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004

Sungrow 004 on a solar inverter: grid undervoltage detected

Verified with sources1 sourceReviewed Oct 4, 2026
Technician coming? See the 3 steps they must show you
Wall-mounted solar photovoltaic inverter
AsurnipalCC BY-SA 4.0Image source

Risk level

Medium

Proceed carefully and stop if the check is unclear.

Urgency

Medium

Quick answer

The Sungrow inverter measured grid voltage below its protection value (Grid Undervoltage) and stopped feeding in. It normally reconnects by itself when the grid recovers. If it repeats, note the days and times and tell your installer.

Safety first

Stop and check this first

  • Do not open the inverter or touch the AC cable: the manual requires AC and DC to be disconnected before any work, and it is a job for the installer.
  • Changing protection thresholds is not a home fix: they must follow the local standard and only the installer should adjust them, with the electricity company's approval where the rules require it.

Safe checks you can perform

  • Code on the display and in iSolarCloud
  • Time pattern and neighbours
  • Visible state of the AC breaker

Leave these tasks to a qualified professional

  • Do not attempt this professional task: Measuring the actual grid voltage
  • Do not attempt this professional task: Review of protection parameters
  • Do not attempt this professional task: Checking and tightening the AC cable

What a technician must be able to justify

Technician visit

These are the steps they must carry out and show you. Tick them as they work: if steps are skipped, do not accept a part swap.

These are not instructions for opening or handling the equipment yourself. They are the checks that should support a technical conclusion.

  1. Measuring the actual grid voltage

    What they doThe installer measures grid voltage at the connection point and compares it with the protection value set in the inverter.

    They must show youthe measured values and the configured protection value.

    In writingwhere and when it was measured, the values and whether the electricity company was informed.

  2. Review of protection parameters

    What they doChecks in the app or LCD that the grid standard and undervoltage thresholds match local regulations.

    They must show youthe parameter screen before and after any change.

    In writingthe grid standard selected and any value changed.

  3. Checking and tightening the AC cable

    What they doWith the system disconnected as the manual requires, checks that the AC cable is firmly connected.

    They must show youphotos of the AC connection before and after.

    In writingwhat was checked or tightened and the operating test afterwards.

Before accepting a part or repair

Nothing has been shown yet. Do not accept a part swap based on the code alone.

Follow these steps

Note: Follow the documented order. An error code identifies the affected system, but it does not prove by itself which part has failed.

  1. Code on the display and in iSolarCloud

    No special tools

    Who:
    you, with no tools and without opening the inverter.
    How:
    look at the LED indicator: steady red means a system fault according to Sungrow, and touching it shows the error codes on the display. In the iSolarCloud app go to Records and open Fault Alarm Record to see the detail and time of each alarm.
    Result that matters:
    confirming the code is 004 or 005 (Grid Undervoltage) and seeing how often and at what times it appears.
    If it appears once and the inverter feeds in again by itself:
    Sungrow says it normally reconnects once the grid returns to normal.
    If it repeats over several days:
    keep the history and move on to the next checks.
    Evidence to keep:
    screenshots of the Fault Alarm Record with date and time and a photo of the LED or display.

    Evidence: User Manual 1-Phase PV Grid-Connected Inverter SG2.0RS-S / SG2.5RS-S / SG3.0RS-S / SG3.0RS / SG3.6RS / SG4.0RS / SG5.0RS / SG6.0RS (SG2.0-6.0RS-UEN-Ver18-202211)

  2. Time pattern and neighbours

    No special tools

    Who:
    you, reviewing the app history.
    How:
    compare the alarm times with what happens at home and in the area: if they match peak demand, short outages or notices from the electricity company, write it down.
    Result that matters:
    knowing whether the fault follows the grid (fixed times, several neighbours affected) or appears unrelated to it.
    If it matches grid events:
    the cause is external and the installer can ask the electricity company for a measurement.
    If it appears with no clear pattern:
    tell the installer so settings and the AC connection get checked.
    Evidence to keep:
    a list of alarm dates and times and any known grid incidents.

    Evidence: User Manual 1-Phase PV Grid-Connected Inverter SG2.0RS-S / SG2.5RS-S / SG3.0RS-S / SG3.0RS / SG3.6RS / SG4.0RS / SG5.0RS / SG6.0RS (SG2.0-6.0RS-UEN-Ver18-202211)

  3. Visible state of the AC breaker

    No special tools

    Who:
    you, looking at the board without opening covers or touching wires.
    How:
    find the inverter AC breaker and check whether it is on. Do not dismantle anything or touch the inverter wiring.
    Result that matters:
    ruling out that the inverter is cut off from the grid by a tripped protection device.
    If it is on:
    the fault comes from the voltage, not the breaker; continue with the installer.
    If it is off or keeps tripping:
    do not reset it again and again; call the installer.
    Evidence to keep:
    a photo of the board showing the breaker position.

