mci-self-test-failure on a Tesla Powerwall+: Alert: MCI Self-Test Failure - string shows voltage during test then 0 V
Short answer
On a Tesla inverter, mci-self-test-failure means: Alert: MCI Self-Test Failure - string shows voltage during test then 0 V. The inverter stops until the fault clears or is reset. An engineer is needed to fix the cause.
Reviewed 24 September 2026 · 1 source
What it means
The manual says: Alert: MCI Self-Test Failure - string shows voltage during test then 0 V.
Likely causes:
- Faulty MCI (module-level rapid shutdown device).
- Faulty MPPT.
Is it safe?
Switch the inverter off at its isolator and call an engineer.
| Does the inverter stop? | Yes |
|---|---|
| Severity | Fault — needs a manual reset once the cause is fixed |
| Engineer needed? | Yes |
The inverter stops until the fault clears or is reset.
Resetting itself: no.
Manual reset: no.
What you can check
- Read the app; contact installer (DC-side fault - no homeowner action).
What the engineer will check
- DC Only mode string voltage checks; swap MPPT; MCI health tests.
Who to ask for: PV / DC fault finding.
Certification: Tesla Certified Installer (Powerwall is not user-serviceable); electrical work to BS 7671.
What you might notice
Sources
- Powerwall 2 / Powerwall+ Troubleshooting Manual - Setup and Install (Tesla One, en-us) ↗ · Reviewed 24 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 24 September 2026