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PCM slipping into transit mode

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I had a fellow RennTech-er visit yesterday to diagnose a problem on his 2004 Cayenne S with PCM2.0 (Version 3.0 software).

The unit gave a system error message to the effect "no navigation, no amplifier, no cd changer, no telephone" and then shut down to a blank screen and would not turn on. I plugged in the PIWIS and entered the PCM Module. Only the Gateway was shown as present, and no faults in it.

In the absence of any other ideas, I ran the vehicle handover routine. Bingo! It woke up the PCM, and everything started working perfectly. Today, the error message came up again, and it has slipped back into sleep mode.

Has anyone else had this happen? The fellow is visiting again on Tuesday to try again, but I'm at a bit of a loss as to what to look for. Any ideas appreciated.

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Richard, as far as i can remember we had at once such a problem on a 996 Turbo, the advice that we received were including some acts as battery condition, loading/alternator, power drop by starter motor actvation, checking the PCM power network, etc... with no results, at the end we have the PCM replaced, problem solved. I hope you can find the problem and am curious to hear the solution.

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Thanks for the reply. I have had occasions when the alarm module on 986's and 996's have slipped into transit mode, but once woken up they have stayed awake. I have never heard of this on the PCM before though. The owner does have another (used) PCM unit available, so I think we will try that, to see if it has the same trouble. Of course, the other unit may have different faults......

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Well things have gone from bad to worse. I tried the handover routine on PIWIS and it failed. It just froze on the 'Please wait" screen after starting the handover and didn't go any further. This is weird, because it was successful last time. I thought it might be a problem with PIWIS, but it did exactly the same with my PST2. We also tried the replacement PCM unit, but exactly the same thing happened.

I think it must be some kind of intermittent communication problem on the CAN or MOST bus, or on the diagnosis line. If I/he get to the bottom of the problem I'll post again.

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I had a similar(???) problem on my new 2013 CD. It would be in Battery Protection mode / transit. I could clear it manually with the "backup" button on the steering wheel. When I took it to the Porsche dealer and asked them to check it out as the battery was new, they discovered a switch or circuit (sorry, I'm not 100% sure which is was) under the drivers seat that had been set such that tranit mode and battery protection was always on. After they corrected it, they did a vehicle handover to be sure all was ok. That seemed to fix my situation.

In your friend's case, could he have a bad or weak battery and/or some issue with the wiring under the drivers seat?

Edited by stronbl
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