Start the Car With a Dead Key Fob Battery

Last updated: June 10, 2026

If the remote on your Ford Puma (2020–present) has gone dead and the doors will not open or the dash flashes “Key not detected”, you are not stranded. The Puma is keyless throughout the range, so there is no twist barrel to fall back on — but it still hides a metal emergency blade to get you in and a backup way to start the engine on a flat fob battery.

This applies to the whole Puma line including the mild-hybrid EcoBoost and the ST. Because every Puma uses the KeyFree START/STOP button, the contact-start method below is the one almost every owner will need when the coin cell finally runs out.

Start the Puma With a Dead Fob

With a flat fob the Puma’s immobiliser can still read the key at very close range using the backup transponder coil built into the START/STOP button. Do this:

1. Get into the car first using the emergency blade (see the next section) — the door buttons are dead on a flat fob.
2. Sit in, press the brake pedal and hold it down.
3. Hold the flat face of the key fob directly against the START/STOP button so the transponder coil sits right on the reader behind it.
4. Press the button through the fob. The immobiliser powers the passive chip, recognises your key and releases the engine.
5. The engine starts. If nothing happens first time, rotate the fob a few degrees and press again — the read zone behind the button is small.

The Puma has no drop-in cubby slot, so touching the fob to the button is the official backup. A “Key not detected” message is your cue to use it.

Unlock the Puma With the Emergency Key Blade

A metal blade is folded inside the fob for getting through the door.

1. Slide the release catch on the back of the fob and pull the metal emergency blade straight out.
2. Go to the driver’s door. The lock cylinder hides behind a small plastic cap on the door handle. Slip the blade into the slot at the rear edge of the cap and prise the cover off to expose the barrel.
3. Insert the blade and turn it to unlock the door — this usually opens the driver’s door only; the interior central-locking button frees the rest once you are in.

A Word on the Puma’s Deadlock

The Puma is known for a specific catch: when the fob battery dies and the car was deadlocked (double-locked) on parking, you may hear the lock turn with the blade but the door still will not open, because the deadlock is still engaged. If that happens, turn the blade fully and firmly — the driver’s door is the designated override and a complete turn should release both the lock and the deadlock. If a door has frozen or the mechanism is stiff, the driver’s door is still your best bet; the rear doors are not set up as emergency entry points.

Why a Flat Battery Does Not Lock You Out

The Puma’s immobiliser never relied on the coin cell to verify your key. Inside the fob is a passive transponder powered by induction from the car’s reader coil, like a contactless card. The dead battery only kills the long-range radio that unlocks the car from a distance. Hold the fob to the button and the short-range coil powers the chip directly, so the car still recognises it as your key.

Replace the Key Fob Battery

1. Slide out and remove the emergency blade first — this releases the case.
2. Split the fob along its seam with a thin coin or plastic pry tool.
3. Lift out the old cell. The Puma fob uses a single CR2032 3V coin cell.
4. Fit the new battery + side facing the same way as the old one, handling it by the edges.
5. Clip the case together, refit the blade and test the buttons. Expect 2–3 years from a fresh cell.

Frequently Asked Questions

Where do I hold the fob to start the Puma? Flat against the START/STOP button on the dash. That is where the backup reader coil sits — the Puma has no drop-in slot.

The blade turned but the door still won’t open — why? The Puma was likely deadlocked. Turn the blade fully and firmly in the driver’s door; a complete turn releases the deadlock as well as the latch.

Where is the hidden door lock on the Puma? Behind a clip-off plastic cap on the driver’s door handle. Prise the cap from its rear edge to reveal the barrel.

Which battery does the Puma fob take? A CR2032, a common 3V coin cell sold everywhere.

The car only started when I held the fob to the button — is something wrong? Usually just a weak or flat fob battery. Fit a fresh CR2032; if it keeps happening, the fob transmitter may be failing.

If a warning light stayed on after all this, you can look up what the code means on our sister site autodtcs.com.