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Random PSM failures and problems. Please help

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What can i do. They are trustful people. I believe. I dont think they change parts which are not neccessary to change. What is surprising me really is the fact that piwis show codes at MAF . They change the part but car continue to show same behaviour. I thought piwis is piwis. Checking the system means checking the complete system. From your last message i understand, checking transmission and PSM is a different process?!

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I just wondered as the three things they fixed only the MAF could have any affect on PSM.

The fact that it goes into limp mode would make want to run a transmission diagnostic. Plus if your complaint is the PSM they should also be running that diagnostic.

I would like to learn what is behind this failure. I thought if a part is damaged its not working. But this car is sometimes driving and sometimes not. Sometimes thousand km without PSM complaint and sometimes nonstop. What is this?

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  • 2 weeks later...
  • Moderators

Have they already checked the brake light switch, on the pedal or the unit, depending MY? The control box can also be broken, loose contact or so, anyway all this has to be measured out in one or an other way.

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  • 3 weeks later...


I took the car from porsche service. Piwis show failure in throttle body again but this part is already new.

I understand piwis is not the right tool to get rid of this frustrating problem.

Problem. Piwia is just showing errors in parts which are new or almost new.

They checked almost every ground point at the car because somebody told me this could be a problem.

They checked alternator. Brake light switch is new.

I could drive more than 1000 km without any problem last weeks.

Today again. PSM workshop and engine running a little bit rough.

Left it on parking lot for all day. At evening car starts and runs without.

Problem and no PSM warning on the display.

I called porsche. They are frustrated as much as i am.

I am affraid to drive . Impossible situation.

I am ready to give the car away.

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  • 2 months later...

I just started having this problem with my 2004 cayenne turbo. During heavy acceleration last night truck almost stalled and psm workshop maintenance warning light came on. When clearing codes I found cam positioning sensor and misfire on cylinder 7. After clearing codes car stalled and wouldn't hold idle, I had to two foot it home keeping it reved. I noticed car was in limp mode and would not boost at all. First I'm changing the plugs and coils as truck has 111,000 on it then I'm going to look at fuel pump. Also I notice vibration under acceleration, could be coils? Driveshaft? Should I do a trans fluid and filter change too? Would fuel pump throw psm light, would coils do it? Am I having one problem or 3?

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  • 8 months later...

Sorry i arrived late to this discussion. I am also having PSM failure issues as well. Mine is caused by a yaw sensor failure and it caused a complete brake failure. Could not stop the car without hitting a pole. All happened very quickly. Anyone else with this issue.

The car is a 2005 cayenne s bought new and has 93 k miles now.

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I had the same problems. All what i can tell you: my porsche shop changed a lot of parts. All where shown as faulty by the porsche diagnostic system. Nothing changed. The PSM light came randomly back. For my experience it has more to do with a weak battery or some other electric cremlins. Did you install any aftermarket parts connected to the system? Did you check if you have maybe water on the passenger side footwell which is effecting the Cables there?

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  • 4 years later...

Hi, I have an -03 Cayenne S with the same type of issues. Problem started and I suspected the battery which I then replaced. After that it keeps on giving fault codes, to which I delete with my Icarsoft Por II device. It usually works for a while and then for no reason the PSM light comes on again. 


Did anyone manage to fix this? It seems as if I'm not the only one with this issue.


I've read somewhere about ABS sensors going bad, but I have no idea whether or not that will work.

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  • 5 months later...

This kind of problems causing fault codes for many many parts. That’s why I spent thousands on parts and work.  In the end o believe the problem is a electric one. Somewhere ! Wet carpet? Water in footwell?  Any electrical aftermarket stuff in your car? 

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