass Ontario's check engine light test. The car has been trouble free for 9 years (other than being on its 3rd drive shaft) knock on wood ;) Funny how my 2008 V8 burns more oil than a two stroke motor and it passed the Ontario ETest with flying colours.


From Loren's list, I've already replaced:

-- High pressure sensor 

-- Pressure relief valve

-- High pressure pump

This week I'm going to take a stab at the low pressure pump and filter possibly also the tank vent. A friend with the identical car had the same problem resolved a couple weeks ago by replacing the tank vent. He also had every single part of the fuel system replaced under warranty until Porsche figured out that there was a part sticker stuck in his intake so all his pumps, valves and sensors are newer than mine.

After that, from Loren’s list, I’m left with the injection valve.


I’ve also read that some people have resolved the P12A2 by fixing: ?????

-- vacuum leaks

-- PCV valve

-- fuel pump cam follower?

-- rear main seal


I don’t mind spending money on the fuel system since I hope to keep it a couple more years and 160,000 KM is about the time for a Cayenne’s fuel system to crater. The car has been amazing for years.


Anyone else have experience with this P12A2? I’m sure it must be common if my friend with the same car had it at almost the exact same time. Once after replacing high pressure pump I also had a lean code (not sure which one) also makes me think leak?


Here is the output from my cheap ODB reader:


FuelSys 1   CL  CL  CL
FuelSys 2   CL  CL  CL
Calc Load  14.1 14.1 23.1
ECT©       90 90 85
STFT B1(%) 0.8 3.9 15.6
LTFT B1(%) -5.5 -2.3 1.6
STFT B2(%) -0.8 2.3 17.2
LTFT B2(%) -3.1 0 3.1
RPM 697 682 779
Speed 0 0 0
Spark Adv deg 13.5 13.5 -4.5
IAT C 9 12 12
MAF g/s 3.13 3.05 3.55
TPS% 11.4 11.4 11.8
Run Time sec 1009 465 253
Fuel Pres kPa 3400 3510 3390
Command EVAP 0.00% 0.00% 0.00%
BARO kPa 98 98 98
ECU Volts 14.276 13.923 13.994
Load Value 12.2 12.2 20.0
EQ Ratio 0.999 0.999 0.999
Rel TPS% 0.8 0.8 1.2
Ambient C -2 -3 -4
TPS B% 11 11 11.4
ACC Pedal D% 14.5 14.5 14.5
ACC Pedal E% 7.5 7.5 7.5
Command TAC% 1.2 1.2 2.0
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  • 2 months later...
  • 3 weeks later...

12A2 generally means it needs an oil separator.  On the passenger side on the back of your valve cover there is a small hole about 2-3mm in diameter.  If you feel vacuum at that hole your oil separator has failed and is causing a vacuum leak.

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  • 11 months later...

hello everyone, I'm currently dealing with a P12A2 issue on a 2008 cayenne as well and looking for some further guidance on the issue. ive replaced the fuel pump, tappet and sensor. code still remains. truck runs normal. any extra info or direction would be amazing. thank! 

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I ended up just getting it to pass the E Test and that was good enough for me.


I had both fuel pumps and a fuel pressure sensor replaced. Crazy the PSI these things operate at!

I also recently noticed a small leak near where I had the flex pipe repaired - I think that's also throwing off some errors.


Ill plug it into my Durametric in the next couple days to see if that eliminated the 12A2 and let you know. Once it passed the ETest I never looked back since it has run well for ages. It's so old now Im only keeping it running at this point.


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