Thermostat intermittent working

What is your question?

Thermostat will work Correctly on some days. Noticed the problem the other day while driving. Thermostat started declining in temp, check engine light came on, heater started to blow cold air. I know the two are tied together. I'm assuming the thermostat is stuck open, was looking to see if anyone else has had a issue with this before I did into it.

What makes this problem better or worse?

Turn off air conditioning

How long has your 2004 Cadillac SRX had this problem?

2-3 weeks