🔑 Key Fob Battery Replacement

Symptoms of a Weak Key Fob Battery

• "Smart key battery low" warning on the Multi-Function Display (MFD)
• Reduced range — you have to be right next to the car for it to detect the key
• Door doesn't unlock when you approach or touch the handle
• The POWER button doesn't respond normally even when you're inside with the fob
• Intermittent detection — sometimes works, sometimes doesn't

What Battery You Need

CR2032 — a 3V lithium coin cell. This is one of the most common coin batteries made. Available at any pharmacy (Walgreens, CVS), hardware store, grocery store, AutoZone, Walmart, or online. Costs $3–5 for a single, or less if bought in a multi-pack. Any brand works — Panasonic, Energizer, Duracell, and generic all perform similarly in this application.

How to Open the Key Fob

The Gen 2 Prius uses a Smart Key fob — a black rectangular remote with a hidden mechanical emergency key inside. Opening it takes about 30 seconds once you know the method.

1. Release the mechanical key. On the back of the fob, there's a small sliding tab or button (usually on one of the short ends). Press or slide it and pull out the thin metal key that's tucked inside. Set the key aside — you don't need it for this but you will need it later.
2. Find the seam where the key was. With the metal key removed, there's now a slot at the end of the fob where the key came out. This is your pry point.
3. Insert a coin or small flathead screwdriver into that slot and gently twist to separate the two halves of the case. Work slowly — the plastic tabs are small but not fragile if you're not forcing it. Don't use a sharp metal tool along the outer seam; you'll scratch the case and risk cracking a clip.
4. The two halves will separate. Inside you'll see the circuit board and the CR2032 battery in a holder. Note which side of the battery faces up (the "+" side is marked on the battery and typically faces up).
5. Pop out the old battery using a fingernail or the corner of a flathead. Slide in the new CR2032 with the same orientation — positive side up.
6. Snap the two halves back together — press firmly along the seam until all the clips click. Reinsert the mechanical key until it locks in place.
7. Test it — walk away from the car and press Lock or Unlock. If the car responds, you're done.

Emergency Start — If the Battery Is Completely Dead

If the fob battery dies while you're out and you don't have a spare, the Prius can still be started. Toyota built this in specifically for this situation.

1. Get inside the car. If the door handle doesn't work (no battery to transmit), use the mechanical key hidden inside the fob to unlock the driver's door manually. The keyhole is behind a small cover on the door handle.
2. Find the key fob slot on the dashboard. The Gen 2 Prius has a dedicated slot for this — it's on the lower-left area of the instrument panel, to the left of the steering column. It's sized to accept the full fob.
3. Insert the key fob fully into the slot. The slot's antenna reads the fob's passive transponder at close range — no battery needed for this.
4. Press the POWER button with your foot on the brake as you normally would. The car should start normally.

Notes from the Field