* A clogged rear heater core: The core itself might be blocked, preventing coolant flow to the rear heater.
* A faulty rear heater core valve: This valve controls the flow of coolant to the rear heater. If it's stuck closed, no coolant will reach the core.
* Low coolant levels: While this would affect both front and rear, a significant leak *could* preferentially affect the rear system if the leak is closer to the rear.
* A blockage in the rear coolant lines: Similar to a clogged heater core, debris or corrosion could restrict coolant flow.
* A failed rear blend door actuator: This is less likely to cause *only* cold air in the rear, as it typically affects both temperature and airflow direction, but it's a possibility.
Before replacing anything, it's crucial to:
1. Check coolant levels: Ensure your coolant reservoir is full and that there are no obvious leaks.
2. Check the rear heater hoses: Feel the hoses leading to and from the rear heater. If one is significantly colder than the other when the heater is on, it suggests a blockage or problem with the core or valve.
Only after checking these things should you consider replacing parts. Replacing the heater core is a more involved process than simply replacing a valve, and requires potentially removing some interior trim.
