Disconnect and Reconnect the Battery

Last updated: June 5, 2026

Disconnecting the 12 V battery on a Toyota Aygo Mk2 (B40, 2014–2021) is a straightforward job for a battery change or before electrical work. There is no dealer registration to worry about, but the stop & start system needs a quick relearn afterwards and you should note your radio settings first. This guide covers the safe order of work.

Where the Battery Is

The battery is in the engine bay. Lift any cover to reach the two terminal clamps. Fit a like-for-like replacement if you are renewing it — cars with Stop & Start use an enhanced battery, so match the original specification.

Before You Disconnect

• Note your radio stations and personal settings (and any audio security code, if used).
• Turn the ignition off and remove the key (or keep the keyless fob away from the car).
• After switching off, wait 90 seconds before disconnecting — this lets the modules power down cleanly.
• If working near airbags or seat-belt pretensioners, allow the system to discharge before handling those parts.

Disconnecting — Correct Order

1. Turn the ignition off and wait 90 seconds.
2. Slacken the negative (−, earth) terminal first and lift the lead clear.
3. Only undo the positive (+) terminal if you are removing the battery completely.
4. If removing the battery, undo the hold-down clamp and lift it out upright.

Reconnecting — Correct Order

1. Refit the battery and secure the hold-down clamp.
2. Connect the positive (+) lead first, then the negative (−) earth lead last. Tighten both firmly.
3. Turn the ignition on for a few seconds before starting the engine.

Re-initialise the Stop & Start System

If your Aygo has Stop & Start, the system stays dormant after a battery disconnection until it relearns the battery’s state. Simply start the engine and drive normally — after the engine reaches temperature and the battery has charged, Stop & Start re-arms on its own (usually within a trip or two). No button press is needed.

What Else to Reset

• Reset the date and time and re-enter your radio code, presets and preferences.
• Re-initialise the tyre-pressure system once your pressures are correct — the Aygo’s reset button is in the glovebox (see our Aygo TPMS reset guide).

If a Warning Light Stays On

One or two lights right after reconnecting is normal and should clear on a short drive. If the airbag, ABS or engine light stays on, a fault code was logged — reading it needs an OBD scanner, and you can look up what a Toyota code means on our sister site autodtcs.com.

Frequently Asked Questions

Do I need to register a new battery on an Aygo?

No — Toyota does not require battery coding on this model. Fit the correct battery, reconnect, and restore your settings.

Why won’t Stop & Start work after the battery change?

It stays dormant until the battery is fully charged and the system has relearned. Drive normally and it returns — usually within a trip or two.

How long should I leave it disconnected to reset the electronics?

Around 10–15 minutes with the doors shut lets the modules power down fully.

Will I lose my radio?

Some Aygo head units ask for a security code after a power loss. Have it ready, or use a memory-saver to avoid it.

To clear the service reminder after maintenance, see our Toyota Aygo service indicator reset guide.