Two weeks ago my CEL came on and the code was P1121. I checked the coolant level and everything seemed fine, so I figured I'd take it in soon. This week, my heater isn't working - it blows fine, but it is ice cold air. I again checked the coolant level and topped off the overflow, and nothing. Is the P1121 error related to the heating issue? Thoughts on this???
Check the coolant level in the radiator itself, not just the overflow reservoir. You need to remove the large black plastic panel over the radiator to access the radiator cap. DTC P1121 means that the engine coolant flow valve is stuck. That valve routes engine coolant between the cabin heater core and the coolant heat recovery canister. If the valve is stuck in the wrong position that would explain why the cabin heater is not working.
When my coolant valve stuck, it was due to a low coolant level. The coolant acts as a lubricant for the valve. After a top-off of the coolant (it was low due to air bubbles left in when the coolant was drained/refilled), the valve loosened up. That was 155k miles ago and no further problems with the valve. I hope that you have the same experience, JeffD
