When plugged to HBD II a message claims that the thermostat is BELOW coolent temp... The warning light ONLY comes on when I want to use the heater. I've looked at threads where people get this code but I havent found anyone dealing with the issue only when using the heater. Could it still be a faulty ECM?

 

Sorry new to this forum but it is a 2011 Impala Lt

 

Welcome to the forum, Chevy11! I understand you're seeking advice from the members, but I just wanted to chime in to let you know we're available via private message if needed. As customer care agents on the forum, we generally work in tandem with our certified Chevrolet dealerships in an effort to resolve vehicle concerns. With this being said, if you're thinking you'd like to visit one to address this, please don't hesitate to reach out. We only need your VIN, mileage, contact information, and preferred dealership to go this route.

Jasmine
Chevrolet Customer Care

 

is the coolant full? if its full then the most likely cause would be the thermostat or possibly the coolant temp sensor. ECM is a possibility but I wouldn't jump to that unless you know for sure everything else is fine.