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Found some wiring diagrams relating to the 12V outlets (AKA Cigar Lighter!) CigarLighterPages.pdf
Haha JFP--as I was writing my response, I couldn't help but think "wow, somebody actually likes that start/stop feature!"
Have you eliminated these possibilities from the manual? I know all sorts of things got funky on mine when it had a weak battery. Page: 153 The Auto Start Stop function is available with limited functionality in the following situations, for example: – If the air conditioning or passenger compartment heating is operated at a high setting or if the defrost function is run for long time periods. – If the battery charging condition is low. – On upward or downward slopes. – During internal vehicle test procedures, e.g. automatic engine checks.
Almost definitely a clogged AC evaporator drain--I've had this occur on my 2011 Turbo as well. Loosen the spring clamp holding the rubber drain boot onto the evaporator and be ready for some water as you disconnect the boot from the evaporator. Once the evaporator drains, blow compressed air into the boot and through the firewall--this should free your clog. While you're down there, you might want to change out your cabin air filter--actually, anytime I replace my cabin air filter, I now blow compressed air through the drain as a preventative measure.
Found this while out searching for something completely different. Not sure when Porsche Gen3 TPM started, but this exactly describes the system on my 2011 and 2013. The 3rd generation TPM system operates on the principle of unidirectional communication between the wheel electronics and control unit. This means that the wheel electronics can communicate with the control unit, but the control unit cannot communicate with the wheel electronics. The wheel electronics units send the currently measured tyre pressure, the direction of rotation, the temperature of the air in the tyre and the remaining service life (of the battery) as well as a specific ID from the wheel that is currently turning at specified intervals. The wheel position is learned automatically from the side and axle specifications. The direction of rotation of a wheel is detected by acceleration sensors in the wheel electronics (left/right detection). Axle sensing (front axle/rear axle detection) is performed based on differentiated sound levels between the front and rear axle, where the central antenna is fitted close to one axle (high level). The levels received from the other axle are correspondingly low. The wheel electronics units communicate with the control unit in various modes. Depending on the current mode of a wheel electronics unit, it sends telegrams to the control unit at defined intervals. Normal mode: Normal mode is active while the vehicle is driving (after Burst mode has ended). Sleep mode: Sleep mode is activated as soon as the vehicle remains stationary for longer than 5 minutes. The wheel electronics then send no more telegrams. If the ignition is switched on while the wheel electronics units are in Sleep mode, no tyre pressures are displayed (display in instrument cluster: "-.-"). Tyre pressures are only displayed again when the vehicle is driving (see Burst mode). Burst mode: If the wheel electronics units are in Sleep mode and the vehicle is accelerated to over 25 km/h (15 mph) from stationary, the wheel electronics units switch to Burst mode. The wheel electronics units send their telegrams for 60 seconds at fast intervals. If a new set of wheels is used or wheel electronics units were replaced, the TPM system must be taught. When teaching the TPM system, the control unit stores the wheel IDs of the wheel electronics units and assigns a position to them. New wheel electronics units can be taught by selecting a new set of wheels in the instrument cluster. The system is then in learning mode and re-assigns the wheel IDs that are received. But the system also detects a wheel change if the stored information does not correspond to the information received. The control unit then displays a message on the instrument cluster prompting you to select the newly fitted set of wheels. The wheel electronics units can be taught while the vehicle is driving and while it is stationary. Teaching while driving is recommended. The wheel IDs can also be taught without using the System Tester. The following points must always be observed: Allow an idle time of at least 5 minutes before teaching the wheel IDs (wheel electronics units are then in Sleep mode). Briefly accelerate the vehicle to over 25 km/h (15 mph) in order to teach the wheel IDs (wheel electronics units are then in Burst mode). Then continue driving at any speed (even < 25 km/h or 15 mph) for max. 10 minutes. Teaching was successful if a pressure reading is displayed in the instrument cluster for all wheel positions.
