Board logo

Mazda 2 alternator or battery problem?
craig1410 - 23/6/16 at 05:42 PM


My wife's 2013 Mazda 2 Tamura (1.3) appears to have either a battery or alternator problem as it is sometimes sluggish to start, sounding like the battery is flat. I just put a voltmeter on the battery not long after it had a 30 minute run and the voltage without any electrical load was 12.4 volts. When I then put the headlights on this dropped to 12.09. I then started the engine and it only went up to around 12.8 until I added in some extra loads such as air con and blower at which point it went up to 13.4v. This still seems a bit low to me as I would expect closer to 14v if the alternator was charging properly. However, I realise it might be some sort of eco-related system to avoid alternator load until the car is braking or whatever. I know my BMW has something like this to only charge the battery when off throttle (I think).

So, the car is under warranty but just curious whether you guys think this is a battery problem or alternator? The battery is a 55AHr and the fluid level is at the upper level (first time I've seen a transparent case on a modern battery). No signs of leaks etc. The alternator looks clean and the belt is tight.

My opinion is that the battery voltage seems low given it just had a 40 minute run and to drop from 12.4 to 12.09 with just headlights seems to indicate a weak battery. Then again, the weird charging behaviour and low charge voltage could indicate a bad alternator (or a bad battery preventing proper charge I guess).

Any thoughts? It'll be getting fixed under warranty in any case so this is largely academic.


britishtrident - 23/6/16 at 06:36 PM

Could be a parastic drain the car rather than the battery or alternator problem parasitic drains are not an unkown on modern Mazda.
Problem with parasitic drains on a computeriesd car is low parasitic draw current is very difficult to trace and if has been going on for a while can seriously damage a modern battery.
Batteries that are very low on charge take a long time to recharge, batteries that fail to start a car the batteriy has bad cell will appear to recharge quickly.

The dealer should have an up to date "smart" battery tester that can test the battery and predict the remaining life even if the battery almost flat otherwise the it would need to be almost re-fully charged and then rested for a few hours before a high current load volt drop test,
If they are up to the mark they can also do an AC voltage ripple test on the alternator and a chargingamp check with a DV clamp ammeter.
Parasitic drain test usually take more time and involve checking the drain through individual fues by measursing the tiny voltage drop accross a fuse carrying current.

[Edited on 23/6/16 by britishtrident]

ian locostzx9rc2 - 23/6/16 at 06:43 PM

Check the voltage again with no load then put the gin on and sidelights and see if the voltage goes below 12 volts after a couple of minutes if it does it's a battery issue
Note if you have a duff or weak battery checking the charge rate isn't normally very accurate .

craig1410 - 18/9/16 at 12:00 AM


I just realised I had never replied to this thread so apologies for that, I was sure I had...

Unfortunately the car is no longer under warranty and the problem re-occurred causing my wife to become stranded at the local supermarket. I had to go and rescue her with jump leads.

I found an alternator on ebay for £29 so decided to just get that and fit it to see if that was the cause of the problem. Initially it looked promising as I saw over 14v output but since then the car has started to play up again and is showing signs of sluggish cranking again. I also noticed tonight that the headlights looked a bit "yellow" when I saw my wife driving past me while I was walking our dog.

From a bit of research I can see that this is an externally regulated alternator where the PCM (Power Control Module) within the engine ECU is responsible for measuring things like intake air temperature, coolant temperature and electrical loads before deciding what charge level is desirable. It controls this by measuring alternator output voltage and then sending back a PWM (Pulse Width Modulated) signal to the alternator to control field current strength. I'm pretty sure the alternator is working fine but for some reason (faulty ECU, wiring or sensors) the PWM signal is not correct. I found some technical info on a Mazda MX5 charging system which looked very similar and it said the voltage on the PWM wire should be between 3 and 8 volts and I measured 3.82v with a battery voltage of just over 13v.

So, does anyone out there have any Mazda technical manuals or wiring diagrams or anything else which might help me to diagnose this problem? I'd hate to think I'm going to need a new engine ECU and of course if it comes to that I'll be on Mazda's case looking for goodwill towards the cost. I'm hoping it's maybe just a dodgy bit of wiring or a failed sensor but I need schematics to try to figure it out. The battery charge light illuminated before being started and goes out once started and there is no engine check light so I guess no fault codes.

