"...Poor grid quality.." (and charge rate hs been reduced). This touch-screen message misled me for months. It kept me from locally submitting a service order. Had I not purchased a Tesla Wall Connector, but instead, stayed with the NEMA 14-50 connection, I would still be wallowing in grid issues.
After reporting the touch-screen message to my local power company, I was exceedingly fortunate to receive same-day consultation. They agreed there might be a voltage drop problem. In less than 5 more days, a 7-man crew arrived with a new pole transformer and larger gauge power drop to my home. But, this did not cure the problem: Touch screen message still insisted that I had "poor grid quality"!
BTW, another possible warning symptom: hot charging cable. I dutifully replaced my cable and the 14-50 outlet, to no avail! At this point, I ordered a Tesla Wall Connector. The Las Vegas Wall Connector team was very patient and helpful in getting the on-line features working. But then, max current was onlt 32 A on a 60 A breaker and new #6 AWG wiring. Touch screen keep saying "...poor grid quality..." All electrical work was provided by a professional contractor.
After again dialing the 800 Wall Connector help number, the Buffalo Wall Connector team took over and, after working with me several hours , correctly diagnosed the problem: and, in writing, urged me to make an immediate service appointment. I did so, and after several weeks, the new charger arrived. I now have the full 48 amp available. Meanwhile. 50,000 miles was creeping up fast.
Along the way, I have learned some interesting things. A service note received a couple of weeks ago indicates that not all Model 3's, specifically the RWD version, offer a 48 A charger. Some are only 32 A. If you are using a NEMA 14-50 cable, you will never know this, because max amps for a 14-50 are 32! Similar to others writing here, my charger incrementally failed: 48 A (I guess) >32 A > 16 A > Zero A. Total failure occurred as I waited for a replacement. (Others have correctly stated that the AC charger is three each 16 A units , with the available amperage dependent on wall connector/wire and breaker sizes.) My Model 3 is a 2018 LR RWD.
Once more, kudos to CPS Energy, our locally owned power company, to the Wall Connector team in Buffalo, whose letter to me made possible a no questions asked battery charger replacement, and to the Tesla San Antonio Service Department, whose patience and competence in dealing with this complex problem were exemplary! Once more, if your Touchscreen says "...poor grid quality" AC charger failure may be the likely defect!