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I have a 2013 Mazda 3 i Touring sedan, with about 39,500 miles on it. I've had no issues with it before. And I had a mechanic look it over about 6 months ago when I bought it.

This just started last night. While driving on the highway, my car thought that my key was not in the car. It then dropped to a lower gear while I was trying to accelerate. After a while the check engine light came on. I got off the freeway, looked up common issues, one is that the check engine light can come on if the gas cap is loose. So I tightened the cap, turned the car back on, and the light was off.

I continued driving, and then I had the same issue. This time I unscrewed the gas cap and put it back on. Tried this a few times, and the light was still on. Then this morning, when I was going to go to an auto parts store to get a code readout, the engine light was off. So I decided there wasn't much I could do about it. So I went grocery shopping, which required driving on the freeway. It was fine. But then when I drove home, the light came back on, and again I had issues with acceleration. I took it straight to an auto parts store, but when I turned the car on for them to read the code, the light was off again. Went home, and the light did not come back on.

The only thing different between when this issue started and before is that the temperature outside went down by 30 degrees (at the high) compared to Friday. Plus there's been really bad wind here, in the 25 mph range, with gusts up to 50 mph. But I can't think of anything else that's changed. I did get my wiper fluid filled a few days ago, but that seems very unlikely to cause an issue like this, unless Jiffy Lube did something weird when filling the fluid. I have also been meaning to replace my air filter. Though the filter isn't quite at the end of its life yet. Gas tank is a little more than half full. And the problem started when I had 3/4 of a tank. I also haven't heard any weird noises, as far as I can tell.

Any ideas what could be the issue?

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    Welcome to the site! Glad you could be here and asking questions. You still need to take it somewhere and get the codes read. While the CEL may not be illuminated, the code will still be stored in the computer until it is cleared (as long as there is one there). Get it read and let us know. – Pᴀᴜʟsᴛᴇʀ2 Nov 20 '16 at 16:58
  • Thanks for the response! Is there anywhere in particular to bring it? The technician at the store tried reading it with a code reader and there was no code. – NeuralLotus Nov 20 '16 at 20:49
  • Next time the light comes on don't shut the car off before getting the code read. You could also ask a shop to scan the code for you it should be stored in history depending on the code. – Ben Nov 20 '16 at 22:09
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When is the last time you got a tune up? Some modern cars like yours can have problems like this when you've got a misfire, or it could be even more simple, like an oxygen sensor. My car had a check engine light for a bad O2 sensor and wouldn't do very good at higher speeds, and also would downshift hard if any type of load were put on it (ex. going up a small hill) definitely just find out what that code is and hopefully it is just a O2 sensor or something.

  • Furthering your O2 theory - a downshift when the engine is low on power is likely – Brydon Gibson Dec 13 '18 at 13:24
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If it is not finding/seeing the key, I would check the connection of the antenna that the key system uses and also replace the battery in the key. If those two relatively cheap fixes don't help then get a qualified shop to dig into it.

Drastic changes in temp can affect connections.
If the key battery has not been replaced it could be low.

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