Mercedes key won't turn? It's often not the key.

Check first

1. Try the spare key.
2. Replace the key battery.
3. Wiggle the steering wheel gently while turning.

If the spare works, it's the key. If neither works, it's the car.

Steering lock

Many W204 and W212 cars use an electronic steering lock. When it fails, the EIS refuses to turn the key.

EIS

The EIS reads the key by infrared and checks the secret data. Worn or failing units stop recognizing keys.

What we do

We diagnose at the car and explain what we found before anything is replaced. If the fix is a new key, we make it on FBS3 cars.

Written by Key Monkey, European car key specialist in Marietta, GA. Updated October 23, 2026.