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#19097·esphome

pmsx003 (pms5003) Start character 1 mismatch: 0x00 != 0x42

Author: bednimCreated Sep 11, 2026Updated Sep 18, 2026

The problem

hello,

since some time i started to receive Start character 1 mismatch: 0x00 != 0x42 and no values for pms5003...

sorry - I can't recall around which esphome update this stopped working :(

Which version of ESPHome has the issue?

2026.8.2

What type of installation are you using?

Home Assistant Add-on

What platform are you using?

ESP32

Component causing the issue

pmsx003

YAML Config

yaml
esphome:
  name: esphome-web-27d048
  friendly_name: ESPHome Web 27d048
  name_add_mac_suffix: false

esp32:
  variant: esp32
  framework:
    type: arduino
    advanced:
      minimum_chip_revision: "3.1"

# Enable logging
logger:


# Enable Home Assistant API
api:

# Allow Over-The-Air updates
ota:
  - platform: esphome

wifi:
  ssid: !secret wifi_ssid
  password: !secret wifi_password

uart:
  id: pms_uart
  tx_pin: GPIO1   # ESP32 TX0 (Hardware TX pin)
  rx_pin: GPIO3   # ESP32 RX0 (Hardware RX pin)
  baud_rate: 9600

sensor:
  - platform: pmsx003
    type: PMSX003
    uart_id: pms_uart
    pm_1_0:
      name: "Particulate Matter <1.0µm Concentration"
    pm_2_5:
      name: "Particulate Matter <2.5µm Concentration"
    pm_10_0:
      name: "Particulate Matter <10.0µm Concentration"

Anything in the logs that might be useful for us?

txt
21:51:06.842][W][pmsx003:138]: Start character 1 mismatch: 0x00 != 0x42
[21:51:06.850][W][pmsx003:138]: Start character 1 mismatch: 0x00 != 0x42
[21:51:06.857][W][pmsx003:138]: Start character 1 mismatch: 0x02 != 0x42
[21:51:06.862][W][pmsx003:138]: Start character 1 mismatch: 0x00 != 0x42
[21:51:06.874][W][pmsx003:138]: Start character 1 mismatch: 0x03 != 0x42
[21:51:06.874][W][pmsx003:138]: Start character 1 mismatch: 0x00 != 0x42
[21:51:06.884][D][uart_debug:113]: <<< 42:4D:00:00:00:D4:00:B2:00:CB:02:53:00:BF:01:F6:00:16:00:07:00:91:00:00:00:00:00:02:00:03:00:03
[21:51:06.907][W][pmsx003:138]: Start character 1 mismatch: 0x03 != 0x42
[21:51:06.908][W][pmsx003:138]: Start character 1 mismatch: 0x00 != 0x42
[21:51:06.908][W][pmsx003:138]: Start character 1 mismatch: 0x00 != 0x42
[21:51:06.910][W][pmsx003:138]: Start character 1 mismatch: 0x00 != 0x42
[21:51:06.917][W][pmsx003:138]: Start character 1 mismatch: 0x00 != 0x42
[21:51:06.928][W][pmsx003:138]: Start character 1 mismatch: 0x00 != 0x42
[21:51:06.931][W][pmsx003:138]: Start character 1 mismatch: 0x00 != 0x42
[21:51:06.939][W][pmsx003:138]: Start character 1 mismatch: 0x00 != 0x42
[21:51:06.942][W][pmsx003:138]: Start character 1 mismatch: 0x00 != 0x42
[21:51:06.945][W][pmsx003:138]: Start character 1 mismatch: 0x00 != 0x42
[21:51:06.950][W][pmsx003:138]: Start character 1 mismatch: 0x00 != 0x42
[21:51:06.964][W][pmsx003:138]: Start character 1 mismatch: 0x00 != 0x42
[21:51:06.974][W][pmsx003:138]: Start character 1 mismatch: 0x00 != 0x42
[21:51:06.974][W][pmsx003:138]: Start character 1 mismatch: 0x00 != 0x42
[21:51:06.974][W][pmsx003:138]: Start character 1 mismatch: 0x00 != 0x42
[21:51:06.985][W][pmsx003:138]: Start character 1 mismatch: 0x00 != 0x42
[21:51:06.988][W][pmsx003:138]: Start character 1 mismatch: 0x00 != 0x42
[21:51:06.995][W][pmsx003:138]: Start character 1 mismatch: 0x00 != 0x42
[21:51:06.997][W][pmsx003:138]: Start character 1 mismatch: 0x00 != 0x42
[21:51:07.006][W][pmsx003:138]: Start character 1 mismatch: 0x05 != 0x42
[21:51:07.013][W][pmsx003:138]: Start character 1 mismatch: 0xA1 != 0x42
[21:51:07.116][D][uart_debug:113]: <<< 00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:00:05:A1
[21:51:07.578][W][pmsx003:151]: Payload length 0 doesn't match. Are you using the correct PMSX003 type?
[21:51:07.584][W][pmsx003:138]: Start character 1 mismatch: 0x00 != 0x42

Additional information

uart debug apparently confirms valid data being received - but I can't verify that..

thanks!

Source: esphome/esphome

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