AirGradient Forum

O-1PST – 4-4-4 / 5-5-5 blue LED pattern after clean flash + all basics ruled out

#1

O-1PST DIY kit (new)

  • All wiring confirmed correct (PM1 = PM sensor, PM2 = CO2 sensor, both fully seated)
  • Using the exact same power adapter + cable that works perfectly on my indoor AirGradient
  • WiFi signal strong at the location (same spot where indoor unit works fine)
  • Indoor unit on same 2.4 GHz network works perfectly
  • After multiple full erase + flash + re-setup: blue LED does exactly 4 blinks ×3, then 5 blinks ×3, then completely off
  • Faint internal CO2 LED is blinking (board + CO2 sensor alive)
  • App shows “seen once” with new timestamp each power cycle
  • Pattern repeats identically every time

All common causes (power, wiring, signal, network) ruled out. Any ideas??

#2

Hi @Mbetters, welcome to our community.

Would you mind collecting some logs from the monitor using this tool?: Online Debug | AirGradient Knowledge Base

I’ll help you find out what might cause the issue.

Anyway, in case it’s helpful, this is what each LED indicator means on the Open Air running on firmware 3.6.x or newer.

https://www.airgradient.com/documentation/kb/airgradient-open-air-indicator

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#3

Hi there. Circling back to issues with this new outdoor sensor. The log reveals a hardware issue it appears. What do you advise? (fyi, the forum rules will not allow me to upload the txt file directly or to paste links so below is a selection of the log)

11:03:24]Detected OPEN_AIR_OUTDOOR
[11:03:24]Firmware Version: 3.6.2
[11:03:24]Found S8 on Serial1
[11:03:25]Init SGP41 success
[11:03:25]initializing PM sensor
[11:03:25]cleared 0 byte(s)
[11:03:25]setting active mode
[11:03:25]7 byte(s) written
[11:03:25]Detected PM 1 on Serial0
[11:03:25]Firmware Mode: O-1PST
[11:03:25]Set S8 AbcDays successful
[11:03:25]S8 type ID: 0x10E
[11:03:25]S8 serial number: 0x7654A0F
[11:03:25]S8 memory map version: 0x31
[11:03:25][AGSERIAL] Info: IICSerial initialized
[11:03:25][AGSERIAL] Warning: IICSerial failed open serial line, retry…
[11:03:26][AGSERIAL] Warning: IICSerial failed open serial line, retry…
[11:03:26][AGSERIAL] Warning: IICSerial failed open serial line, retry…
[11:03:27][AGSERIAL] Error: IICSerial failed open serial line, give up…
[11:03:27]Cellular module not available, using wifi
[11:03:27]Attempt connect to configured ssid: 1070229308
[11:03:27][LocalServer] Info: Init: airgradient_d83bda1b7528.local
[11:03:27]MQTT is not configured, skipping initialization of MQTT client

#4

Here is an AI summary highlighting issues it sees…

1. Repeated IICSerial Communication Failures (Hardware/Interconnect Issue — Most Critical Recurring Error)

[AGSERIAL] Info: IICSerial initialized
[AGSERIAL] Warning: IICSerial failed open serial line, retry…
[AGSERIAL] Warning: IICSerial failed open serial line, retry…
[AGSERIAL] Warning: IICSerial failed open serial line, retry…
[AGSERIAL] Error: IICSerial failed open serial line, give up…

2. Cloud Communication Failures (HTTP 400 Bad Request — Blocks Full Functionality)

[AgWifiClient] Error: Failed post measures to server with response code 400
[AgWifiClient] Error: Failed fetch configuration from server with return code 400

3. Frequent Unexpected Resets / Boot Loops (Stability Problem)

ESP-ROM:esp32c3-api1-20210207
Build:Feb 7 2021
rst:0x15 (USB_UART_CHIP_RESET),boot:0xe (SPI_FAST_FLASH_BOOT)
…
Reset reason: ESP_RST_UNKNOWN

4. Other Supporting Indicators of Instability

  • WiFi connection attempts after every reset, even though RSSI is decent (WiFi RSSI -57 / -58 / -59).
  • Repeated full sensor re-initialization on every boot (S8, SGP41, PM sensor) — wastes time and indicates no persistent stable runtime.
  • Configuration shows “country”:“TH” (Thailand) on what is presumably a US/Texas device — minor mismatch but could contribute to config 400 errors.
  • Firmware 3.6.2 is reported as up-to-date, but the OTA check and repeated boots suggest underlying instability in this version for O-1PST.
#5

Updated the firmware again and started over. Readings are there. Here is the current error…

[05:10:15][AgWifiClient] Error: Failed post measures to server with response code 400
[05:10:15]
[05:10:15]Online mode and isPostToAirGradient = true
[05:10:15]
[05:10:15]Free heap: 154036
[05:10:16][AgWifiClient] Info: Fetch configuration from REDACTING THE LINK SO TYHIS WILL POST TO YOU
[05:10:18][AgWifiClient] Error: Failed fetch configuration from server with return code 400

#6

Hi @Mbetters, sorry for my late reply.

[AgWifiClient] Error: Failed post measures to server with response code 400
[AgWifiClient] Error: Failed fetch configuration from server with return code 400

These 2 lines are our primary focus here, which reflects the LED status that you mentioned earlier. It means the O-1PST couldn’t get configuration from the server, nor could it post the data to the server.

I have checked your Dashboard and found that the input serial number of the O-1PST didn’t match the log above (the old serial number was the serial number of the PM2.5 module (PMS5003T), not the O-1PST itself). I’ve edited it to match your log already. Could you please take a look at your dashboard to see if the O-1PST is online now?