Start the Car With a Dead Key Fob Battery

Last updated: June 10, 2026

The SEAT Ibiza Mk5 (KJ, 2017–Present) is offered with KESSY keyless entry and go on FR and higher trims, while many SE and base cars keep a conventional remote with a start button. Either way, a dead fob battery is rarely the dead end it feels like: the fob carries a battery-free transponder chip, and SEAT built an emergency reader into the steering column so the immobiliser can still read the key. Get in with the hidden blade, hold the fob to the right spot, and the supermini starts.

This guide is for the fifth-generation Ibiza on the MQB-A0 platform. If your Ibiza has a plain turn-key barrel rather than keyless go, the cut blade in the fob starts it directly — the coin cell only powers the remote-locking buttons, so a flat battery never stops you driving.

Start the keyless Ibiza with a dead fob

1. Get into the driver’s seat with the fob and close the door so the cabin antenna can pick up the key.
2. Press and hold the brake pedal — the Ibiza will not start without it.
3. Press the START/STOP button once. A “key not found” message appears in the cluster.
4. Hold the fob flat against the right-hand trim of the steering column, level with the small KESSY logo just below the wiper stalk. That spot sits over the emergency antenna, where a lock barrel would be on a non-keyless car.
5. Keep the fob pressed there and push START/STOP again with the brake down. The transponder is read through the antenna and the engine fires.

Unlock the doors with the emergency key blade

1. Release the catch on the fob and slide out the metal emergency blade.
2. At the driver’s door handle, push the blade tip into the slot under the lock cover and lever the cover off upward, exposing the lock cylinder.
3. Turn the blade in the lock to open the door. Expect the alarm to sound — it stops when you start the car.
4. Clip the handle cover back over the lock once you are in.

Why this works — the immobiliser note

The Ibiza’s smart key combines a battery-powered radio for keyless entry with a passive RFID transponder that is powered wirelessly by the car’s antenna coil. When the coin cell goes flat, the radio stops but the transponder still works the moment it is held within a few centimetres of the KESSY reader. The steering-column position is simply the closest the chip can get to that coil, which is why the engine starts there and nowhere else in the cabin.

Replace the fob battery

The Mk5 Ibiza fob normally takes a CR2032 3V lithium coin cell, though some early cars shipped with the thinner CR2025 — always check the cell you remove before buying a replacement, as the two are not interchangeable. Pull the emergency blade out first, split the fob along the seam it leaves, swap the cell with the + face up, and snap it shut. Keyless Ibizas drain fobs faster than non-keyless ones because the car and key poll each other constantly, so plan on a yearly change.

Frequently Asked Questions

Where is the emergency reader on the Ibiza Mk5? On the right side of the steering column under the wiper stalk, marked with a Wi-Fi-style KESSY icon. Hold the fob there after the first button press.

How do I know if my Ibiza is keyless? If you can unlock and start it without taking the key out of your pocket, it has KESSY. Cars where you physically turn a key in a barrel are not keyless and start on the blade.

Does my Ibiza fob take a CR2032 or CR2025? Most take a CR2032, but a few early cars use the slimmer CR2025. Check the old battery’s printed code before replacing it.

The doors won’t lock even though the engine started — why? Remote locking needs the fob’s radio, which the dead battery powers. Lock manually with the blade until you fit a fresh cell; engine starting and door locking use different parts of the key.

Will the alarm go off when I use the blade? Yes, that is normal. The mechanical override trips the alarm, and it silences as soon as the car recognises the key.

If the dash showed a fault code or warning light beside the key message, you can decode it on our sister site autodtcs.com.