top of page


CO2 Sensor

Description of Fault

A CATALYST CO2 Sensor Fault indicates the return air CO2 readings are out-of-limit. A CATALYST CO2 Sensor Fault Alarm is generated when the CO2 sensor readings are high (2000 ppm) or low (0 ppm).

A CATALYST CO2 Sensor Fault Alarm will automatically reset when the CO2 registers a reading with an approximate value between 400-1200 ppm.

Possible Causes

A CATALYST CO2 Sensor Fault is typically caused by:

  • Shorted or open CO2 sensor cable (during installation).

  • Damaged CO2 sensor cable caused by the return damper or loose wire nuts.

  • Failed CO2 sensor.

  • Improper voltage to the sensor.

  • Shorted input on the controller.


From eIQ Platform

  1. On the eIQ Platform, navigate to the Status page of the unit.

  2. Verify the CO2 reading under the Return Air temperature.

    1. If the CO2 reading is 0 ppm or 2000 ppm a qualified technician to visit the site for further troubleshooting.

    2. If CO2 reading is between 400-1000 ppm contact TW for support.

On Site

  1. Access the CO2 sensor located in the return air duct.

    1. Inspect the CO2 sensor wire nut connections to the YELLOW W/ PURPLE STRIPE 4-C CABLE.

    2. Inspect the CO2 sensor and wire for damage.

    3. Inspect the wiring of the sensor for the presence of 24V AC between the BLACK and RED wires of the yellow w/ purple stripe 4-C cable.

    4. Measure DC voltage coming from CO2 sensor on the Brown wire connected to the green wire on the CATALYST Yellow with a Purple stripe.

      1. Does the DC voltage measurement match the readings on the eIQ Platform? 10 volts would be 2000 ppm, 5 volts 1000 ppm.

      2. If not remove the connection brown wire from the green conductor coming from the yellow with a purple strip wire from the CATALYST. Verify that the DC voltage measurement doesn’t change.

  2. Contact Transformative Wave for further assistance at or (855) 867-2333.

bottom of page