How does the "smell" sensor actually work?

[jac]

That darn sensor (64116917001) has such a limited life span, I must have replaced it 5 times by now. :-)

So, I am contemplating replacing it yet again... And started to wonder about how it actually works. Does anyone know?

For example, what allows it to detect a bad smell? And what is its electrical signal/output when there is no bad smell vs when there is a bad smell?

[X5chemist]

From FCP : "Product Information
This clever little sensor detects the levels of oxidizable gasses flowing through the radiator. When a specific threshold is reached, the HVAC recirculation flap closes for a specific time after the noxious gasses are no longer present."

Apparently, it's an air temp sensor. If it's too hot, it closes the air flap.

[Henn28]

How do you know it has failed? Did it throw a code?

[Bdc101]

Originally Posted by X5chemist

From FCP : "Product Information
This clever little sensor detects the levels of oxidizable gasses flowing through the radiator. When a specific threshold is reached, the HVAC recirculation flap closes for a specific time after the noxious gasses are no longer present."

Apparently, it's an air temp sensor. If it's too hot, it closes the air flap.

Didn't the FCP description say it detects oxidizable gases, not temperature?

[X5chemist]

FCP calls it an air temperature sensor.

[andrewwynn]

FCP is wrong. It measures hydrocarbons in the air and the HVAC system will use that as input to decide to close off outside air for a few minutes at a time to block certain pollutants. I've monitored the sensor values when passing road construction and for example new asphalt will most certainly engage the automatic system to set recirculating air.

I guess the thing has a heater in it to work it's magic and the heater fails so it will stop working.

[X5chemist]

What are the units of measurement?

[andrewwynn]

It generates a voltage proportional to certain pollutants in the air. I think the range goes from near zero to near 5v. And somewhere near the middle it will close the outside air flaps. I doubt there is any ppm quantity calibration to the voltage scale but I'd be curious to find out.

I have watched in real time both the output of the auc and the flap position. The system definitely works but you get no feedback just less smell.

[jac]

@Henn28: Yes, it throws a code.

@AndrewWynn: So if the sensor is broken, then the flap should be permanently closed or open when in "auto" mode. Hopefully it's designed to signal "close" when it fails! :-)

Do you know where the flap is located? Can we actually get a look at it without taking stuff apart or even hear it close/open? I am thinking of running a test by sending various voltages manually and see if it activates the mechanism.

[jac]

@Henn28: Yes, it throws a code.

@AndrewWynn: So if the sensor is broken, then the flap should be permanently closed or open when in "auto" mode. Hopefully it's designed to signal "close" when it fails! :-)

Do you know where the flap is located? Can we actually get a look at it without taking stuff apart or even hear it close/open? I am thinking of running a test by sending various voltages manually and see if it activates the mechanism.