Car won't start - key not recognized

Symptoms

• Dash shows a 'key not detected' or similar message
• Engine won't crank or crank is blocked electronically
• May work with a spare key
• Fob or key may have been recently dropped, wet, or exposed to extreme temperatures

Likely causes

• CommonWeak or dead key/fob batteryThis is the most common and simplest cause of a key not being recognized.
• CommonPhysically damaged key or transponder chipDropping, bending, or heavy wear can damage the internal chip.
• PossibleInterference from other keys, fobs, or metal objects nearbyExtra items on a keyring can block proper signal reading.
• PossibleImmobilizer antenna ring or module faultThe receiver that reads the chip can fail or corrode over time.
• Less commonKey not properly programmed to the vehicle (recently replaced key)A newly cut key that wasn't fully programmed will not be recognized.

What to do

1. Replace the battery in the key or fob first, since this resolves the majority of 'key not recognized' cases.
2. Remove all other keys, fobs, and metal objects from the keyring and try again with just the one key.
3. Try your spare key to determine whether the problem is the key itself or the car's system.
4. If you recently had a new key cut, confirm with the locksmith or dealer that it was fully programmed, not just cut to shape.
5. Check for visible damage to the key, like cracks or exposure to water, that might affect the internal chip.
6. Try holding the key very close to the ignition switch or the backup start location specified in your owner's manual.
7. If none of this works, have a dealer or automotive locksmith test the key and the vehicle's immobilizer antenna.
8. Keep a properly programmed spare key on hand for situations like this in the future.

Tools and parts

• Spare key if available
• Replacement fob/key battery

When to call a pro

If a battery swap and spare key don't resolve a 'key not recognized' message, a dealer or locksmith can test and reprogram the key or check the antenna ring.

Safety