The Surprising Connection Between Fob Battery and Engine Start
On vehicles with keyless entry and push-to-start ignition (also called smart key, proximity key, or hands-free key systems), the car must detect the key fob in the cabin before allowing the start button to work. If the fob battery is very flat, the car may not detect it — and the engine simply won't start when you press the button.
This catches many NZ drivers off guard. The car worked fine yesterday, nothing seems wrong, but pressing the start button does nothing.
How to Start a Push-to-Start Car With a Dead Fob Battery
Almost all push-to-start vehicles have a backup procedure for exactly this situation. The most common method:
Hold the fob directly against the start button. The button itself often has an inductive pickup coil that can read the key's transponder chip even without the fob's battery. Hold the fob flat against the start button (or the base of the column, depending on the vehicle) and press. Consult your owner's manual for the exact location.
Use the hidden mechanical key. Most smart key fobs contain a small metal key blade — slide the back off the fob to access it. This can open the driver's door manually (there's usually a keyhole hidden under a trim cap) and can also be used to trigger the fob reader in some vehicles.
Replacing the Fob Battery
Smart key fobs use a flat coin-cell battery, typically a CR2032 (less commonly CR2025 or CR2450). These cost $3–$8 NZD from supermarkets, service stations, and electronics stores.
To replace:
- Locate the notch or slide on the fob's casing and separate the two halves (some require a small coin or screwdriver).
- Note the battery orientation (+ side up or down) before removing the old one.
- Fit the new battery and reassemble.
- Test from close range — the range should return to full within a few presses.
A fob battery typically lasts 2–4 years depending on how often you use keyless functions and how close you park to the car (some passive keyless systems are active all the time, draining the battery faster).
When a New Battery Doesn't Fix It
If you've replaced the battery and the fob still doesn't work reliably:
- The fob itself may have a fault — internal solder joints can crack
- The fob may need re-pairing to the car (can lose pairing after deep battery discharge on some vehicles)
- The car's key antenna or receiver may have developed a fault
Fob replacement or re-pairing at a dealer typically costs $80–$300 NZD depending on the vehicle.
Preventing the Problem
- Replace fob batteries proactively every 2–3 years rather than waiting for failure
- Keep a spare fob battery in the glovebox
- Note when the car starts showing a "low key battery" warning on the dash — act on it