Disconnect and Reconnect the Battery

Disconnecting the 12 volt battery on a fourth-generation Subaru Legacy (BL sedan / BP wagon, 2003–2009) is straightforward, but a few preparations save you from a locked radio and dropped settings afterwards. The battery sits in the engine bay.

How to disconnect and reconnect the battery

Work with the engine off and every electrical consumer switched off. Note your audio security code before you start, because the head unit can lock when power is removed.

1. Turn the engine off and switch off the lights, climate fan, audio and any other consumers.
2. Write down the radio security code and make a note of your preset stations and settings.
3. Open the hood and locate the battery in the engine compartment.
4. Loosen the clamp and disconnect the negative (−) terminal first, then the positive (+) terminal.
5. If you are working near pyrotechnic parts such as airbags or seat-belt pretensioners, wait at least one minute after disconnecting before touching them.
6. To reconnect, fit the positive (+) terminal first, then the negative (−), and tighten both clamps securely.
7. Reset the date and time, re-enter the radio code, and restore your preset stations and preferences.
8. Initialize the power windows so the one-touch and auto-up function works again.

Always remove the negative terminal first and refit it last. This keeps a spanner from shorting against the body while the positive side is still live.

Why settings are lost

With the battery removed, the car loses keep-alive power. The clock, radio presets, and the power-window control module all forget their stored values, so each needs a quick re-set once power is back.

Frequently asked questions

Which terminal do I remove first on a Subaru Legacy?
Always the negative terminal first, then the positive. On reconnection, reverse it: positive first, negative last.

Will disconnecting the battery clear fault codes?
It can clear stored trouble codes and freeze-frame data. If a warning light was on, the underlying fault may still be present and the light can return.

Do I need to relearn anything after reconnecting?
Yes — set the clock, re-enter the radio code, restore radio presets, and initialize the power windows.

If a dashboard warning light stays on after you reconnect the battery, read the stored fault code first. You can look up what each code means on autodtcs.com.