Help Me Fix My Expensive Paperweight

Technical Area Electrics & ICE
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  1. My model of MX-5 is: ND 2.0 RF 2017
  2. I’m based near: Nottingham
  3. I’m looking for technical help.

Hello all, I’m hoping that the internet may be able to point me in the right direction, as currently my MX5 works as a very expensive paperweight.

Three weeks ago my window regulator and motor packed in (super irritating trying to get reasonably priced parts BTW).

So my car sat for a two weeks. Come Tuesday I go to start the car to take it to the garage and nothing… the Start/Stop button flashes orange at me, no other signs of life.

I replace the key fob battery, no dice.
Local garage pops over with a jump start kit and a OBDII reader, the car is throwing errors relating to the battery, which when cleared, solves the issue, green light on the Start/Stop button.

I get the car to the garage, turn it off, exit the vehicle and the the Start button flashes orange at me again. We test the battery and it has two dead cells, we replace the offending battery but the behaviour returns despite the battery reading 12.0-12.1 volts.

Side note, the dash intermittently flashes the “Roof is Open” indicator. Although i’m not convinced that this isn’t a separate issue, just opportune timing. The window regulator and motor were successfully replaced.

Does anyone know what could be stopping the car from starting? Despite the battery change? Any pointers/tips?

Cheers

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IMG_20220519_1105541920×1440 336 KB

The offending car

3

Small update: the icon flashing on the dashboard (intermittently) is infact the Active Bonnet System light.

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I can tell you that 12-12.1 volts is not good from memory I think you should have a reading of at least 12.6 with the engine turned off

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5

I have just checked and a reading of 12 volts indicates that your battery is only 50 percent charged

6

Is this with a multimeter hooked up to the battery?

7

Thank you for checking. Surely the car should still fire up with the battery at 50% charge though?

Ordered myself a charger though, will see what happens.

8

It’s probably best to think of the battery as being either fully charged or fully discharged.

11.8V is considered fully discharged.

12.6V is considered fully charged.

So there’s only 0.8 volts between a battery that can definitely start a car and one that definitely can’t, so you can see how 12.0/12.1 could be too low to start a car.

(admittedly some batteries charge to 12.7+ but the above still stands as a rough guide).

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Excellent stuff, thank you. So potentially I just need to charge the battery and my woes will be at an end? Any thoughts on whether this could potentially cause the flashing Active Bonnet System warning light on the dash? If the battery is too low?

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I couldn’t comment about the active bonnet system as I don’t own an ND.

Unfortunately I have had a lot of experience with flat batteries though :smiley:

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11

The charger or better still a smart charger is a good idea.

How long are you leaving it for for it to not start. (after the new battery)?

It was a known issue with early RF models that the battery would discharge more quickly if the cruise control was left on. Apparently there was a current flow even though the ignition was off.

So my best advice is check that the cruise is off and pop the car on a smart charger every week or so.
Experience has shown that with both ND1 and ND2, two weeks of standing is pushing the limits of the battery. Particularly if you keep unlocking the doors to ‘play’ with the car but not use it.
:heart:

2 Likes
12

A low battery was the cause of my daily driver (not Mazda) throwing codes up and even going into limp mode. Traction control, ABS and engine management lights all on. Codes also pointed to throttle position sensor at fault, no such problem it was the battery dying.
Get a charger and keep it topped up if the car has little use. Clear any codes and get yourself a battery condition test gizmo, about £20 of eBay, plenty there and do the job ok.

1 Like
13

I can’t comment on the active bonnet either, but there are similar issues with the NC and warning lights after a battery change (flat battery), so don’t rule it out.

The fact that a 7 year old car was stood for two weeks , then I can well imagine that the battery was heading towards end of life, and especially over winter.

As regards the replacement, who knows how long it’s been stood on the motor spares floor.
Without a shadow of a doubt, a good solid charge or a decent run would be my first form of attack.

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The new battery was in for about 3 minutes before it refused to start again. Yes, ordered a smart charger. I don’t think I have ever used Cruise Control, so that won’t be the issue :smiley:

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Thank you :slight_smile:

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what voltage was the new battery putting out or are you just assuming it was a good battery

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New battery was putting out 12.0-12.1 volts after being put in. So judging by the comments, I assume it may have been sat for a while?

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A previous owner may have so I would check just in case. It is a known problem and will cost nothing to check.
Hope you get sorted soon.
:heart:

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19

I’ll check but had this car for nearly 5 years now! :smiley:

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20

Thanks Keat, good notes! Seems like it may be the battery still! At least it isn’t ECU death :smiley: