We noticed my wife’s Model X was taking longer than usual to charge. The following notification on the small screen was only visible while the car was charging:
So the warning message was “Charge rate reduced – Wall plug temperature high. Wall outlet and wiring inspection recommended” and the charging rate dropped from the normal 32 amps to 16 amps.
It was a bit of a fluke that we noticed this as we almost always charge at night. We did notice that it was taking longer than usual to charge, but we didn’t think too much about it as it was still charged when we got up in the morning.
I decided to look at my Model 3, as I use the same charger. I thought maybe it was her car having issues. I learned that you can find notifications by going into the “Service” menu option, and on the bottom left was an option for “Notifications” (see image):
My front tire pressures are looking a bit high there. It was probably after I had been driving in the heat that I was looking this up, as my tires are usually at 45 when cold. Also, they are usually much more similar, so not sure what was up with that. When I checked my Model 3 Notifications, I was surprised to see I had issues charging as well:
It turns out each night after one hour of charging, a notification alert appeared with the time and the label UMC_a017 with the warning “Charge rate reduce – Wall plug temperature high. Wall outlet and wiring inspection recommended. So apparently this was not an issue with my wife’s Model X, as both cars were getting the same warning.
When I clicked to see the details of the alert, this was the text:
Charge rate reduced – Wall plug temperature high
Wall outlet and wiring inspection recommended
High temperature detected by Mobile Connector alerts indicate the outlet used to charge is becoming too warm, so charging has been slowed to protect the outlet.
This is not typically an issue with your vehicle or your Mobile Connector, but rather an issue with the outlet. A warm outlet may be caused by a plug that is not fully inserted, a loose building wiring connection to the outlet, or an outlet that is beginning to wear out.
To regain normal charge speed, make sure your adapter is fully plugged into the outlet. If charging speed does not return to normal, contact an electrician to inspect the outlet and building wiring connections to the outlet and complete any repairs needed.
If the outlet is worn, it should be replaced with a high-quality outlet. Consider upgrading to a Tesla Wall Connector for greater convenience and highest charging speed.
I then swapped the Mobile Connector main unit with the one that came with my car, using the same wall plug into my Connector. I haven’t had any warnings since.
So it seems the error message is due to the Mobile Connector that we’d been using for the last two years, and not the wall outlet or wiring in the house.
We had her car in for service for a different issue (yellow display border) and asked them to check out the Mobile Charger. They told us the problem was with the firmware which will get updated if we keep using it. I haven’t tried it since, but I plan to before it is out of warranty.
The exact wording they put in the service summary was:
Concern: customer states issue charging
Verified proper operation of charging cable. False “bad charge cable” faults due to current firmware bug
Correction: General Diagnosis
So there you have it. Let me know if you’ve had similar problems in the comments. I’m curious if anyone else has had the problem and had it resolve with continued use and a firmware update. I wish they could have just updated the firmware at the service center, but maybe it’ll update the next time I try to use it.
Some other people in October 2020 did say there was a firmware issue that seemed to get fixed also around that time. Weird that there would be a new firmware issue two years later.
In August 2021, someone posted their similar issue and they seemed to fix it by removing the plug part from the Mobile Connector and then re-inserting int, and then plugging it back in. Then someone else mentioned the same error message I have UMC_a017 and had an electrician check everything and was told it was fine. Also was told by Tesla that the mobile connector was fine. I didn’t see any follow-up from that particular user, so I don’t know what solution they found.
At some point I’ll switch back the Mobile Connector and see how long the issue persists before an update gets pushed. Of course, it could be that the plug head just needed to be removed and reseated as it worked for at least one other person. If it works right after the switch, then I’ll assume that was the issue.