Thanks, and apologies once again for not responding to this thread sooner.

britishtrident - 18/9/16 at 05:03 AM

On MX5's I have worked on the alternator supplies a duty cycle signal to the ecu so the engine can predict the engine load but the charging control is entirely integral to the alternator and independant of the ECU. The standard Denso 4 wire alternator supplies a square wave to the ECU the duty cycle of which tells the ECU to adjust the idle speed/ A 50 perecent duty cycle = zero electrical load and zero duty cycle tells the ECU the alternator is operating at maximum full field output. This type of alternator normally has a back cover pressed from shiny sheet aluminium. On this type rectifier failure is not unknown but it is very easy to repair.
On this type of alternator the 4 wires are:
B+ main feed cable,
Warning Light,
Duty Cycle
Battery Sense

However some Mazdas I believe the Smart Charging system is as fitted to some Fords and is controlled by the ECU

Be aware that the system used by Ford is not only Smart charge system arangement for example GM use a very different system. However Ford and Mazda have very close links,

[Edited on 18/9/16 by britishtrident]

craig1410 - 18/9/16 at 10:38 AM


My alternator is a Mitsubishi A2TG1391 equivalent to Lucas LRA03482 or Delco DRA0639. I tried to find a spec sheet but no joy so far. I did find a catalogue listing a new diode pack and regulator for this alternator and it referred to the connections on the 3-pin plug as as P and D which corresponds to a diagram I saw elsewhere for a smart- charge system. Also Mazda and Ford share a lot of parts as you know.

The schematic I saw showed that the ECU sends a duty cycle (Pulse Width Modulated) square wave to the alternator and this is applied across a capacitor to ground. That creates a steady voltage between 3 and 8 volts which is applied to the base of a transistor which in turn controls the field current in the alternator and thus the output power. The rest of the alternator is standard 6 diode rectification etc. The alternator sends a signal back to the ECU from the middle of one of the diode pairs. I expect this is to measure output power.

So, I'm pretty sure this is a smart charge type alternator but I need to figure out which sensors it uses and where they are located so that I can check all the wiring involved in the control of the alternator. I believe the ECU is on top of the engine.

I should probably get myself an up to date fault code scanner. I used to have one which could also read sensor values but I gave it away to someone a while back. I had intended to get a better one but never got around to it. Recommendations welcome, ideally one I can use with both my BMW 535d and the Mazda 2 and ideally one that can be used with an iPhone via bluetooth or WiFi.

Thanks again,

craig1410 - 12/11/16 at 05:17 PM

Just an update on this saga. I've done two things since my last update.

1. I bought a battery analyser. It's a Foxwell BT100 Pro which I got on Amazon for £36.50 ( ) This device does a conductance test which is a bit different to a high current load test but is the technique that more expensive testers use to predict battery life and performance. Basically you tell it the rated CCA of the battery and it will tell you the percentage of that rated value still available. For my original battery it was rated at 355 CCA but was only reading 249 CCA. Also, even though I had just driven for 30 mins in the car to Halfords and back today, it was saying it was only 85% charged.

2. I bought a new Yuasa YBX5005 (Halfords HSB005) battery. This is branded as a 'Silver' battery but actually it's a calcium based battery as far as I can tell. It is regarded as a pretty high quality battery though and with my trade card I got it for £79.99. It's available online a bit cheaper than that but I wanted it today. While there I got Halfords to test my battery using their tester which was a Yuasa branded tester and to my surprise it said the battery was in a good state of health but just needed to be recharged. They estimated CCA at 399A with off-load voltage of 12.35V and 9.81V under cranking. He also did an alternator test and read 13.03V off load and 13.84V under load so that was fine too. The guy didn't have any advice to offer really which was no surprise as it was a bit of a mystery. However, why would the battery not be fully charged having just driven 15 minutes to Halfords and having been used daily for decent length journeys prior to that. Also, why is it when I notice the car is cranking sluggishly and put it on the mains powered charger, that is seems to charge in an hour or two instead of taking 5-10 hours as you would expect for a 55Ah battery being charged from a 6A charger? Also, when charging from the mains charger at 6A the terminal voltage is going to 14.7V or so which seems very high for such a low charge rate.


