Why did the heater stop working in 2011 terrain

are there any bulbs burned out?

good luck I believe there are two to four It depends on your engine.

There may be water in the gas tank. If there is, then a complete fuel system flush is in order and replace the fuel filter. Make sure the engine is warmed up some before you try to start it. Oil doesn't move well inside the engine at that temperature. A block heater and a battery heater , if you don't already have them , should be used.

You paid for it, take it back. Don't let them get away from not fixing your truck.

It isn't enough for the thermostat to work but also to verify both the heater (water) flow and return is getting virtually as hot as the top radiator hose as systems can airlock and sometimes other things can happen.

The heater matrix is unlikely to be blocked or coated considering the age so if plenty of heat is potentially available the reason it isn't emerging in the car is likely to be a matter of control - jammed flaps, disconnected linkages, faulty electric or vacuum servos, electric or vacuum supply interrupted or defective control circuitry.

There could be several reasons for this.
The internal heat is generated from the engine coolant system and is controlled via an control mechanism which you activate by adjusting the internal heat settings.
This control could be faulty, the air circulation fan inside your cab could be faulty or it could be a simple blown fuse.
In many cases where a leaking heater system could cause engine overheating a lazy mechanic would bypass the heater function and restrict the engine coolant from circulating through the heater coils.

My suggestion is to check all the above and you should have the problem sorted, good luck.

You have a plugged heater core.

The heat shouldn't have anything to do with your car turning off and on. If there is a knocking while the heat is on then you probably have a heater motor going out in you.

The BCM - body control module turns on this lamps , the BCM has fuse's that supply battery voltage to it . The brake pedal position sensor is a input to the BCM ,as is the turn signal switch . The odds of this being a fuse are astronomical . Having a qualified repair shop that has a professional type scan tool ,one that can read code's in the BCM ,would be the first place to start . Could save hours of diagnostic time . Rather then looking at all the fuses in all fuse boxes . But if you like too , look here http://www.bbbind.com/free-tsb/ Free wiring diagrams . Enter vehicle info. year , make , model an engine . Under system click on lighting , then under subsystem click on stop lamps . Click the search button then the # 3 blue link - stop lamp circuit .

I have had these same issues with my 2011 Terrain. I just read on the equinoxforum.net that there is a softwear update/upgrade (# PIO285) available. It is supposed to fix these problems. It is recommended that you take your vehicle to a GM dealer with this information. I am taking mine next week. Good Luck!