About a year after getting my S, I started to have issues with charge current reductions significantly more often than the occasional instance. This was often accompanied by a "charging problem" message on the dash. I also had the charge port go thru a lock/unlock/lock cycle 2 or 3 times after plugging in. I brought it to Tesla's attention, and they looked at logs, but found no smoking gun. They suspected my early HPWC may be having issues, and because the design had been revised, had newer fuses, etc... they gave me a replacement. (awesome service, btw). As a test before swapping the new HPWC in, I cleaned my charge port and cable connector contacts with some electrical cleaner and a small industrial-style swab. (with breaker off). Boom! Problem went away. Fast forward to a couple of weeks ago... just about another year later. Once more charge current reduction issues several nights a week. The lock/unlock dance when inserting the cable. Last night the car failed to charge completely, and VisibleTesla reported "Disconnected" when the scheduled charge should have started. Inserting the cable today, and the car did the lock/unlock shuffle 3 or 4 times, and the port went red and the dash read "Check charge cable". A couple of quick blasts of electrical cleaner, a couple of insertion/removal cycles to scrub the contacts a bit, and: Bingo! Connected without issue and happily charging for a few hours now. I've just added charge port/cable cleaning to my annual maintenance when I also change my cabin air filter.