Security light flashing and car won't start

Symptoms

• Security or key icon flashes on the dash
• Engine cranks but won't fire, or won't crank at all
• May work with a different key or fob
• Sometimes resolves after waiting a few minutes

Likely causes

• CommonImmobilizer doesn't recognize the key's chipA worn, damaged, or low-battery key can fail to transmit its security code properly.
• CommonWeak key fob or transponder batteryLow battery in the key can weaken the wireless signal to the immobilizer.
• PossibleInterference near the ignition (metal keychain, other fobs)Extra metal or other transponders on the ring can block the signal.
• PossibleImmobilizer control module faultA glitch or failure in the module itself can falsely reject valid keys.
• Less commonWater intrusion or corrosion in the antenna ring around the ignitionThis ring reads the key chip and can fail from moisture damage.

What to do

1. Remove all other keys and fobs from the keyring and try starting with just the one key.
2. Try your spare key if available, since a worn or damaged primary key/chip is a common cause.
3. Turn the key to 'on' and wait 5–10 minutes with it in that position, then try starting; some systems reset after a wait.
4. Replace the key fob or transponder battery if it's been more than a couple of years.
5. Check the owner's manual for a specific security light reset procedure, since these vary a lot by manufacturer.
6. If the car cranks but the security light flashes rapidly, note that pattern for a mechanic or dealer.
7. Have a dealer or qualified shop reprogram or diagnose the key/immobilizer system if basic steps don't work.
8. Avoid having extra keys cut by non-dealer sources without confirming they properly program the chip.

Tools and parts

• Spare key if available
• Owner's manual

When to call a pro

If a spare key and battery swap don't clear the security light, a dealer or automotive locksmith with the right programming tools is usually needed.

Safety