Comma.ai on a 2017 Mazda 3

The Best Car I've Ever Owned

The 2017 Mazda 3 GT is probably the best car I've ever owned. That's not a throwaway line — I've owned a lot of cars, most of them bad ideas, and this one is genuinely excellent. We got here by way of a 2014 Mazda 3, which was the first car I ever took on a track. That car was later in an accident, and the story of how well it held up ended up in a publication. Through that, we got preferential pricing on a new one. Nearly 100,000 miles later, the 2017 is still the daily driver and still the benchmark everything else gets measured against.

However, the thing I least like (liked) about it was the factory lane-keep assist. It was, fine...in the way that a screen door is fine as a front door: technically it's there, it does something, but it's not really what you want. It requires hands on the wheel at all times, cuts out below 18 mph, and gives up way too easily. I wanted something better. The problem: the Mazda 3 is not on Comma.ai's official supported vehicle list.

So I did what any reasonable person does when they want to make a $10,000 car drive like a $50,000 car: I Googled it. Turns out there's an entire community — on Reddit and on a dedicated Discord server — of people who had already solved this exact problem. I trusted random people on the internet, followed their instructions, and it worked.

How It Works

The core issue with the Mazda 3 is that its column-mounted power steering motor doesn't have the torque or firmware to handle autonomous lane centering. The fix is a $300 motor from a 2022 or 2023 Mazda CX-5, which does. Swap out two bolts, unplug one connector, don't lose the small black gear inside, reinstall. That's the hardware side.

The Comma device itself mounts behind the rearview mirror in the existing powered mirror sensor housing. A single wire runs from there — tucked into the headliner, down the A-pillar, along the door weatherstripping — to the OBD2 port under the dash. That's the entire physical installation. Then you connect to Wi-Fi, load FrogPilot (a community fork of OpenPilot with a specific Mazda 3 profile), and it works.

There's also an optional upgrade: swap the stock windshield camera for one from a CX-5 with stop-and-go support, and you get full adaptive cruise down to 0 mph instead of cutting out at 18 mph. I haven't done this yet because my commute doesn't require it, but I have read that this is technically possible for those who want it.

How Well Does It Actually Work?

According to the device, approximately 92% of my driving is done autonomously. I love this. The car steers, maintains speed, and centers itself in the lane completely hands-free. The driver-facing camera monitors attention, so you still have to be present, but your hands don't have to be on the wheel. For a car that was never supposed to do any of this, it's remarkable. This is also an excellent time to remind anyone reading this to ALWAYS pay attention while driving, regardless of your ADAS setup.

The limitations are real: it doesn't read stop signs or traffic lights, and without the CX-5 camera it still cuts out at lower speeds. When approaching a stopped car it sometimes waits a beat too long and brakes harder than you'd like. But for highway and arterial driving, it's genuinely excellent.