Author Topic: Key fob won't work after changing battery  (Read 484 times)

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Offline Angry Kittens

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Key fob won't work after changing battery
« on: November 01, 2018, 11:37:59 PM »
Hi all,

I have a 2016 Mazda 3 SEL-NAV, been going almost 2 years now, recently had a warning for low key battery, started using the second fob and got the warning on that to.

Changed the battery in one of the fobs today, it will unlock & lock the car, start the engine (button start but not keyless entry, still press a button to unlock) for about 1 minute. After the battery has been in a minute it will no longer open the car. The red light on the fob still flashes, if I reseat the battery it again works for a minute then stops working.

The manual simply says for new batteries in key fobs go to the dealer, not sure if they would cover it under warranty, I think less than 2 years is poor for a battery.

Any ideas? My guess would be I need to resync the key, but I'm not exactly sure how to do that, every post I find mentions putting the key in the ignition, so i guess for older models and not button starts. No videos showing how to take that model of key apart mention any steps after putting it back together.

I did think I have a dodgy battery, but doesn't explain why it works for a bit, continues to light the key up, and works again after reseating.

Appreciate any help here, last hope before I go to the dealership I guess...

Offline StevenRB45

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Re: Key fob won't work after changing battery
« Reply #1 on: November 02, 2018, 05:14:51 AM »
All I can suggest is trying a good quality battery.

I had intermittent and moderately annoying key fob issues on my gen 2 for years on and off. Was changing the battery every six months, thought the boards in the fob might have a loose connection after a while. e.t.c. Basically would work fine for a bit, then after a while it would need pressed twice, then wouldn't work at all but dismantling the key and re-installing battery made it work again.

In the end I found somewhere on line that did Duracell button batteries rather than the weird off brand ones all the local shops did and all my issues stopped.

Offline hanix

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Re: Key fob won't work after changing battery
« Reply #2 on: November 02, 2018, 08:30:24 AM »
The batteries are available on Amazon for a couple of quid for two. Most manufacturers recommend changing them every year.

Offline FemGearHead

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Re: Key fob won't work after changing battery
« Reply #3 on: November 02, 2018, 10:38:21 AM »
I too have a 2016 and I've had to replace the battery in my fob twice now. I was amazed how quickly these suckers eat thru batteries, since I never once replaced the battery on my 04 fob in the 12 years I had that car.

It was explained to me that proximity keys are constantly "on" and therefore, eat up batteries like the cookie monster devours cookies. I've been lucky that the dealer where I bought my car, will replace the battery at no charge for me. I just have to find a few minutes to go in and ask for a new one.
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Offline Engineer Andy

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Re: Key fob won't work after changing battery
« Reply #4 on: November 03, 2018, 08:10:34 PM »
I too have a 2016 and I've had to replace the battery in my fob twice now. I was amazed how quickly these suckers eat thru batteries, since I never once replaced the battery on my 04 fob in the 12 years I had that car.

It was explained to me that proximity keys are constantly "on" and therefore, eat up batteries like the cookie monster devours cookies. I've been lucky that the dealer where I bought my car, will replace the battery at no charge for me. I just have to find a few minutes to go in and ask for a new one.

Seems very odd - maybe all this new 'keyless entry' tech is draining the battery more, especially if the keys are reasonably close to the car when at home or work by it interacting with the car.  Like with you, my 12yo Mazda3's key fobs are on the original batteries (had the car from new) - and that's me only using one of them (the other does work - I've used it by mistake a few times each year) 99% of the time as well.  Keyless entry tech was the solution to a problem that never existed, and which created a new (very bad) one of its own - criminals using scanners to intercept the signal and use it to open your car.

You may find that putting your keys in a (quality) Faraday bag to block the signal when you're not using it helps both keep the battery going longer and stops thieves.

Offline Willpower

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Re: Key fob won't work after changing battery
« Reply #5 on: November 03, 2018, 08:35:12 PM »



My 2004 Gen 1 original keyfob battery is still working. Used every day. The 2nd fob is only ever used when I leave the keys with the car for servicing.  A lot of companies are moving away from keyless entry because of the problems mentioned above.
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Offline misar

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Re: Key fob won't work after changing battery
« Reply #6 on: November 03, 2018, 09:10:08 PM »
As already noted several times the key (sorry!) factor in battery life of these fobs is keyless entry. Unlike normal remote only fobs this requires a permanently on radio (at least on my Gen 2) so that you can walk up to the car with the fob in a pocket or bag and open a door or the boot by pressing a button on the car.