    Evidence: User Manual 1-Phase PV Grid-Connected Inverter SG2.0RS-S / SG2.5RS-S / SG3.0RS-S / SG3.0RS / SG3.6RS / SG4.0RS / SG5.0RS / SG6.0RS (SG2.0-6.0RS-UEN-Ver18-202211)

Still not solved

If the error persists, stop here. See what the technician must do and show you.

Where this code applies

A code is meaningful only inside the right product and version context.

Primary scope

System
Solar and energy
Brand
Sungrow
Product type
Solar inverter

Known code variants

  • Sungrow 004
  • Sungrow 004 subtensión de red
  • Sungrow 004 undervoltage
  • Sungrow 005
  • Sungrow código 4
  • Sungrow error 004
  • Sungrow fallo 4
  • Sungrow fault 4
  • Sungrow fault code 4
  • Sungrow grid undervoltage
  • Sungrow low grid voltage
  • Sungrow tensión de red baja

What it means

Sungrow groups codes 4 and 5 as Grid Undervoltage: grid voltage drops below the protection value set in the inverter, which disconnects to comply with the grid connection rules. The manual says it normally reconnects once the grid returns to normal. If it keeps happening, Sungrow asks for the actual grid voltage to be measured (and taken to the electricity company if it is below the setting), the protection parameters to be checked and the AC cable to be confirmed firmly in place. The code alone never proves that a part of the inverter is faulty.

Warnings and stop conditions

  • Mediumeditorial warning

    Do not open the inverter or touch the AC cable: the manual requires AC and DC to be disconnected before any work, and it is a job for the installer.

    Evidence: User Manual 1-Phase PV Grid-Connected Inverter SG2.0RS-S / SG2.5RS-S / SG3.0RS-S / SG3.0RS / SG3.6RS / SG4.0RS / SG5.0RS / SG6.0RS (SG2.0-6.0RS-UEN-Ver18-202211)

  • Loweditorial warning

    Changing protection thresholds is not a home fix: they must follow the local standard and only the installer should adjust them, with the electricity company's approval where the rules require it.

    Evidence: User Manual 1-Phase PV Grid-Connected Inverter SG2.0RS-S / SG2.5RS-S / SG3.0RS-S / SG3.0RS / SG3.6RS / SG4.0RS / SG5.0RS / SG6.0RS (SG2.0-6.0RS-UEN-Ver18-202211)

Symptoms and causes

Probable causes · in order

  • Grid voltage really is lowCommon

    The grid arrives below the set value, for example at times of high demand in the area. Sungrow asks for it to be measured and, if it is low, for the electricity company to be contacted.

    Evidence: User Manual 1-Phase PV Grid-Connected Inverter SG2.0RS-S / SG2.5RS-S / SG3.0RS-S / SG3.0RS / SG3.6RS / SG4.0RS / SG5.0RS / SG6.0RS (SG2.0-6.0RS-UEN-Ver18-202211)

  • Protection parameters set wronglyPossible

    The undervoltage protection value set in the app or LCD does not match the local standard. Sungrow asks for the parameters to be checked.

    Evidence: User Manual 1-Phase PV Grid-Connected Inverter SG2.0RS-S / SG2.5RS-S / SG3.0RS-S / SG3.0RS / SG3.6RS / SG4.0RS / SG5.0RS / SG6.0RS (SG2.0-6.0RS-UEN-Ver18-202211)

  • AC cable not firmly in placePossible

    A loose AC connection causes voltage drops at the inverter. Sungrow lists checking that the AC cable is firmly in place, which is installer work.

    Evidence: User Manual 1-Phase PV Grid-Connected Inverter SG2.0RS-S / SG2.5RS-S / SG3.0RS-S / SG3.0RS / SG3.6RS / SG4.0RS / SG5.0RS / SG6.0RS (SG2.0-6.0RS-UEN-Ver18-202211)

Virtual technician

Does 004 still appear after these checks?

Answer a few questions to narrow down the likely cause and the safest next action. Guidance only - it never replaces a professional.

Start diagnosis

Sources and technical references

  1. 1

    User Manual 1-Phase PV Grid-Connected Inverter SG2.0RS-S / SG2.5RS-S / SG3.0RS-S / SG3.0RS / SG3.6RS / SG4.0RS / SG5.0RS / SG6.0RS (SG2.0-6.0RS-UEN-Ver18-202211)

    Sungrow Power Supply Co., Ltd. · 2022 · manual

Sources: User Manual 1-Phase PV Grid-Connected Inverter SG2.0RS-S / SG2.5RS-S / SG3.0RS-S / SG3.0RS / SG3.6RS / SG4.0RS / SG5.0RS / SG6.0RS (SG2.0-6.0RS-UEN-Ver18-202211)reviewed 2026-10-04 · verified

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