sporadic Four Wheel Drive System Faulty - not the usual suspects

[pugface]

Hi guys. I have a 2006 Cayenne Turbo S, 218K miles, had it for 9 years

 

I occasionally get the 4-wheel drive system faulty error, usually within 60 seconds of starting the car. It seems to be getting more frequent this year, and my usual 'remedies' aren't working - I even tried a new TC ECU

 

Usual advice is to check battery of transfer case stepper motor, which I've done. I'm checking my records

2017 new battery

2019 Used Transfer case motor

2020 New transfer case motor

2022 new battery

2024 Cleaned contacts on transfer case motor

2024 new battery

2024 Another new  transfer case motor

2024 Replaced transfer case ECU with used unit

 

Where else to look? There are lots of stories about wiring harnesses under the carpet - could that be a suspect? I do live in south Texas, it is pretty hot and dry down here...

 

Another wild guess I've been thinking about - my car has always cranked hard at startup. I've had people stop in in the parking lot and tell my my battery is dying, but it has been this way all 9 years I've owned it without trouble, so I figured its a Cayenne thing. Could a weak starter be dragging voltage down enough to trigger errors in the transfer case module?

 

I just drove the car to town, and go the error on the way in (hadn't driven Cayenne in a week or so). Got it leaving my appointment. Stopped for a donut, on leaving there, the error went away and I drove home fine.

 

I got the Antigravity batter tester attached, it reports cranking voltage of 10.78V when I got the error and 11.02V when it was good (if that even matters)

 

I checked the transfer case codes with my Foxwell scanner when I got home. It says code 2039 - Transfer box potentiometer

 

Anyone have thoughts? 

Thanks

pf