These instructions apply to the Hyundai i20 Mk3 (BC3) 2020-Present. For other models, please choose your vehicle here.
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The Hyundai i20 (Mk3/BC3, 2020–Present) offers keyless entry and a START/STOP button on Premium and Ultimate trims, while lower specs keep a turn-key barrel. If the Smart Key’s CR2032 cell goes flat the buttons and proximity sensing stop working, but the i20 can still read the key when you press the fob against the start button — and turn-key cars are unaffected once you use the blade.
Start a Smart Key i20 with a dead fob
For an i20 with the keyless Smart Key and a dash-mounted START/STOP button:
- Unlock and enter the car with the emergency blade (next section), then sit in the driver’s seat.
- Keep your foot firmly on the brake pedal.
- Hold the Smart Key flat against the START/STOP button so the body of the fob touches it.
- Press the START/STOP button while keeping the fob pressed in place.
- The short-range reader behind the button wakes the transponder and the engine starts.
Turn-key i20 — the blade starts it normally
SE Connect and other lower trims use a flip key and an ignition barrel. A dead coin cell only stops the remote-lock buttons; unlock the door with the blade, insert it in the barrel and start the engine as you always would. The barrel reads the transponder directly, so the flat cell makes no difference.
Unlock the i20 with the emergency key blade
- Press the release on the back of the Smart Key and slide out the metal emergency blade.
- Insert the blade into the lock slot on the driver’s door handle and turn to unlock.
- The alarm may sound briefly — it stops once you start the engine and the key is verified.
Why a flat fob still starts the i20
The coin cell drives only the remote buttons and the proximity broadcast for hands-free unlock and start. The engine-authorisation chip is a passive RFID transponder that draws its power from the car — the coil behind the START/STOP button, or the ignition barrel on bladed cars. Since that chip carries no battery, the immobiliser still recognises the key even when the fob is dead.
Replace the fob battery
The i20 Mk3 Smart Key takes one CR2032 3V lithium coin cell. Remove the emergency blade, then prise the case apart at the seam with the blade tip or a coin. Swap the cell, keeping the + side oriented the same way, and snap the case shut. Remote locking and keyless start work again at once. A quality cell lasts roughly two to three years.
Frequently Asked Questions
How do I know if my i20 is keyless?
Keyless i20s have a START/STOP button on the dash and lock/unlock by touch. If yours has a barrel you twist a key in, it is a turn-key car and only needs the blade.
Do I press the fob hard against the button?
Firm contact is enough — hold the body of the fob flat against the START/STOP button, keep the brake down, and push the button.
Can I lock the i20 again with a dead fob?
Yes — use the emergency blade in the driver’s door to lock it mechanically until you fit a new CR2032.
Why did the alarm go off when I unlocked it by hand?
Mechanical unlocking trips the alarm until the transponder is read. Starting the engine cancels it.
What battery does the i20 Smart Key use?
One CR2032 3V lithium coin cell, sold at any supermarket or hardware store.
If a dashboard warning stayed lit after the no-start, check it on autodtcs.com to be sure it was just the fob and not an immobiliser code.
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.
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