Is it possible it's just the PSM in combination with driving style (and differing thresholds based on sport/normal)? The brakes on my 2011 CTT are noticeably different depending on how I drive--there was that ONE time I drove nice and easy in normal mode on the way to church, haha! from the manual pg 190: Examples of PSM control operations – Brake system prefilling: The brake system is prepared for possible subsequent emergency braking if the accelerator pedal is released suddenly and quickly. The brake system is prefilled and the brake pads are already applied gently to the brake disks.
That I can't be sure of; however, my wife's 2013 Diesel works the same way--I'm guessing it's Porsche standard.
No programing required. I just cycled through the appropriate entries in the Tire Pressure section of the Multi-Purpose Display, then after a couple minutes of driving, ops normal.
About 1 year ago, for my 2011 Turbo, from PartsGeek.com: 2011 Porsche Cayenne TPMS Sensor - UVS2000 HUF Intellisens - $40.74 Working great so far!
Your owner's manual will have the OEM wheel specs, then I have found the following site helpful: https://www.wheel-size.com/calc/?wheel1=275-45-20X9ET57&wheel2=275-45-20X9ET60&fcl=50mm&scl=50mm&wcl=30mm&sr=0mm
Nice to hear you were able to get that fixed! Since this might be in my future, I am curious as well--were you able to do this yourself? Especially concerned that Don got foiled--haha! What did that part cost? Related to your problem Don (although probably a long shot considering you just had that area opened up), I also had odd fluctuations with my AC. I didn't pull any codes, but discovered the problem when my passenger's Louboutin's got soaked on a high G turn! Cleared the clogged AC evaporator drain and everything returned to normal.
I don't have any experience with those parts, but if you do try them, please report your findings--I've got a switch starting to go bad too! Thanks.
Not sure how much theft deterrent value the switch has--I was able to drive around as normal even when the system was engaged--so, I am actually not quite sure what gets shut down in order to protect the battery. My guess is that it shuts off all those noises the car makes when it's just sitting there. Anybody know what this switch really does?
Problem SOLVED. The switch is located underneath the driver's seat, just to the left of the battery box. The switch is easily accessed through the outboard most pre-cut section of carpet joined with a plastic cover (see photo). If you remove the seat and peel back the pre-cut carpet covering the battery you will have a much better view. BTW, the seat is very easy to remove. This switch has got some funky design features. The last 3 pictures should illustrate the features and the solution to my problem. Notice the channel that guides the sliding switch is in the shape of a C. I believe the FORWARD position allows the switch to be locked into what I would call Discharge Protection Manual Engagement--use this position when storing or transporting your vehicle to help prevent battery discharge. The AFT and OUT position is where the switch is located after an automatic triggering of the Discharge Protection logic (think circuit breaker tripped position). With the switch in any position between here and FWD, the Discharge Protection remains active. The AFT and IN position is visually not very distinct from the AFT and OUT position. I found it basically by accident and it is more easily determined to be in the correct position by feel rather than visually. The switch on my vehicle does not naturally "like" to go into that position, it takes a little finagling. Verify it's in the correct position by turning the ignition ON and observing the lack of Discharge Protection caution message/yellow battery indication on the MFD. I suppose this switch tripped because my old battery was weak and/or during the replacement due to low voltage from my jump start pack. Confounding the problem is the switch design--in the darkness of an underseat switch you might think that it just moves forward and aft. You might also not perceive the approximately 1mm difference in position from normal to tripped. Also a switch label and/or a mention in the manual wouldn't hurt!
My iCarScan behaves as you described, it lets you think you can write the data, then reports unable with some ECU related error. So, I also thought it might be the battery and put a smart charger to it while it was connected to the vehicle. My caution actually changed to: "Battery discharge protection active Capacity 100%". Based on the caution, I think my car seems to think the capacity of my battery is at 90-100%--why the discharge protection remains active...unknown, Unless an answer shows up here, I'll probably do as you suggest and disconnect-charge-reconnect and see what happens. Perhaps the simple act of depowering the entire vehicle will reset the system as well--although I don't relish the thought of restoring all my settings. So what do you make of the switch next to the battery? If nothing else, would you mind peeking at yours and let me know what position it is in? BTW, I always see about 14.5-14.7V on the MFD (never drive in anything other than sport!)