Owners of other Mazda vehicles such as the CX-5, CX-3, CX-30, MX-30, CX-8, Mazda8 (MPV), MX-5 Miata, Mazda2 (Demio), Mazda3 (Axela), Mazda6 (Atenza) and Mazda5 (Premacy) may also find these DIY instructions to be helpful.

The compatible replacement "festoon" style light bulb is part number DE3175 which is available from various manufacturers such as Sylvania, Bosch, Philips and GE.

If you'd like to have brighter dome lights that will also last much longer before burning out like the traditional incandescent bulbs, install some DE3175 LED units.

The only tool needed to access and replace the light bulbs is either a small flat head screwdriver such as from a precision screwdriver set or a plastic pry bar tool.

To prevent from scratching the plastic surfaces, you can either cover the tip of your screwdriver with a thin micro fiber cloth or instead use a small plastic pry bar tool.

Carefully insert the blade of the screwdriver in between the lens cover and the light housing near the front edge (closer to the front of the vehicle).

Very gently pry out the lens cover to release the "C" shaped retaining clip from the plastic mounting bar or "peg".

Do NOT pry near the rear edge of the lens cover (closer to the back of the SUV). There are two plastic tabs on the rear edge of the lens cover that can easily be broken.

Repeat the process to pry out the retaining clip on the other side of the lens cover near the front edge (closer to the windshield and the front of the SUV).

Once the two retaining clips on the front edge have been released, pull the lens cover out of the light housing.

Set the lens cover aside in a safe place.

If the old light bulb was recently turned on, be careful when you remove it. The old bulb might still be hot enough to burn your fingers.

The OEM (original equipment manufacturer) light bulb part number was KHA12V8W 27D10A.

If you'd like to have brighter dome lights, install some compatible replacement DE3175 LED bulbs.

Line up the lens cover with the opening in the light housing.

First, re-insert the two plastic tabs on the rear edge into the housing.

Gently push on the lens cover to pop the two "C" shaped retaining clips over their corresponding plastic mounting bars or "pegs".

You should feel or hear the retaining clips "click" securely into place.

Make sure the lens cover is securely installed and that it is flush with the light housing at every edge.

To test the new light bulbs, press the front edge of the lens covers to activate the "On / Off" switches.

Tip - If you installed an LED bulb and it doesn't work, try removing it from the socket, rotating it 180 degrees and pushing it back into the socket. Some LED bulbs are "polarized" and will only work when the "+" positive and "-" negative electrical contacts are in the correct orientation.

Don't forget to write down the bulb change in your car's service records.

For more, please check out all of the 2016-2021 Mazda CX-9 DIY Repair & Maintenance Guides.