FWIW I-stop rarely stops my engine for very long. I never time it but I doubt it’s ever longer than 30s and touching virtually any control will start the engine again.
Gave up worrying about whether it operates or not. There is a setting in the displays somewhere to get statistics on how much it’s saved; if you have nothing better to do…
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How can you possibly mess anything up or invalidate your warranty by taking the negative battery terminal off, waiting 20 minutes and reattaching?
You asked for help and it appears you were never willing to actually try anything. Very strange.
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I thought you had to mess about with the I-stop button which would then alter settings in the ECU. If it’s just a matter of taking the negative battery terminal off I will give it a try in the next couple of days. Thanks. I will try anything but am wary of doing anything that the service people can detect with their OBD computers. I am super nervous about the dealership telling me to nick off because I tampered with the ECU or other bits. Taking the terminal off is a no brainer (says me with a little brain 
) so I will give it a go. Sorry if I gave you the wrong impression.
EDIT: Will all radio, time and phone connection data be lost if I disconnect the battery?
As you (may) know, if you use a Battery Minder on the MX5 with i-Stop, it really doesn’t like it.
To mitigate, do not put charge leads across the battery, positive to battery + post is OK but negative to ground on the body somewhere is recommended. However, this did not work for me as i-Stop stopped working (again).
This time I also got a “Battery Management Malfunction” warning light and a little yellow triangle along with an i-Stop Not Working message.
After using the battery minder, battery voltage was 12.57v. It was new 12 months ago.
Before, I had used instructions found on the web but this time, it wouldn’t clear the messages so I investigated further and found a Malaysian video that showed step-by-step instructions. Although it wasn’t an MX5 that was being cleared, the instructions are almost the same.
I will post a link to the video below, but here are the differences I noticed.
After reconnecting the negative terminal and waiting 30 seconds before reattaching the sensor, I shut the bonnet (unlike the video instructions). This is because the MX5 has a bonnet switch that tells the car it’s in maintenance mode and it stops i-stop from working (sensible when you think of it, a mechanic will not want to be working on an engine that keeps stopping!).
Secondly, in the video, it says the i-Stop light turns green - on my MX5 it is orange or off. Read “i-Stop off” instead of “i-Stop flashing green” in the video.
Otherwise, it all reset perfectly and a short drive and i-Stop was doing what it should do - whereas using previous instructions I’d found, it could take a couple of hundred miles before starting to work again. I believe the secret of the success of this video is disconnecting the sensor plug from the voltage sensor on the (-) battery lead allowing it to reset.
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So do you disconnect just the sensor lead or the whole negative terminal? Also, do you lose all radio, bluetooth and time settings?
For the ‘simple’ solution that has worked for many just take off the whole negative terminal, then, in 20 minutes put it back.
The only things you lose are your trip readings, the are all reset to zero.
I and a neighbour have done this and it worked every time.
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Just lose trip, as Malc states.
I separated the sensor from the neg lead as well.
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Thanks, I will give it a go. Thanks to all who have responded. I really greatly appeciate it!
The current sensor connector should always be disconnected before removing the negative battery cable and reconnected after. Leaving it connected can allow it to detect a current surge during disconnection and reconnection resulting in the system incorrectly calculating the battery state of charge.
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Okay…I know where that lead is because I saw it when I charged the car with the smart charger. I will gently pry it out before disconnecting.
Many thanks to all who have responded.
On I-Stop just to share my experience (in short the 20min disconnect worked to reset the system and get it working).
I-Stop had not even worked once since I bought my new MX5 6 weeks ago. Used at weekends 400 miles on the clock and weekly CTEK charge. (It had been a showroom model which I understand had also been on periodic charge -CTEK used there also).
I could never get the battery condition to light (except when back from a drive and actively connected to the charger). As soon as I took off charge and started the engine the battery icon would go out, and not even a 30-45min drive made any difference.
(I phoned the dealer who suggested that after taking it off charge it would still need to be driven for a few miles to get the system working, but I already knew that never helped so I was set to take the car in to the dealer to fix and confirm no other battery issue.)
Found this thread and read about the current sensor not updating (BATT_SOC) but wasnt keen on trying a complicated full reset (incl steering angle reset etc).
So followed Mad_Malc, simply disconnected the 10mm main clamp from the negative terminal (ie the entire module incl current sensor module and didnt disconnect the 12mm negative lead …as that was tightly bound with the leads for the Current Sensor).
Reconnected it 20mins later. Switched on car (without ignition) and system said ready incl the Battery icon. That stopped as soon as I started the engine but about 2-3miles down the road came back to “Ready” and I was I-stopping all the way home. The longest I-Stop stopped for was 2mins (before it restarted the engine).
Not that I’m fanatical about these Start-Stop systems but I did want to be sure my new car was at least working as it should.
Thanks to those on forum who’ve taken the time to share their experience & advice. Mazdas have at least as many quirks as other brands but I’m certainly enjoying the MX5.
Chris
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The simple fix is always the best fix.
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Just to chip in here,
My ND2 is 8 months old from brand new with 1500 miles on the clock.
