Start the Car With a Dead Key Fob Battery

Last updated: June 10, 2026

The Toyota Yaris Cross (2021–Present) is the GA-B-platform compact crossover sold mostly as a hybrid, with Smart Entry and push-button start standard on mid and upper grades. When the key fob coin cell dies, the keyless link drops and the dash flags a key warning — but you can still get in and away using the backup Toyota builds into the fob. Here is the Yaris Cross procedure step by step.

Start the Yaris Cross With a Dead Fob

The car can read the chip inside the fob at very close range even when the battery is flat, so you bring the fob to the button.

1. Unlock and get in (mechanical-key steps below), then sit in the driver’s seat with the door closed.
2. Press the brake pedal fully and hold it.
3. Touch the fob flat against the START/STOP button, the Toyota-badge face to the button. Wait for the beep that confirms detection.
4. With the brake still down, press START. The hybrid powers up to READY.

As a hybrid there may be no engine crank — the green READY light and a fully-lit display tell you it has started. No beep? Turn the fob over and try the other face squarely against the button.

Unlock With the Hidden Mechanical Key

A dead fob won’t operate the door buttons, so use the emergency blade inside it.

1. Press the release on the fob and slide the metal key out.
2. At the driver’s door, the lock cylinder sits behind a small cover on the handle. Lever the cover off with the blade tip to reveal the keyhole.
3. Insert and turn to unlock. The alarm may chirp; starting the car clears it.

Why the Touch-to-Button Trick Works

Behind the start button is a short-range induction antenna that powers and reads the passive transponder in the key — a chip with no battery of its own. Only the longer-range radio for hands-free unlocking depends on the coin cell, so a dead battery leaves the close-range immobiliser handshake working. That is the designed-in limp-home path for every Toyota Smart Key car.

Replace the Coin Cell

Change the battery the same day so hands-free entry returns.

1. Slide out the mechanical key to expose the case seam.
2. Twist a coin in the slot to split the fob halves.
3. Check the old cell before buying: many Yaris-family fobs take a CR2032, but some Yaris and Yaris Cross fobs use the slightly thinner CR2025 — both are 3V lithium, and the writing on the old battery confirms which. Fit the new one positive (+) side the same way up.
4. Handle the cell by its edge and click the case shut.

Stand by the car and press lock once; the buttons should respond again.

Frequently Asked Questions

Is my Yaris Cross fob a CR2032 or CR2025? It varies by fob version. Open the fob and read the number printed on the old coin cell — that is the only reliable way. Don’t force a thicker CR2032 into a holder designed for a CR2025.

How do I know the hybrid has actually started? The green READY light comes on and the instruments fully illuminate. The petrol engine may stay silent at first — that is normal for a hybrid.

Where is the door keyhole? Hidden under a small cap at the rear of the driver’s door handle; the passenger doors have no barrel.

A key warning stayed on after a new battery. The same message can come from a weak 12V battery. If a fresh coin cell doesn’t restore keyless entry, have the 12V tested.

Can the metal key start the car? No — it only unlocks the driver’s door. Starting is always via the push button.

If a warning light lingered after you drove off, our sister site autodtcs.com can decode the stored fault so you know whether it relates to the smart-key system.