Immobilizer light flashing and car won't start

Symptoms

• Small key or lock-shaped icon flashes on the dash
• Engine cranks but won't fire, or won't crank at all
• Car may start with a spare key but not the usual one
• Warning may say 'security' or 'immobilizer'

Likely causes

• CommonWeak key fob batteryThe chip inside the key needs enough power from the battery to communicate with the car's immobilizer system.
• PossibleFob not close enough to the readerSome cars need the key very close to a specific spot, like the steering column, to read the chip.
• PossibleDamaged or failing chip in the keyPhysical damage, extreme heat, or age can degrade the transponder chip inside the key.
• Less commonImmobilizer module or antenna ring faultA failure in the car's own reader can prevent it from recognizing any key.

What to do

1. Replace the key fob battery, then try starting again.
2. Hold the key very close to the ignition switch or start button, since the reader has limited range.
3. Try any spare key you have to see if the problem follows a specific key or is present with all keys.
4. If a spare key starts the car fine, the original key or its chip is likely the problem.
5. If no key works, the issue is more likely the car's immobilizer system rather than the keys themselves.
6. Avoid repeated cranking attempts, which can drain the battery further without success.

Tools and parts

• Replacement coin-cell battery

When to call a pro

If no key starts the car, or a spare key also fails, have a dealer or locksmith diagnose the immobilizer system.

Safety