Disconnect and Reconnect the 12V Battery

Disconnecting the 12-volt battery on a Nissan Altima (L33, 2013–2018) — to replace it, or before electrical work — is straightforward, but this generation relearns several settings when power is restored. Doing it in the right order avoids a rough idle, a re-arming immobiliser and lost presets.

Before You Start

• The 12V battery is in the engine bay, front left as you face the car.
• Switch everything off, take the Intelligent Key out of the cabin and close the doors.
• The factory audio on this generation does not need a security code, but the clock and radio presets are lost.

Disconnect

1. Turn the ignition OFF, then wait about a minute so the modules power down.
2. Loosen and remove the negative (−) terminal first, and tuck the cable clear so it cannot spring back onto the post.
3. Remove the positive (+) terminal.
4. If you are removing the battery, undo the hold-down clamp and lift it out — it is heavy.

Reconnect

1. Fit the battery and connect the positive (+) terminal first; tighten it.
2. Connect the negative (−) terminal last; tighten it.
3. Do not start yet — turn the ignition ON for a few seconds so the modules wake in order, then start.

What to Relearn Afterwards

• Idle: the engine may idle rough or hunt until the ECM relearns — perform the idle air volume relearn (see that guide).
• Immobiliser: the red security light resumes its normal blink and the car recognises your key as usual — no action needed.
• Power windows: re-initialise the auto-up/down on each window — fully raise the glass and hold the switch up for about two seconds, then fully lower it and hold the switch down for about two seconds.
• Clock and radio: reset the clock and re-save your stations.
• Transmission and steering feel may take a few miles of normal driving to settle as the adaptive values rebuild.

Frequently Asked Questions

Which terminal comes off first? Negative (−) off first, and negative on last. This avoids a spanner shorting the live positive post to the bodywork.

Do I need a radio code? No — this generation’s factory head unit does not need a code. You will only lose the clock setting and saved stations.

Why is the idle rough after reconnecting? The ECM lost its idle learning when power was cut. Run the idle air volume relearn to restore a smooth idle.

Will the windows stop working properly? One-touch auto-up/down can drop out until you re-initialise each window with the raise-and-hold, lower-and-hold sequence above.

If a warning lamp stays lit after reconnecting and you want to check the code, visit our sister site autodtcs.com.