I-stop has been working fine until about two weeks ago when I noticed it hadn’t cut in for quite a while and coincidentally with the start of the cold weather here in Derbyshire, so I thought I’d start by reading the manual (unusual for me 
), I have to say I am amazed at how many things prevent I-stop from working under “normal use”.
Amongst the reasons are, steering not straight ahead, moving the steering after coming to a stop, temperature variation between the outside and inside of the car above a “certain amount”, having the temperature control set to minimum or maximum, battery condition, battery charge, driver door open, bonnet open, ambient temperature.
The other thing I have found confusing but now get is that, on the dash the word istop illuminates in amber when you first turn the ignition on and then goes off, according to the manual this amber actuation shows the system is working correctly and comes on in green when it activates during driving.
Now, I had a Volvo V60 from new for about 6 years and the Volvo equivalent of istop was unbelievably erratic in operation and wouldn’t work at all if the outside temperature was below 5 degrees which is confirmed in the Volvo manual. I am assuming that the reference in the Mazda manual re ambient temperature is the same as Volvos 5 degrees but Mazda won’t put a number on it.
Regards
Clive
After so sadly selling both our Roadster & 2002 Sport as many know s few weeks back to take delivery of our new built Suzuki Sport Turbo 1400cc Hybrid, I’ve done the unthinkable and let it’s Istop do it’s evil work. Or better put, it’s less bother to switch it off on the dash and just let it carry on as switching off only lasts fot that journey. The Swift’s Istop must be powered from the main battery, which also tops up the hybrid pack, as it never runs out of juice as there is only one main under bonnet battery as far as I can tell…the 48 volt hybrid being buried under the floor pan. Why some car manufacturers insist on over engineering these infernal toys defeats me. Being a ltd production Sport still built in Japan, this car has been 100% fault free with over 900 miles on now. C/mon Mazda…wakey wakey chaps. Oh…and you can buy mica yellow ones!
( Cancer in remission BTW, heart fail stable, and I’m all good just now) Just enjoying the finest engineered small hatch I’ve ever had. By God it bloody goes! The extra leccy 50-odd lb ft is real. Take care my old friends.
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Hi Scottishfiver,
Great to hear from you, and I’m really glad that you are ‘all good’ at the moment.
I miss your amusing comments on the forum, as I’m sure lots of others on here also do!
Look after yourself.
JMK
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This is a long thread and it’s probably been said somewhere, but there will be a doodah to measure the charge going in and out of the battery somewhere. If the battery is charged e.g. by a battery maintainer connected directly to the battery terminals, it won’t go through said doodah and the charge going in will not be detected.
Glad I’m not plagued with it TBH.
That’s the little fiddly bit on the negative terminal. It should know about dark current.
This is our 2016 iStop Mazda3 battery, much the same system as in the early NDs.
HOWEVER, it dos not measure self discharge inside the battery, only normal usage and charge control. The system has to guess about possible self discharge.
These batteries are quite good in this respect with not much self discharge, they are certainly a lot better than traditional lead acids. Normal driving and the usual charging cycles will swamp any of these minor effects.
Only when the car is not used for months might self-discharge become significant. I expect there might be some clever algorithm to take account of this to fiddle the sums it has to do, but the simple solution is an occasional top up.
During the first lockdown when we went nowhere I charged our 2016 Mazda3 iStop battery in the car twice several weeks apart. It is still on the same battery.
Thank you Sir. Get Bone Scan results soon, and soft tissue organic scan results soon as well. Must say a new car has pepped me u p…do a lot more ad hoc pleasure coffee & cake trips. Before…it was “which battery is gonna go?” 
These wee Suzukis are something but the one we got is a pure riot.
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Good to see that my revival of this thread has helped others and me as well. The 20 minute disconnect did the trick nicely. Many thanks to Mad_Malc for suggesting the fix. So much for the dealer wanting to keep the car for days to perform an analysis and reset. As Mad_Malc has written above, the simple fix is always the best fix.
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Some time ago, Stop/Start had decided to stop stop/starting (!) so I took the decision to CTEK charge the battery and reset the stop/start, prompted by the posts above.
I opened the door, pulled the bonnet release, shut the door, walked around the front, door locked. Opened bonnet, disconnected battery negative, connected CTEK, shut bonnet.
All OK, CTEK charged and then went to “maintain”, after 24 hours. Great! Went to car, “ah”, key won’t open the door with no battery connected. HeadSlap. Teased the key cover off, damned tight, got the key out of the fob and unlocked the door - first time in 5 years! Can confirm the key fits, at least.
Connected the battery and went for a drive. Within a half-mile, the engine, battery and aircon icons all turned blue and the stop/start started working at the next junction. Result. Before, I’ve had to do all sorts of fiddles to reset the stop/start, this time it was done just by disconnecting the battery. Great tip from Mad_Malc.
Weird thing is . . . On the i-ELoop screen where you see the battery charging/discharging (actually the capacitor, but whatever) I have never noticed the wheels on the car graphic going around as you drive along. You learn something every day. I was today years old when I discovered that.
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