These instructions apply to the Mazda 3 Mk3 (BM/BN) 2013-2018. For other models, please choose your vehicle here.
Last updated:
If the remote or smart key on your Mazda 3 Mk3 (BM/BN, 2013–2018) only works from up close, or has stopped locking the car, the fob’s coin battery is almost always the cause — and it is a quick change. This guide shows how to swap the key fob battery and what needs a dealer.
First, Rule Out the Battery
A weak fob battery is the number-one reason a Mazda 3 remote becomes unreliable — short range, needing several presses, or hands-free entry/start failing. Most Mazda 3 keys use a CR2025 coin cell.
Replacing the Fob Battery
- Push and hold the release knob/catch and slide out the auxiliary (mechanical) key.
- Insert a small flat screwdriver into the gap and separate the two halves of the case.
- Pull out the button-cell cover and lift out the old CR2025 cell.
- Fit the new cell with the positive (+) side facing upwards.
- Check the O-ring seal is not distorted or displaced (it keeps the key water-resistant), then close the case and refit the auxiliary key.
- Test the remote.
After a battery change the key keeps its programming — no re-pairing needed.
Lost Key or Adding a Spare
The Mazda 3 requires a diagnostic tool (Mazda M-MDS) to program a key, and adding one generally needs at least two existing programmed keys present. A lost or extra key is best handled by a Mazda dealer or an auto-locksmith — there is no simple owner sequence. The home job is limited to renewing the battery in a key that already works. Up to six keys can be registered to the car.
If a Fresh Battery Doesn’t Fix It
- Check the cell type and polarity — a CR2025 fitted the wrong way gives no response.
- Use the auxiliary key to unlock the door, and hold the smart key against the start button to start if its battery is flat.
- Still nothing from any key? A receiver or body fault may be involved — check the code on autodtcs.com.
Frequently Asked Questions
What battery does the Mazda 3 key take?
Most use a CR2025 coin cell. Check the old one when you open the fob to confirm.
Do I need to reprogram after changing the battery?
No — programming is retained. Just fit the CR2025 the right way round, check the O-ring, and test.
Can I program a new Mazda 3 key myself?
No — the Mazda 3 needs the M-MDS tool (and usually two existing keys) to register a key, so a new or replacement key is best coded by a Mazda dealer or locksmith.
How do I start the car if the smart key is dead?
Use the auxiliary key to unlock, then hold the smart key against the start button and press — the car reads the transponder directly.
If the remote stopped working after a battery disconnection, see our Mazda 3 battery disconnect/reconnect guide.
Disclaimer: The information on this page is provided for general guidance only. Always follow your official service manual and safety precautions when working on your vehicle. We are not responsible for errors, omissions, or any damage resulting from the use of this information.
This website is an independent resource and is not affiliated with, endorsed by, or sponsored by Mazda. All trademarks and brand names belong to their respective owners.