EV Diagnostics
Verified EV diagnostic knowledge page

Tesla UMC_a004

Unable to charge with Mobile Connector Voltage too high / Try a different wall outlet

Common search variants: UMCa004 · UMC-a004 · UMC a004 · Search ignores case and common separators.

DriveNot yet established by verified evidence.
ChargeCharging with the affected wall outlet may be unavailable or interrupted. Tesla documentation directs the owner to try a different wall outlet.
ServiceNot yet established by verified evidence.
Confidence95%

Quick answer

UMC_a004 means the Tesla Mobile Connector detected wall-outlet voltage that is too high or an unexpected increase in supply voltage. Charging may be unavailable or interrupted. Tesla’s documented action is to try a different wall outlet.

This page separates verified manufacturer/regulator evidence from supporting material. Unsupported causes, repairs or safety conclusions are not guessed.

Video guides

Watch Videos

Relevant videos play here without leaving this diagnostic page.

No sufficiently relevant embeddable video has been accepted for this diagnostic yet.

Videos are supporting material and never override OEM or regulator evidence.

1. What does UMC_a004 mean?

UMC_a004 means the Tesla Mobile Connector detected wall-outlet voltage that is too high or an unexpected increase in supply voltage. Charging may be unavailable or interrupted. Tesla’s documented action is to try a different wall outlet.

2. Technical explanation

Tesla documentation submitted to NHTSA states that this alert occurs because the Mobile Connector detects either excessively high wall-outlet voltage or an unexpected rise in supply voltage from the outlet. This is an OEM alert, not a generic OBD diagnostic code.

3. What system is affected?

Tesla Mobile Connector and the AC wall-outlet supply used for charging.

4. How serious is this code?

Severity is not yet established by verified evidence.

5. Symptoms you may notice

  • The vehicle cannot charge.
  • Charging is interrupted.
  • The UMC_a004 alert is displayed: “Unable to charge with Mobile Connector Voltage too high / Try a different wall outlet.”

6. Possible causes

  • The Mobile Connector detects that wall-outlet voltage is too high.
  • The Mobile Connector detects an unexpected increase in supply voltage from the wall outlet.

7. Can I still drive the vehicle?

Not yet established by verified evidence.

8. Can I charge the vehicle?

Charging with the affected wall outlet may be unavailable or interrupted. Tesla documentation directs the owner to try a different wall outlet.

9. What you can safely do

  • Try charging with a different wall outlet.
  • For Mobile Connector status-light and charging-issue information, refer to the applicable product owner’s manual.

10. Step-by-step troubleshooting

  1. Use a different wall outlet and determine whether charging proceeds.
  2. Refer to the product owner’s manual for Mobile Connector status-light troubleshooting and charging issues.

11. When to contact service

Not yet established by verified evidence.

12. What the service center may check

  • Not yet established by verified evidence.

13. Possible repair or resolution

  • Tesla’s documented owner action is to try a different wall outlet. A further repair resolution is not yet established by verified evidence.

14. Affected vehicles

15. Related TSBs / service bulletins

  • NHTSA manufacturer communications reproduce Tesla owner-manual information for UMC_a004, including NHTSA Manufacturer Communication PDF 10250484 (published 2023-12-01): https://static.nhtsa.gov/odi/tsbs/2023/MC-10250484-9999.pdf
  • Additional NHTSA-hosted Tesla owner-manual communications in the supplied evidence also contain this alert information.

16. Recall information

  • Not yet established by verified evidence.

17. Official manufacturer information

Verified official-source evidence: Tesla owner-manual content hosted by NHTSA states that UMC_a004 can prevent or interrupt charging when the Mobile Connector detects excessively high outlet voltage or an unexpected supply-voltage increase. Example: https://static.nhtsa.gov/odi/tsbs/2023/MC-10250484-9999.pdf

19. Frequently asked questions

What does Tesla alert UMC_a004 mean?

It means the vehicle cannot charge, or charging is interrupted, because the Mobile Connector detects wall-outlet voltage that is too high or an unexpected increase in outlet supply voltage.

What should I do when UMC_a004 appears?

Tesla documentation says to try charging with a different wall outlet.

Can I still drive with UMC_a004?

Not yet established by verified evidence.

Does UMC_a004 identify a vehicle fault?

The verified evidence identifies the Mobile Connector’s detection of high or unexpectedly increased wall-outlet supply voltage. It does not establish a specific vehicle-component fault.

20. Sources & verification

Accepted ResearchVerified
Show all 58 verified sources
Tesla UMC_a004: Unable to charge with Mobile Connector Voltage too… | EV Diagnostics