I have never been able to understand why they didn't fit an on/off switch to use when it is away from the car for long periods. This would greatly reduce battery drain and also avoid the widely reported key hacking on your driveway scams.

Incidentally I totally disagree with Engineer Andy. I also thought keyless was pointless until I happened to buy a model with it as standard. I soon found how convenient it is and after all these years would really miss it.


« Last Edit: November 03, 2018, 09:39:41 PM by misar »

Offline Engineer Andy

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Re: Key fob won't work after changing battery
« Reply #7 on: November 04, 2018, 01:35:49 PM »
As already noted several times the key (sorry!) factor in battery life of these fobs is keyless entry. Unlike normal remote only fobs this requires a permanently on radio (at least on my Gen 2) so that you can walk up to the car with the fob in a pocket or bag and open a door or the boot by pressing a button on the car.

I have never been able to understand why they didn't fit an on/off switch to use when it is away from the car for long periods. This would greatly reduce battery drain and also avoid the widely reported key hacking on your driveway scams.

Incidentally I totally disagree with Engineer Andy. I also thought keyless was pointless until I happened to buy a model with it as standard. I soon found how convenient it is and after all these years would really miss it.

Fair enough, but what can you do with keyless entry that you can't with the blipper keys?  You walk up to the car, it's now unlocked, but you still have to open the door or boot lid, so you still need to put those pesky shopping bags or box down to open the car door/boot.  Takes me 0.5 sec to reach in my pocket (after putting the bags down) to press the blipper first.  Saved myself £££ on replacement fob batteries or the fobs (given they are far more susceptible to faults generally - some nowadays cost £000s to replace), and significantly reduced the risk of my car being either broken into or stolen.

The other problem is that, unless the car's lights flash or it makes a noise when you walk away, how do you know it has locked the door?  If you then walk up to the car to check, it will unlock it, and it seems rather a pallather for the driver to walk far enough away and get the passenger (if they have one) to check the door is locked, and will that activate the alarm/immobiliser?  The only related invention that is perhaps useful in that regard are the sensors (once the car is unlocked) that detect your foot under the boot so it opens it for you.

I agree though that on the keyless fobs, there should be an on/off switch to conserve battery life, though that's yet another point of failure, as slider switches can be unreliable - I've had many fail on headphones, USB sticks (locks) AV remote controls and equipment prior to press-type switches.

Offline misar

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Re: Key fob won't work after changing battery
« Reply #8 on: November 04, 2018, 02:06:45 PM »
The big change was moving from old fashioned manual locks to electric locks with a remote. Most of your concerns start there - even hacking the remote signal - and keyless is just another small step along the non-essential complexity route (about which we probably agree).

For what its worth, with the Mazda keyless you can hear the locks operate and the car lights flash just like using a remote (which the fob does as well if you prefer). With almost any car you still need to use the door handle and pressing a button on the handle at the same time is about as convenient as it gets - except for a few exotica with power door opening/closing as well!
 

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Re: Key fob won't work after changing battery
« Reply #9 on: November 04, 2018, 02:12:54 PM »
I was having my oil changed on Friday at my mechanic and I mentioned this thread to him. He said to think of the new key fobs like this - it's like they are constantly looking for wifi. He said it's suggested by Mazda to replace your battery every 8 months or so.
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Re: Key fob won't work after changing battery
« Reply #10 on: November 07, 2018, 09:39:26 PM »
All I can suggest is trying a good quality battery.

I had intermittent and moderately annoying key fob issues on my gen 2 for years on and off. Was changing the battery every six months, thought the boards in the fob might have a loose connection after a while. e.t.c. Basically would work fine for a bit, then after a while it would need pressed twice, then wouldn't work at all but dismantling the key and re-installing battery made it work again.

In the end I found somewhere on line that did Duracell button batteries rather than the weird off brand ones all the local shops did and all my issues stopped.

I've had similar issues with cheapo button cells. The garage I used to go to would always replace the battery in the keyless fob every time I took my car in (charging £4 a pop i might add!). I'd always start having intermittent issues about a couple of months later, having to press twice / less range etc. I always replace it myself now with a decent brand and don't have issues any more.

Something else a mechanic also once told me: "don't keep your keys and your mobile phone in the same pocket, it'll wear the fob battery out quicker"...not sure how much truth there is in it but I do it anyway ;D

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Re: Key fob won't work after changing battery
« Reply #10 on: November 07, 2018, 09:39:26 PM »