It’s the early warning of one, caught by a sensor designed for exactly that. The Mobile Connector stopped charging precisely because the plug-outlet connection was building heat, and overheated receptacles are a well-known origin of garage electrical fires. One alert after a half-seated plug is a non-event once re-seated. A repeating alert, a hot faceplate, or any discoloration means stop using the outlet and get the electrician in: this is the cheap moment to fix it.

Is my Tesla or my Mobile Connector broken?

Almost certainly not. Tesla states outright that this alert points at the outlet and its wiring rather than the car or connector. The Mobile Connector is the smoke detector here, not the fire. The same connector on a healthy outlet should charge indefinitely without complaint, which is also a usable test: if UMC_a008 follows the connector to a known-good outlet at another location, then have the connector looked at.

Can I keep charging on this outlet until the electrician comes?

If the alert appeared once and vanished after you fully seated the plug, cautious continued use with an occasional temperature check is reasonable. If the alert has repeated, treat the outlet as off-duty: charge elsewhere (another circuit, a public charger, a Supercharger), until it’s inspected. If you have no alternative, dropping the charge amperage from the car’s charging screen reduces the heat, but it’s a bridge to the repair, not a substitute for it.

What will the fix cost?

Usually little. An electrician visit to tighten wiring terminals or swap in a quality receptacle typically runs in the low hundreds, parts included: a commercial-grade 14-50 outlet itself is cheap. If the diagnosis grows into circuit work, that’s more, but you’d want to know either way. A hardwired Wall Connector with installation is the bigger ticket (commonly several hundred to over a thousand with labor), bought for convenience and robustness rather than necessity.

UMC_A008 Tesla: Unable to Charge: Wall Plug Temperature High (Outlet and Wiring Inspection Recommended)

Moderate

Quick answer

UMC_a008 means the temperature sensor in your Mobile Connector’s wall plug got hot enough that charging was stopped to protect the outlet. The car and the connector are fine; the heat is coming from the outlet side: a plug not fully seated, a loose wiring connection, or a worn-out receptacle. Take it seriously; hot outlets are how electrical fires start.

What it means

Tesla’s Mobile Connector has a temperature sensor in its wall plug for exactly one reason: an outlet that’s overheating is dangerous long before anything visibly burns. UMC_a008 means that sensor saw the plug-to-outlet connection getting too warm, and the connector shut the session down to protect the outlet. Tesla is explicit that this does not indicate a problem with your car or your Mobile Connector: the heat is being generated where the plug meets the building’s wiring.

The physics is worth one sentence: electrical resistance at a poor connection turns charging current into heat, and EV charging runs near an outlet’s full rating for hours at a stretch, a duty cycle household receptacles rarely see otherwise. Tesla names the three usual sources: a plug not fully inserted, a loose building-wiring connection behind the outlet, and an outlet that’s simply wearing out and no longer grips the plug’s blades tightly.

The honest division of labor: re-seating the plug is yours; everything behind the faceplate belongs to an electrician. Tesla’s guidance is to have the outlet and its wiring connections inspected and repaired, to replace a worn receptacle with a high-quality one (for 240V outlets, a commercial/industrial-grade receptacle is the meaningful upgrade), and: their suggestion, but a sound one for daily charging, to consider a hardwired Wall Connector, which eliminates the plug-and-outlet interface entirely.

UMC_A008 symptoms: what you'll notice

Charging stops and the touchscreen or app shows “Unable to charge: Wall plug temperature high”
The Mobile Connector’s wall plug or the outlet faceplate feels noticeably warm or hot to the touch after charging
In advanced cases: discoloration, a warm plastic smell, or visible browning around the outlet, stop using that outlet entirely

Common causes

Ordered from most to least likely.

1.

Plug not fully inserted into the outlet

The only cause you can fix yourself. A partially seated plug touches the outlet contacts over a smaller area, and a smaller contact area at the same current means concentrated heat. Tesla’s first instruction is simply to seat the adapter fully.
2.

Loose building-wiring connection at the outlet

Behind the faceplate, the building’s wires attach to the receptacle’s terminals, often with screws that loosen over years of thermal cycling. A loose terminal is a resistance heater hidden in the wall, and tightening it is a quick job for an electrician.
3.

