Take it to a mechanic unless you are really familiar with cars. I am doing one right now, all dash assembley, including structural frame have to be removed to access this. Not a job for a novice.
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ooo. pull the dash. fun job.
It may need a heater core.
You need to remove instrument cluster. And the whole dash to access heater box. The heater box case has to be slpit in half to access heater core. A very timely and frustrating job. Take to a professional is what I recommend.
If you have not done this before, it is a very time consuming job. Replacing the heater core is not the problem. Getting to it is. Unless you are willing to start removing panels and know how to remove them without damaging the plastic panels and clips, I suggest you take it to a professional. It is just a matter of removing enough to actually get to the core. Once you get to the heater core, first drain the radiator enough to get the level below the heater hoses. Remove the heater hoses, and then remove and replace the core.
The heater core is located in the middle of the dash behind the center console. You have to take the console out to see the heater core.
I wouldn't think you could flush a heater core. you can flush a radiator. Heater core you would have to replace if it is leaking or stopped up
The hoses to the heater core can be disconnected under the hood. connect a water hose to the core, and try to flush the core to unclog it.
10000.00
you need to replace your heater core.
take it to the dealer
About 90 dollars if you do it yourself.