These instructions apply to the Volvo S40 Mk2 (544) 2004-2012.
For other models, please choose your vehicle here.
Disconnecting the 12 V battery on the Volvo S40 — to change it or work safely on the electrics — is straightforward, but the airbags and the memory settings need the right order. Here is the safe sequence to take it off and put it back.
Disconnect and reconnect the S40 battery
- Make sure the ignition key is fully OFF and the car is locked-down (lights and radio off) before you touch the battery cable.
- Loosen and remove the negative (−) terminal first, then the positive (+).
- If you are working near airbags or seat-belt pre-tensioners, wait three minutes after disconnecting for the system to fully power down.
- To refit, connect the positive (+) terminal first, then the negative (−), and tighten both.
- When you first switch the ignition on, reach in from outside the car and keep clear of the airbag areas as a precaution.
- Drive the car, then re-initialise the door mirror and driver’s seat positions if they moved.
If you jump-start or charge the battery, always use a solid chassis earth point as the ground, not the bare negative terminal.
Frequently asked questions
Will I lose any settings?
The clock, radio presets and some memory functions reset. The engine also relearns its idle over the first few miles, so a slightly uneven idle straight after reconnection is normal.
Which terminal comes off first?
Always the negative first when removing, and the negative last when refitting — that avoids a short if your spanner touches bodywork.
Where is the battery on the S40?
Under the bonnet in the engine bay on most petrol cars. Some models carry it under the boot floor; check both if it is not where you expect.
If a warning light stays on after reconnecting, look up the code on autodtcs.com.
Independent guide — not affiliated with Volvo. Always follow your official service manual and safety precautions. Read our full disclaimer.