404 on a SMA Solar Technology AG Sunny Boy: The inverter has disconnected from the utility grid. A stand-alone grid or a very large change in the grid frequency was detected
Short answer
On a SMA Solar Technology AG inverter, 404 means: The inverter has disconnected from the utility grid. A stand-alone grid or a very large change in the grid frequency was detected. 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: The inverter has disconnected from the utility grid. A stand-alone grid or a very large change in the grid frequency was detected.
Part involved: grid frequency / anti-islanding / DC injection monitoring.
When it shows: The inverter has disconnected from the utility grid. A stand-alone grid or a very large change in the grid frequency was detected.
Likely causes:
- SMA corrective measures: Make sure there is no power outage or work being done on the utility grid and contact a grid operator if necessary. Check the grid connection for significant short-term frequency fluctuations.
Is it safe?
| Does the inverter stop? | Yes |
|---|---|
| Severity | Fault — clears by itself when the condition goes |
| Engineer needed? | Yes |
The inverter stops until the fault clears or is reset.
Resetting itself: yes.
Manual reset: Automatic when condition clears.
What you can check
- Read the event number and message in the SMA Energy app / Sunny Portal (ennexOS) or the inverter's web interface and note the date/time for your installer. A red LED on the inverter means an event has occurred.
- Check whether there is a power cut or grid work in your area.
- If it happens once and the inverter resumes feeding in on its own, no action is needed; if the event keeps recurring, contact your installer.
What the engineer will check
- Check grid frequency stability and AC wiring to the feed-in meter; for 601 check for DC on the grid connection; any change of monitoring thresholds only with DNO approval and SMA Service.
Who to ask for: PV installer / electrician; DNO liaison.
Certification: Installer liaison with the DNO; any change to grid-protection settings needs DNO agreement (G98/G99) and the manufacturer's installer/grid code.
What you might notice
Sources
- Operating manual SUNNY BOY 3.0/3.6/4.0/5.0/6.0 ↗ · SBxx-1AV-41-BE-en-21 Version 2.1 · page 87 · Reviewed 24 September 2026
A code explains what the controller detected, not a confirmed root cause.
Reviewed: 24 September 2026