Start the Car With a Dead Key Fob Battery

Volvo V40 (2012–2019) is the P1-platform hatch, sold with a conventional ignition slot on the base car and with Keyless Drive and a START/STOP button higher up the range. Either way, a flat fob battery does not strand you: the V40 reads the key’s passive transponder up close, so you can still start the car by holding the remote to the start control with your foot on the brake.

A “Key fob battery low” message usually shows on the driver display first. Use it as your cue to fit a fresh coin cell before the remote stops responding at distance.

Starting the V40 with a dead key fob

1. Unlock and enter the car using the emergency key blade (see below).
2. Sit in the driver’s seat and press the brake pedal fully.
3. On Keyless Drive cars, hold the remote flat against the START/STOP button so the transponder sits right at the reader; on cars with an ignition slot, push the key fully into the dashboard slot instead.
4. With the brake held, press the START/STOP button (or twist the key in the slot). The car energises the transponder and the engine starts.
5. Leave the engine running until you have changed the battery, since the car may not re-detect a dead key to restart it.

Unlocking the door with the emergency key

1. Slide the release catch on the back of the remote and pull out the metal emergency key blade.
2. Go to the driver’s door. On the V40 the keyhole sits behind a cap at the rear edge of the door handle.
3. Press the blade up into the small hole on the underside of the cap to pop the cap off and expose the lock.
4. Insert the blade, turn to unlock, then refit the cap.
5. Unlocking by blade may trigger the alarm; it stops once you start the car with the key at the start control.

Immobiliser and backup-reader note

The V40 remote holds a battery-powered radio for the lock and unlock buttons and a separate passive immobiliser transponder that needs no battery. Holding the fob to the START button (or seating it in the dashboard slot) places that transponder inside the car’s antenna field, which supplies enough power to read its code. That is why a completely flat fob still starts the V40 yet can no longer lock or unlock it from a distance.

Replacing the key fob battery

The V40 remote uses a CR2032 3V lithium coin cell on most cars; some early 5-button keys take a CR2450. Check the spent cell before buying, and avoid rechargeables, whose lower 1.2V output upsets the fob.

1. Pull out the emergency key blade to release the cover.
2. Slide or unclip the cover to reach the battery seat.
3. Remove the old cell and fit the replacement of the same type, positive (+) side up.
4. Refit the cover and reinsert the blade.
5. Press a remote button next to the car to confirm it responds; the warning clears at the next start.

Frequently Asked Questions

My V40 has no dashboard slot — how do I start it? On Keyless Drive cars, hold the remote flat against the START/STOP button with the brake pressed, then press the button.

Does the V40 have a key slot? Cars with a turn key have an ignition slot; Keyless Drive cars start by button. Both read the key up close when the battery is dead.

Can the emergency key start the engine? No. The blade only unlocks the door; the remote must be at the start control to start the engine.

What battery does the V40 fob use? Usually a CR2032 3V cell; some early 5-button keys use a CR2450. Verify the old cell before replacing.

Where is the door keyhole? Behind a cap on the rear edge of the driver’s-door handle. Push the blade into the hole underneath to pop the cap off.

If a fault light or stored trouble code appears after the fob goes flat, you can decode it on autodtcs.com.