On CX5s and other Mazda's with the i-stop system, i-stop may not activate after the battery has been replaced or was disconnected during some servicing.
In this case you will either need to ask your dealer to reset it, which they can by connecting up to the diagnostic system, or you can do it yourself.
I found some instructions for a MZR 2.0, but it worked very similarly, as below, on my CX5 2.2 diesel.
1. Warm up the engine. Turn everything electrical off that you can - radio, A/C etc so there is no/minimal electrical load.
2. Switch the ignition off.
3. Switch ignition to on but dont start engine. Long-press the i-stop OFF switch for 3 s within 5 s after switching the ignition ON.
4. Start the engine.
5. Press the i-stop OFF switch. Verify that the i-stop indicator light (green) flashes and stays flashing. If it does not flash, go back to Step 3.
6. Allow the engine to idle for 10 minutes, or until the i-stop indicator light (green) turns off. Mine didnt stop flashing so after 10 minutes or so i just went to step 7.
7. Switch the engine off. Wait a minute or two.
8. Start the engine. Go for a drive, and check that the i-stop system operates normally. Those with i-stop will know that you may need to drive a mile or two until it activates. Remember that i-stop will not operate when (a) diesel engines are in regen mode, and (b) in some other conditions - see your manual for details. Also, if a new battery was fitted, it may take some time for the new battery to fully charge up before i-stop will start working. Go for a decent drive so it gets fully charged.
9. If i-stop operates as normal, you have successfully reset it.
Cheers!
