2006 Prius - Heater Flow Control Valve Question

I have a 2006, 155k miles, bought new Feb 2006. Have not had a lot of trouble or maintenance beyond oil changes and tires, one front wheel bearing, couple of 12v batteries. For purposes of this discussion, the engine coolant has not been changed since new. For the last 3 or 4 years, I have the check engine light on all winter and then it goes off in the summer. I don't bother to go find out what it's complaining about.

My heater issue:

I believe there would be a hot water line valve that is opened and closed when the cabin heater core needs more hot water or less hot water. Since I don't have a control lever that is cable connected to said valve, it must be electronically opened and closed by an actuator of some kind, driven by a computer request. This is my theory.

I'm in Chicagoland so I pretty much 'get it' when it comes to having a warm car to drive in the winter. The thing has an engine the size of a Harley, it just doesn't burn enough gas to make enough heat. Summer is coming, live with it.

My problem in the cold days with the heater on blower on full or 80%, is that every so often (and more often as we get older) it will blow cold. As if the fluid control valve is not opening. Then I can switch from floor heat to mid-vent heat to defrost and after 1 or two switches that control valve will manage to open properly and I get heat again. I even think I can hear a bit of a mousy wimper of it opening that valve when I do this, maybe I'm just wanting to hear it in my head.

I searched around here and couldn't find a thread that seemed to address this issue directly, so if there is one can you point me to it?

Am I on target with how this system is built and how it works, or can someone line it out for me?

Is there a how-to write up on how to change it, or a video. If not, and if I can tackle this on my own I will make one.

What parts do I need and where are they hiding on the car, can I get to them in the garage on a DIY day?

Your advice is much appreciated!

Thanks, -Daron

 

I wonder if the hinge on the air flap is getting crumby, or the servo is needing replaced.

I should check if the coolant level is low for any reason. It just seems like I can give it a little wack with a hammer (change from one heat selection to another) to remedy the issue, so I was thinking the computer is telling it to do something and then some physical part is no longer making the movement to deliver.

 

You are correct on all of this, all of those fluids need changed out.

I did see some P1121 threads, but after reading them I thought they dealt with coolant to the canister and not really about the cabin heat, so thanks for clearing that up.

I just called my Toyota dealer to get an idea what kind of money it takes to get some of this stuff done. It was a bit of an odd experience. The lady who answered the service option line had no idea about doing service work, she was just typing what I said into some text box and setting up my appointment. I asked her what it would cost, how long it would take, and she had no idea and seemed a bit offended that I would ask. I helped her with how I expect things to be done and she is going to email my list to a service manager who can figure it out and call me.

It's always fun to get the cost from the dealer so I know how many hundred I am saving by busting my own knuckles under the car.

Thanks for the input, -Daron