I just tried to do this on my 03 S and I got an alert saying it is already enabled... I intend to do this without the stalk so I can get just the temp reading. The only things I'm currently seeing are the odo reading and the trip counter. Seems like a similar issue was found here but I didn't have any luck with disconnecting the battery:
http://986forum.com/forums/boxster-general-discussions/63060-obc-enable-durametric.html
I am getting an error code 9114: PCM control unit and I suspect this is coming from the removal of the MOST connection to the stereo, amp, and cd changer. I ordered some MOST terminators from china for $2.50 each and will see if those fix both the 9114 code and the OBC.
Hybrid Mode
