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Any help on this would be appreciated. Thanks in advance. This is my first post and I will try to be as specific as I can. SORRY if it seems long. I have a base model cayenne 2004 with 89,000 miles. I have always been good about the upkeep... Just changed oil, oil and air filter 2 days ago. 


For a few months now I have been getting the 4WD system faulty and the PSM failure workshop codes. The codes usually do not come up right away upon starting the car. They pretty much always come up in the middle of a drive at various speeds. I could be on the highway or at city speeds. The codes ALWAYS come up together, which makes me think they could be related? 4WD first and then PSM immediately after. (The 4WD definitely works however. I just moved from Minnesota and drove through the mountains in Denver with the car. I had no issues with the car losing traction. It honestly plowed through the ice and snow like a boss!) The small icon on the dash will also stay lit (a triangle with exclamation point in middle with circle arrow around it.) Next time I go to start the car it is gone. I have not noticed any problems with the car while driving. To me it seems perfectly fine and drives the same the first day I bought it. I looked at the previous forums on this problem but I never saw an actual solution? The guy just gave up and sold it. Other users mentioned it could be the battery. I just had my battery checked and was told it is still good. My FM transmitter also checks the voltage every time I plug it in (basically every time I drive) and always says the voltage is normal.  


I took it to a mechanic and he said it would have to be diagnosed by the Porsche dealership. He told me this because he said he does not want to waste my time and suspect the wrong part to replace if that is not really the issue. He said it is really hard to diagnose these cars without the bench only the dealership has. He did give me the exact codes which I can list later once I grab the paper from the glovebox. So basically, he got the codes for me and gave me some more transmission fluid which he said was a little low. He cleared the codes for me and charged me $75 dollars. Seems stupid considering I still have the issue and now have to go to the dealership next Friday to get proper diagnosis. But, at least he did not charge me original diagnosis for $145... 


Anyways, the codes are still coming up after the guy cleared them. Let me know if you have any input on the situation or if you could link a similar forum where the user listed the solution that would be fine as well.


SIDE NOTE: I am also receiving the message system key faulty. My mechanic in Minnesota said that was simply due to the weight of the key in the ignition moving around. He said  it was no big deal and does not affect the car mechanically. The previous owner bought 2 new key fobs about 1 year ago. This happens with both keys. I have one with a lanyard and keychain on it that I use regularly and the other is just the fob itself. Can anyone confirm that this is true? I know it seems small but it is kind of annoying to hear it pop up often.


I'm sure the dealership will give me the info I need and I can update this post after the diagnosis Friday. If any of you smart Porsche pals can point me in the right direction before the  appointment I can at least prepare myself for what I'm getting into lol. 



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Yes, you will likely need a Porsche shop (not necessarily a dealer) with a PIWIS tester to further diagnose your system fault. The Porsche diagnostic system will run a series of tests that will narrow down the fault(s) and what needs to be fixed/replaced.


The comment about the key and the weight of items on a key chain is pretty much true for all cars. Best to keep the ignition key separate from other weighted items.

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The first fault (4WD System Faulty) triggers the fault in the PSM system. In other words, the problem resides in the former. The 4WD system electronics in these cars is essentially just the transfer case computer and the transfer case servo motor (+ rear lock diff if so equipped). Problems with these components are very common, especially in early year Cayennes. There are a number of threads on this topic, such as this one from a few days back:


Your fix is most likely replacing the transfer case servo motor and transfer case ECU. Any competent shop familiar with Porsches and owning the correct tools should have no problem diagnosing and repairing this issue. Both of these components can be replaced in under an hour without even needing the car on a lift.



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Great, thanks for the info! Definitely sounds like the issue I am having. 


So, from what I understand I can use the transfer case servo motor in the same year Touareg such as http://www.rockauto.com/en/moreinfo.php?pk=6326826&cc=1427228&jsn=378 or http://www.rockauto.com/en/moreinfo.php?pk=8019336&cc=1427228&jsn=379&jsn=379?


I would want to replace the ECU as well. And this would work? http://www.ebay.com/itm/2004-05-06-PORSCHE-CAYENNE-3-2-V6-TRANSFER-CASE-ECU-COMPUTER-CONTROL-UNIT-/232066304551?hash=item36083aca27:g:2WcAAOxyOalTbVPL&vxp=mtr


Sorry, to you this may seem simple. But, to me it is not. Hope you understand. I'm just a girl with a crying Porsche trying to get it fixed.. :helpsmilie:


Edited by hannah
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Sorry, I didn't mean to imply that this problem should be simple for any owner to solve. I was trying to say that if you get it to the right shop that they should be able to diagnose and fix the issue without much trouble.


Unfortunately, as you have probably already found, the servo motor and ECU are not particularly cheap parts. Even though it is extremely likely that these two parts are what you need to solve your problem, I recommend always getting a proper diagnosis to ensure you are not simply throwing parts at the problem. In my case the damage to the stepper motor was obvious once I removed it and opened it up.


As to your specific questions on the parts: I would avoid a remanufactured stepper motor. You also want to make sure that you are buying the revised version of this part. This is the one I bought two years ago when mine went: http://www.rmeuropean.com/Products/95562460101-MFG58.aspx. You are correct that the Touareg is the same. On the linked site the VW and Porsche part numbers x-ref to the same part and are priced the same.


The ECU that you linked to has a 2003 manufacturing date on it (09.10.03), so this is most certainly not the updated version of the ECU and it wouldn't be any better than the one currently in your car. It may be hard to find the updated unit on eBay. I tried but gave up and ordered one from the dealer (Porsche p/n 955-618-023-05). Part of the problem is that many cars have not been updated. Another problem was that I did not know what the corresponding VW part number was for the updated ECU (this is the 9-12 digit number that starts with 0AD) and this is the only part number listed on the ECU label. However, if you can find a 03-06 Cayenne transfer case ECU on eBay with an Oct. 2009 or later manufacturing date then it is probably correct. Again, the easy way out is to order the ECU from the dealer.





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Thanks for your input. Found a shop that I just took it to. You were correct it is the servo motor. However, they said I do not need to replace the ECU, that is still good. As far as what I thought was a minor issue with the system key faulty, turns out to be a bigger issue. He said my ignition switch is faulty and I have to get a new one. He said it has to be brand new due to the key programming. Can you confirm if this is true? He told me the ignition switch is almost a $600 part but I found new ones online for nearly half of that price.  He said when he orders it would come with everything including the sensors. Maybe that is why such a drastic difference? He is going to check into it for me more tomorrow and give me the part number and the exact price. I'll update once I find out...

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  • 6 years later...

I just solved my 4 wheel error code.  The problem started when the battery was nearing end of life.  After replacing the battery we still had the issue.  Next replaced the servo & then ECU to no avail.  Next we upgraded the battery from Interstate to OEM but that didn't work.  Porsche of Stevens Creek was of no help so I searched the web & found this at Pelican Parts and found a procedure to basically sync the system IT WORKED!  Sorry, I cannot find the link but I did summarize it in a text.

1. Activate off-road /Low Range mode/ driving program (use rocker switch) with gear shift lever in neutral position
2. Drive your car for a while (move forward/backward several meters)
3. Activate on-road /High Range mode/ driving program (use rocker switch) with gear shift lever in neutral position


It may "heal" your all-wheel drive system, e.g. resistor, which identifes mode in which system is and generates fault message when corroded - it happens when you do not use this feature for a long time...


I did this and drove around the block.  It's been a month and the error code has not returned.


We bought the vehicle in 2017 and never once adjusted the range.  I'd wager the first time it had ever been adjusted is when I followed the procedure.  

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