Start the Car With a Dead Key Fob Battery

Last updated: June 10, 2026

When the remote on your BMW 2 Series Coupe (G42, 2021–Present) stops working – no keyless unlock, or a key-battery warning in the cluster – the coin cell inside the fob has run flat. The G42 has no dashboard key slot, so you unlock with the hidden blade and start the engine by holding the fob against a ring antenna built into the steering column. The G42’s start sequence has one extra detail worth knowing, covered below.

Unlock the door with the emergency key blade

A dead fob cannot work the central locking, so the metal blade hidden inside it is your way in.

1. Slide the release catch at the base of the fob and withdraw the metal emergency blade.
2. At the driver’s door there is no visible keyhole – the lock barrel sits under a trim cap on the door handle.
3. Insert the blade into the recess beneath the handle and lever the cap off to expose the lock cylinder.
4. Turn the blade to unlock the driver’s door, then refit the cap once you are seated.

The alarm may sound when you unlock mechanically; it stops as soon as the car reads a valid key inside.

Start the engine by holding the fob to the steering column

The G42 has a ring aerial in the steering-column surround that energises the fob’s chip and reads its code.

1. Sit in the driver’s seat, close the door, and press the brake pedal.
2. Find the small key symbol on the steering-column trim, usually on the right-hand side.
3. Hold the flat back of the fob completely flush against the symbol, making firm contact with the plastic.
4. Press and hold the Start/Stop button until the “no key” warning clears from the display.
5. Release the button, then press it again with the brake down to start the engine.

If it does not catch, reposition the fob a few millimetres against the symbol – the chip’s coil has to align with the aerial behind it.

Why a flat fob still authorises the engine

Only the remote-control side of the fob – locking, boot, Comfort Access – draws on the coin cell. Engine authorisation comes from a passive transponder chip that carries no battery; the column ring aerial induces a current in its coil, powering the chip just long enough to read the security code and release the immobiliser. The blade is mechanical only, so it opens the door but never starts the car.

Replace the fob battery (CR2032)

With the car running again, fit a fresh cell to restore keyless operation.

1. Pull out the emergency blade; the gap it leaves is the opening point for the case.
2. Ease the two halves of the housing apart along the seam until the back cover comes free.
3. Lift out the spent CR2032 coin cell, noting its orientation, and press the new one in to match.
4. Close the case, refit the blade, and lock/unlock the car to confirm the remote is alive.

If a key warning lingers after a new cell, clean the contacts with a dry cotton bud before refitting.

Frequently Asked Questions

Why does the G42 need the button held until the warning clears? Holding Start/Stop gives the ring aerial time to power the dead chip and read its code. Once the “no key” message disappears the car has authorised the key, and a second press starts the engine.

Does the G42 have a key slot? No. It uses only the steering-column ring aerial, so hold the fob against the key symbol rather than looking for a slot.

The alarm sounded when I used the blade – is that a fault? No. Mechanical unlocking bypasses the remote, so the alarm arms briefly and silences once the immobiliser reads your key.

Fob held to the column and still no start – what now? Reposition the fob and retry. If the car is dead or only clicks, the cause is more likely the G42’s 12 V battery than the fob.

What battery does the G42 fob use? A single CR2032 3 V lithium coin cell. Handle it by the edges when fitting.

If a warning light stayed on after the key trouble, you can decode it on our sister site autodtcs.com.