The Mazda cx-5 comes with Automatic Emergency Braking. As I was driving on the highway at about 50mph, I tried to accelerate. As I accellerated, I noticed white smoke in my rear view mirror. Then the car starts slowing down. Suddenly the check engine light turns on and then error messages pop up on the dash. The one that I distinctly remember read "smart brake system malfunction.
I brought to the Mazda service and the tech told me that the air cleaner housing box got loose and that was what causing the car to slow down.
I told him about the smart brake error messages and he said that he didn’t find anything wrong with it.
The NHTSA has a Technical Service Bulletin regarding the smart brake error:
Can the air intake affect the smart brake sensor? or is there something more to this?
High temperatures can cause electronics to malfunction. Last week I was sitting in the sun reading my iPad. It shut down on its own and displayed a message saying it overheated.
The sensor? No. When the Powertrain control module detects a fault ancillary systems will be disabled. The automatic braking, stability control ABS, traction control etc. will be disabled. The radar sensor and windshield camera are not affected but the Smart Brake system will not operate.
That service bulletin is not for a check engine light, it is specifically for a Smart Brake system malfunction. If the camera malfunctions the system will not operate.
When the auto braking engages, the vehicle will not just slow, it will stop faster than you thought a vehicle could.
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I had the AEB kick in on my Mazda 6 when a car pulled out in front of me suddenly. I stabbed the brakes and the car stopped so quickly I was pressed against the seatbelt. I did not hit the car, but the rate of deceleration was phenomenal. You would know if the AEB had kicked in!!!
I was in exactly the same situation once on 2019 Accord where a car pulled in front and stopped.
AEB engaged pretty much simultaneously with me pressing on the brakes in unison.
The most surprised person in whole situation was the guy tailgating my car for the last block, but fortunately I was not hit on the back… and YES, I was surprised how fast car can stop 
What a coincidence! I had a Mazda6 on a business trip for the last 21 days. Nice car. I noticed the automatic braking as part of the adaptive cruise control. It seemed flawless to me. Very comfortable, too. There were a couple downers, though. That’s one loud car. Road noise was more than my 2017 Accord, and that’s loud. The information center was so last generation (or two). No video, and no song ID. GPS Girl was available for directions, but Apple Car Play visuals were only on my phone. If I was looking for a new car, this one isn’t it, at least in that trim level. They saved a lot of money on the display, as it isn’t interactive. There’s a buncha buttons on the center console to push, but it takes a while to get used to without looking at it. No way I would replace my 2017 Accord with a 2021 Mazda6. My Accord is just so advanced vs the Mazda6.
Most Mazda 6 rentals are “Sport” or “Touring” models. I drive a 2018 Mazda 6 GTR with the turbo engine and it is extremely quiet. The turbo does not rev nearly as high as the non-turbo engine (loads of low end torque) so it is much quieter than the lower trim lines. I plug my Android phone in for Android Auto and it works beautifully. My sister plugs in her Iphone and CarPlay works great, so I’m not sure what issues you were having. Both systems display perfectly on the center display of the car. That center display IS interactive, but not when you are moving. When moving you must use the scroll wheel on the center console because, you know, safety.
The GTR has a heads up display for the driver that is pretty sweet. And, in any event, the Mazda is all about the driving experience, not the massive tech. With the up-level GTR (turbo, larger wheels) you get great performance and driving fun along with pretty good gas mileage (I got 34 MPG driving to and from Baltimore this week and I was NOT driving slow).
I drove the Accord and the higher trim lines were comparable in performance but short on feedback from the road to the driver (compared to the Mazda 6). And for equivalent power and performance? It was about 3 grand more. You can buy a lot of stuff for 3 grand. And the seats in the 6 are much better than the Accord. Plus the Honda dealer was pretty snooty and the Mazda dealer was totally chill and relaxed.
It’s possible the white smoke you saw in the rear mirror was b/c the air/fuel mixture was overly rich. Not a brake problem in other words. A problem with the air cleaner box could cause an incorrect fuel mixture, as that part is often related to the function of the airflow sensor. The same problem could bog the engine & cause the car to slow down. If you notice the white smoke again, pull over and feel the wheels to see if any are hot. If they are the brake is probably engaging for some reason. Be careful b/c if the brake actually is engaging they might be very hot.
Note that an overly rich mixture may damage the expensive to replace cat, so if this occurs again take it back to the shop asap.
The reason I want none of that complex stuff on my car . More expensive stuff to go wrong and obviously from your experience potentially dangerous .
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The engine slowed because of a loose air cleaner lid.
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