Start the Car With a Dead Key Fob Battery

Last updated: June 10, 2026

The Audi A3 (8V, 2012–2020) was sold both as a turn-key car and, with the Advanced Key option, as a keyless push-button car. When the fob’s coin cell goes flat the remote buttons stop responding, but the immobiliser still reads the transponder — on keyless 8Vs by holding the fob against the steering column, on turn-key cars simply via the blade in the ignition.

Start a keyless A3 8V with a dead fob

If your A3 has Advanced Key and a START ENGINE STOP button:

1. Enter the car with the emergency blade first (next section), sit in the driver’s seat and close the door.
2. Press and hold the brake pedal.
3. On the steering column, look for the key symbol on the trim cover — this is the back-up reader location for the 8V.
4. Hold the flat face of the fob against that symbol and keep it there.
5. Press the START ENGINE STOP button while pressing the fob in place; the engine starts.

Turn-key A3 8V — the blade starts it

On a standard A3 8V with an ignition barrel, a dead fob disables only the remote-lock buttons. Pull the blade, unlock the driver’s door, then insert the blade in the barrel and start the car as normal — the transponder in the key head is read directly.

Unlock the A3 8V with the emergency key blade

1. Press the release on the fob and slide the metal blade out of the body.
2. At the driver’s door, the lock barrel hides under a small cap on the handle. Insert the blade into the slot at the base of the cap and lever it off.
3. Insert the blade into the barrel and turn to unlock. The alarm may chirp until you start the engine.

Why a flat fob still starts the A3

The 8V fob’s coin cell powers the remote buttons and, on Advanced Key cars, the proximity broadcast. The chip that authorises the engine is a passive RFID transponder energised by the car — the ignition barrel on turn-key cars, the column coil on keyless cars. Because it never relies on the cell, the immobiliser can verify the key even when the fob is completely dead.

Replace the fob battery

The A3 8V fob uses one CR2032 3V lithium coin cell. On the slim Advanced Key smart fob, slide out the blade and squeeze the release clips inside the key slot to draw the battery tray out — do not prise the casing. On the standard flip key, open the case at the seam. Fit the new cell + side up and reassemble; remote functions return at once.

Frequently Asked Questions

Does my A3 8V have keyless start?

Only if it was ordered with Advanced Key. Those cars have a START ENGINE STOP button; standard cars use a turn-key barrel and just need the blade.

Where is the back-up reader on a keyless 8V?

On the steering column trim, marked with a key symbol. Hold the fob flat against it before pressing the start button.

How do I open the smart-key fob without breaking it?

Don’t prise the casing on the slim Advanced Key fob. Pull the blade, then squeeze the clips inside the key slot to slide the battery tray straight out.

The remote stopped working but the car still starts — normal?

On a turn-key 8V, yes — the flat cell kills only remote locking while the key’s transponder still starts the engine. Replace the CR2032 at your convenience.

Why did the alarm sound when I used the blade?

Mechanical entry looks like a break-in until the transponder is verified. Starting the engine cancels the alarm.

If a warning light stayed on after the no-start, look it up on autodtcs.com to confirm it was just the fob and not an immobiliser code.