Start the Car With a Dead Key Fob Battery

Last updated: June 10, 2026

The Toyota Aygo (Mk2/AB40, 2014–2021) — the city car developed alongside the Peugeot 108 and Citroën C1 — is different from most Toyotas here: the vast majority of Mk2 Aygos use a conventional bladed turn-key ignition, not push-button start. Smart Entry with a START/STOP button was reserved for the top x-clusiv trim. That means for most owners a flat fob battery is barely an inconvenience. Here is what to do for each version.

Turn-Key Aygo: A Dead Fob Barely Matters

If your Aygo has an ignition barrel on the steering column and a flip-out blade in the remote, the coin cell only powers the lock/unlock buttons on the fob. With a dead battery:

1. Use the blade to unlock the driver’s door manually at the door lock (steps below).
2. Get in, insert the same blade into the ignition barrel and turn as you always do.
3. The engine starts normally — the immobiliser reads the chip in the key, which needs no battery.

In other words, the dead fob battery costs you only the remote central locking; the car drives exactly as before. Replace the coin cell at your convenience to get remote locking back.

x-clusiv (Smart Entry) Aygo: Touch the Fob to the Button

If your Aygo has Keyless Smart Entry and a START/STOP button, a dead fob is handled the Toyota way — bring the fob to the button so the car can read its chip up close.

1. Unlock and get in (mechanical-key steps below), then sit in the driver’s seat with the door shut.
2. Press the brake pedal fully and hold it.
3. Touch the fob flat against the START/STOP button, badge face to the button, until you hear a beep.
4. With the brake still down, press START. The Aygo fires up.

No beep? Flip the fob and try the other face square against the button.

Unlock With the Mechanical Key

Either version uses the metal blade to open the driver’s door when the remote is dead.

1. On a flip-key, fold the blade out; on a Smart Key, press the catch and slide the blade out.
2. The driver’s door has a keyhole in or just behind the handle — on the Aygo it is usually visible, not capped.
3. Insert and turn to unlock. If the alarm sounds, turning the ignition on (or starting the car) clears it.

Why the Chip Still Works

Every Aygo key carries a passive immobiliser transponder. On the turn-key car the barrel’s antenna reads it; on the Smart Entry car the antenna behind the START button reads it. Either way the chip is powered by the antenna’s field, not the coin cell — so a flat battery never stops the engine starting, only the remote radio for locking and (on x-clusiv) hands-free detection.

Replace the CR2032 Coin Cell

The Aygo Mk2 remote runs on a single coin cell.

1. Remove or fold out the blade to expose the case seam.
2. Twist a coin or small flat screwdriver in the slot to part the two halves.
3. Lift out the old battery. The Aygo Mk2 fob uses a CR2032 3V lithium coin cell. Fit the new one positive (+) side the same way the old one sat.
4. Handle the cell by its edge, then click the case shut.

Stand by the car and press lock once; remote locking should be back.

Frequently Asked Questions

How do I know if my Aygo is turn-key or Smart Entry? Look at the column: a key barrel means turn-key (the common case); a START/STOP button means x-clusiv Smart Entry. The key itself differs too — a flip blade versus a chunky smart fob.

My turn-key Aygo won’t start even though the fob is dead — why? A dead fob can’t stop a turn-key Aygo from starting. If it cranks but won’t fire, or won’t crank, suspect the 12V battery or immobiliser, not the fob coin cell.

Is the Aygo’s door keyhole hidden? Usually no — unlike larger Toyotas, the Aygo Mk2 generally has a visible barrel on the driver’s door handle.

Can I start the x-clusiv with just the blade? No — on the Smart Entry car the blade only unlocks the door; starting is via the button using the touch method.

Does the Aygo share its key with the Peugeot 108 / Citroën C1? The cars are mechanically related, but use the Toyota fob and the procedures above; don’t assume a 108/C1 remote will pair to your Aygo.

If a warning light stayed on after you got going, you can decode the exact fault on our sister site autodtcs.com to see whether it relates to the immobiliser or something else.