Start the Car With a Dead Key Fob Battery

Last updated: June 10, 2026

The Toyota RAV4 (Mk4/XA40, 2013–2018) was offered both with Smart Entry & push-button start on higher grades and with a conventional bladed turn-key on entry models. Which fix you need depends on that split — but on a push-button XA40, a dead fob is easy to work around once you know to bring the fob to the button. Here is the full procedure.

Push-Button RAV4: Start It With a Dead Fob

On a Smart Entry XA40 the fob normally authorises the car by radio. A flat coin cell drops that link — the dash shows “Key not detected” — but the car can still read the chip inside the fob up close.

1. Get in first (mechanical-key steps below) and sit in the driver’s seat with the door closed.
2. Press the brake pedal fully and hold it.
3. Hold the fob flat against the START/STOP button, badge face to the button, until the indicator light turns green (a beep often accompanies it).
4. With the brake still down, press START. The RAV4 cranks and starts.

If nothing happens, reposition the fob so its face sits squarely over the button, or flip it and try the other side — the read coil behind the button has only a centimetre or two of reach.

Unlock With the Hidden Mechanical Key

A dead fob won’t open the doors by radio, so use the blade hidden inside the Smart Key.

1. Slide the catch on the fob and pull the mechanical key out.
2. At the driver’s door, the lock cylinder sits behind a cap on the handle. Lever the cap off with the blade tip to reveal the keyhole.
3. Insert and turn to unlock. The alarm may sound until you start the car.

Entry-grade XA40s with the bladed turn-key are simpler: the same key unlocks the door and turns the ignition, so a flat fob battery only disables the remote-lock buttons — the car starts as it always does.

Why Touching the Fob to the Button Works

An induction antenna behind the start button powers and reads the passive transponder built into the key — a chip with no battery, woken by the antenna’s field. The dead coin cell only kills the longer-range radio for hands-free unlocking; the close-range immobiliser handshake still completes. That is the official limp-home method Toyota builds into every Smart Key RAV4.

Replace the CR2032 Coin Cell

The XA40 smart key lasts roughly two to three years on a coin cell.

1. Pull the mechanical key out to expose the case seam.
2. Twist a coin or small flat screwdriver in the slot to part the two halves.
3. Lift out the old battery. The RAV4 Mk4 fob uses a CR2032 3V lithium coin cell. Fit the new one with the positive (+) side the same way the old one sat.
4. Handle the cell by its rim, then click the case shut.

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

Frequently Asked Questions

How do I tell if my XA40 has Smart Entry or a plain key? If your key is a chunky fob with a START/STOP button on the dash, it’s Smart Entry — use the touch-to-button method. If you have a turn-key in a barrel on the steering column, the dead fob only affects remote locking.

The light turns green but it still won’t start. Press the brake fully and push START promptly after the green light. If there’s no green light at all, try the other face of the fob hard against the button.

Where is the door keyhole? Behind a removable cap at the rear of the driver’s door handle; only that door has a barrel.

Could a weak 12V battery cause the warning? Yes — if a fresh coin cell doesn’t fix keyless entry, or the engine cranks slowly, test the main 12V battery.

Can the metal key start a push-button RAV4? No — the blade only unlocks the door. Starting is always through the button.

If a warning light stayed lit after you drove off, you can decode the exact fault on our sister site autodtcs.com to see whether it relates to the smart-key system.