How to turn off self-calibration for the MH-Z19B co2 sensor?

My CO2 graph isn’t looking healty, before I got some nice periodical spikes which triggered an air exchange, but overtime the Co2 sensor seems to have mostly flatlined.

I suspect the automatic self-calibration of this sensor is to blame. but Im not sure how to check if its enabled or how to disable it incase it is.

Anyone able to help me out here?


I suspect this checkbox should suggest that the self-calibration is turned off, which leaves me puzzled as to why my Co2 readings have flat lined.

edit2: I’m going to try a manual zero-point calibration after exposing the sensor to the outside atmosphere for 20 minutes and see if that changes anything.

Per the datasheet (, there’s no way to check the status of ABC. The datasheet recommends calibration every 6 months.

The datasheet also mentions that automatic self calibration isn’t suited for greenhouse setups which is how I have it. (mostly because we don’t really have a steady baseline of 400 ppm I reckon) from what I understand the automatic calibration happens every 24H and the 6 months calibration would be when the automatic calibration is turned off.

Are you saying we have no way to tell if the self calibration is on or off? (self calibration = ABC?)

Correct. ABC = Automatic Baseline Correction. The datasheet/sensor provides no way to query any ABC setting stored on the sensor. You can only send the command to enable or disable it.

Without ABC enabled, you’ll have to be a bit more attentive to drift and conduct manual calibration, when appropriate.

Do you happen to have on hand how to send the command to disable?

The Input sends whichever command you have configured every time the Input is activated. You can find the function with the command in the Input module, as well as the datasheet I linked in my first reply.

Alright, I think I understand now,

with the checkbox for the ABC turned off it should send the command to disable the automatic calibration every time the sensor is activated. So In theory the ABC isn’t turned on on my setup, and my problem isn’t caused by it.

Correct. It sends the Disable ABC command every time the input is activated, which occurs when you press activate or when Mycodo boots up and automatically starts the input.

looks like either the manual zero calibration or the switching out mushroom substrate that wasnt producing did the trick