'04 Honda Civic Hybrid
 

My Hybrid has 200,000 miles and the IMA light just went on.
It has been very hot and I thought I may be able to help it along. When it weather cools, the light goes off.

I know my Ford EH has a battery back cooling filter, does the HCH have one too? Maybe better airflow may help?

Does anyone know how to change and with what part number?

Re: '04 Honda Civic Hybrid
 

As far as I know there is no filter involved, but I think it has a battery cooling fan...you can see the vent for it up above your rear seats in the center. That's why they say to never place items up on top of that vent; it needs the ability to circulate air to help cool the battery.

You can try checking some of the online Honda parts websites, like Bernardi Honda parts or Majestic Honda parts. Sometimes you can find a good picture of the parts involved in the various systems of the car.
(I just took a look at both websites; it's called the IMA PDU COOLING UNIT.)

It has been really hot this summer. Usually I park in the garage, but lately I've been stuck parking outside. I place one of those reflective sunvisor things in the back window when parked for a long time (usually people use them on the front window while they park to keep it cool for their own benefit, but I figure using it in the back window might help deflect the hot sun off the battery. It's just a bit of a pain remembering to take the thing off whenever I hop in the car for a drive).