A worn or low-quality outlet

Receptacle contacts lose spring tension with age and use; a plug that slides in too easily isn’t gripping. Daily EV charging finishes off an aging outlet quickly. The fix is a high-quality replacement, for 240V charging outlets, commercial/industrial grade.
4.

An outlet circuit never meant for continuous EV load

Older garages and shared or daisy-chained circuits can run warm at sustained near-rated current even with sound connections. An electrician evaluating the circuit, not just the receptacle, settles whether the installation matches the load.

How to fix it: diagnosis, step by step

Cheapest and most likely checks first.

1 Let it cool, then check the one thing that’s yours

Unplug, give the plug and outlet time to cool, and feel both: note which side held the heat. Then plug back in, fully and firmly, so the adapter is completely seated. If charging resumes at normal speed and the alert stays gone, an incompletely seated plug was likely the whole story. Keep an occasional hand on the outlet for the next few sessions anyway.
2 If the alert returns, retire that outlet and call an electrician

A recurrence means real resistance heating at the outlet or its wiring: exactly what Tesla’s alert exists to catch before it escalates. Stop charging there, and have an electrician inspect the receptacle and the wiring connections behind it, tightening or repairing as needed. This is a small, inexpensive visit; deferring it is how melted outlets happen.
3 Replace a worn outlet with a quality one

If the outlet is worn (loose grip on the plug, discoloration, age), have it replaced rather than coaxed along. For a 240V charging outlet (NEMA 14-50 and similar), specify a commercial/industrial-grade receptacle; the cheap ones aren’t built for daily hours-long load, and the price difference is trivial against the risk.
4 For daily charging, consider eliminating the outlet entirely

Tesla’s own closing suggestion is the structural fix: a hardwired Wall Connector has no plug-and-receptacle interface to overheat, charges faster, and is the right tool if the car charges at home every night. If you stay with the Mobile Connector, charging at a reduced amperage (set from the car’s charging screen) also lowers the heat at a marginal outlet while you arrange repairs.

Parts & tools you may need

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Related codes

CP_A066Charging Equipment Not Ready: See Equipment Instructions to Start Charging

Frequently asked questions

What does code UMC_A008 mean?: UMC_a008 means the temperature sensor in your Mobile Connector’s wall plug got hot enough that charging was stopped to protect the outlet. It’s moderately serious: you can usually keep driving gently, but diagnose it soon.
Is this a fire risk?: It’s the early warning of one, caught by a sensor designed for exactly that. The Mobile Connector stopped charging precisely because the plug-outlet connection was building heat, and overheated receptacles are a well-known origin of garage electrical fires. One alert after a half-seated plug is a non-event once re-seated. A repeating alert, a hot faceplate, or any discoloration means stop using the outlet and get the electrician in: this is the cheap moment to fix it.
Is my Tesla or my Mobile Connector broken?: Almost certainly not. Tesla states outright that this alert points at the outlet and its wiring rather than the car or connector. The Mobile Connector is the smoke detector here, not the fire. The same connector on a healthy outlet should charge indefinitely without complaint, which is also a usable test: if UMC_a008 follows the connector to a known-good outlet at another location, then have the connector looked at.
Can I keep charging on this outlet until the electrician comes?: If the alert appeared once and vanished after you fully seated the plug, cautious continued use with an occasional temperature check is reasonable. If the alert has repeated, treat the outlet as off-duty: charge elsewhere (another circuit, a public charger, a Supercharger), until it’s inspected. If you have no alternative, dropping the charge amperage from the car’s charging screen reduces the heat, but it’s a bridge to the repair, not a substitute for it.
What will the fix cost?: Usually little. An electrician visit to tighten wiring terminals or swap in a quality receptacle typically runs in the low hundreds, parts included: a commercial-grade 14-50 outlet itself is cheap. If the diagnosis grows into circuit work, that’s more, but you’d want to know either way. A hardwired Wall Connector with installation is the bigger ticket (commonly several hundred to over a thousand with labor), bought for convenience and robustness rather than necessity.