Hi All,
As per my name, I have a used Mazda MX5. I've owned it for 18 months and after replacing the battery twice, I realise that it has a battery drain. If it is undriven for a week then the battery will be flat. Mazda spent about 2 hours checking it out but drew a blank. I'm not able to drive at the moment due to surgery, but hope to be out in a few weeks.
The car is garaged at the moment and left on a permanent trickle charge. Do you think that this is my best way forward, or would it be an idea to disconnect the charger periodically. Anyone have any ideas about what may be going on? A mobile auto electrician thought that it may be a software issue, but Mazda said there were no updates re software. It's a mystery!
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Interior light coming on, unnoticed?
Take the bulbs out.
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>> Interior light coming on, unnoticed?
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>> Take the bulbs out.
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Or put your mobile on video mode and shut it in the boot and the glove box.
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Use a multimeter to check the 'dark current'. If you are not familiar with this read the manual and make sure to use the correct lead connections and don't put the leads across the battery! I use a cheap Sealey MM20 and if I start with the 10A range I have to swap the red lead over if I go down to the 200mA range or lower.
Take off the battery earth lead, set the meter. Make sure the ignition is OFF. Start with a 5A-10A range. Connect the meter between the earth lead and the negative battery post to measure the current. If it's going flat in a week the drain could be on a scale of 200mA or a bit more. It should be well under 50mA. I had a Mk2 and whilst it would go flat when unused it took at least 2/3 weeks before it was too weak to start the car.
Once you've established what it is, pull fuses one at a time until the drain drops. Power locking, power windows, interior lights, audio etc.
Most if not all of these will be in the passenger compartment fuse panel. The brake lamp fuse is under the bonnet, it covers the horn as well if it's like mine was, and I think it's live with ignition off so check that one first. I'm sure you'd notice if your brake lamps were on but maybe it can just leak a bit or short.
I'm just telling you what I would do, I'm not any kind of auto electrician so if you know one ask them.
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>> Once you've established what it is, pull fuses one at a time until the drain
>> drops. Power locking, power windows, interior lights, audio etc.
If its a modern car, you'll need to prepare a bit more to find parasitic current drain. The car will need to be "asleep". Which may take 15 minutes. As soon as you open a door, boot or even the bonnet, it will be"awake" again. So you will need to cheat all those interlocks some way.
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That makes sense Z, but if as I inferred it's 25 year old MX-5 there's not much modern about it. It has an ECU but doesn't use CAN and has no OBD2 port if I remember correctly. I had a couple of wires with a bulb that I could poke into various holes in a box under the bonnet for diagnosis.
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Actually I took it to be a 1.8 year 2000 so a Mk2. I suppose he could mean 2 litre 2018 in which case I could have wasted my time - OTH it might still work provided as you say the OP waits for it to shut down.
If it's 2018 it will be an ND1. There was a recall at one time for a battery drain issue related to leaving the cruise control switched on, which should not have drained the battery but did - only on the RF versions I think.
What is it MX5man?
Last edited by: Manatee on Tue 9 Dec 25 at 16:24
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Mazda MX5 - 18 2000 Battery Drain - Duncan