I believe the battery is faulty and is not taking a charge. Whether it is sulphation of electrodes or whatever, I don't believe it is storing anywhere near the level of energy it should be. I think the smart alternator on the car is thinking, based on the terminal voltage, that the battery is fully charged but in reality it only has a fraction of the energy stored which it should have. The same is true of the main charger which is going into 'float' mode too soon.

So, I have now installed my new Yuasa battery and my tester is reading 581CCA and 12.61V which it considers to be 100% state of charge. At idle the car is initially running at above 14V but after a short time it drops back to just over 13V and then after a bit longer it drops back again to around 12.8V. This is the behaviour I saw before which led me to replace the alternator but I now think that maybe this is actually normal. If I turn on headlights and rear heater the voltage goes back up to over 14V and if I remove the load again it gradually drops back down again to 13V and a bit below. When you consider that applying 14.7V from my mains charger is only pushing 6A into the battery then it's understandable why the car's ECU is thinking the battery is charged when in fact it is not. I believe the ECU is then backing off the load on the alternator to improve fuel economy and to avoid over-charging the battery. It's hard to be sure without knowing the smart charging profile programmed into the ECU but it seems reasonable that when there is no significant electrical load AND the battery voltage is good, then why keep pulling power from the alternator?

So, lets see how we get on over the next few weeks with the new battery. I've got a baseline reading from my analyser and I'll test it again in a week or two and see how it's doing. Hopefully it will solve the problem but I'll be sure to update this thread if not.


Vicky131082 - 13/3/19 at 08:11 PM

Hi craig, Iím having the same problems with my Mazda 2 Tamura 13 plate. Driving me crazy 🥴 just wondering if you ever solved the problem? Iíve changed the battery 3 times, changed the alternator. Itís been in the battery centre 4 times with no battery drain found. It drains every 3 weeks or so or less sometimes. If you can help in anyway, that would be fab. Thanks Vicky

[Edited on 13/3/19 by Vicky131082]

Angel Acevedo - 13/3/19 at 10:14 PM

Thereīs not much science to it.
You need a multimeter with an Amp measuring setting capable of 10 amp at least and a little bit of patience.
Finding parasitic draw is not much of a problem, fixing it can be more dedicated depending on what you find...
There are severa vids on youtube about finding parasitic draw..

craig1410 - 14/3/19 at 12:32 AM

Originally posted by Vicky131082
Hi craig, Iím having the same problems with my Mazda 2 Tamura 13 plate. Driving me crazy 🥴 just wondering if you ever solved the problem? Iíve changed the battery 3 times, changed the alternator. Itís been in the battery centre 4 times with no battery drain found. It drains every 3 weeks or so or less sometimes. If you can help in anyway, that would be fab. Thanks Vicky

[Edited on 13/3/19 by Vicky131082]

Hi Vicky,
Yes the new battery solved the problem completely but you need to get a good quality battery such as the one I mentioned in my above post. The ďsmart chargingĒ system on the Mazda requires a battery which can handle the charging profile.

Halfords themselves told me my old battery was fine and were very sceptical about whether a new battery would solve the problem. I chose to follow my gut, 35 years of electronics experience and an electronics degree rather than believe a battery tester used by someone who probably had 30 minutes training on how to use it. No disrespect intended to the well meaning Halfords employee who was trying to save me buying a new battery he didnít think I needed...

We donít still own the Mazda as we sold it in Sep Ď18 but it never had a single problem after I replaced the battery (almost 2 years). Since then I solved all sorts of random electronics glitches on my BMW 535d by replacing the battery despite my battery tester saying the battery is still in 60% health. I had warnings about my suspension levelling system, false positives for tyre pressure sensors, sluggish starting etc. Changed the battery and no issues for over 6 months!

Finally, I have heard from several Mazda 2 owners (either 2 or 3) who have had the same issues and after reading my post above have successfully solved their battery/charging problems.

I hope this helps as I know how frustrating this problem can be. Good luck!

Vicky131082 - 14/3/19 at 06:36 PM

Thank you so much for replying, will definitely be buying the same battery as you mentioned at the weekend. 😊 thanks once again