Symptoms
- Key goes into the ignition (EZS) but the dash stays dark: no ignition
- Sometimes the key won't turn in the ignition switch at all
- Both keys stop working at the same time. If you only have one key, it's easy to blame the key
- Remote central locking on the key still works perfectly
- No usual whirr or click from the steering column when the key goes in
- Often starts as an intermittent 'try it again' fault before failing completely
Why it happens
On these FBS3-era Mercedes, the electronic steering lock (ESL, called ELV by Mercedes) is part of the immobiliser routine. When you insert the key, the ignition switch (EZS) checks the key, then asks the steering lock to unlock and confirm its position. If the steering lock doesn't report back in the expected position, the EZS refuses to switch the ignition on, and the car won't start.
Wear in the lock's motor and electronics is the usual cause. Most fail in the unlocked position, so the steering still turns but the car won't start. Because the key and remote are fine, people with two keys are surprised when both fail at once, and people with one key usually assume the key is at fault.
How it's diagnosed
Fault codes for this failure vary and aren't always stored. We confirm it properly with a diagnostic tool, by checking the live data from the ignition switch (EZS), the steering lock (ESL/ELV) and the key. If the steering lock isn't reporting "unlocked" while the key is recognised, the steering lock is the culprit, not the key.
Models affected
| Model | Years | Code |
|---|---|---|
| Mercedes C-Class (pre-facelift) | 2007-2011 | W204 / S204 |
| Mercedes C-Class (facelift) | 2011-2014 | W204 / S204 |
| Mercedes E-Class (pre-facelift) | 2009-2013 | W212 / S212 |
| Mercedes E-Class Coupé / Cabriolet (pre-facelift) | 2009-2013 | C207 / A207 |
All on the FBS3 immobiliser platform. The facelift W212 (2013 on) moved to FBS4 and isn't covered by this repair.
How we fix it
- Confirm it's the steering lock. We check the key, the ignition switch (EZS) and the steering lock data so you don't pay for the wrong fix.
- Fit an ESL emulator. The failed steering lock is replaced electronically by an emulator that answers the EZS exactly as a healthy lock would.
- Program it to the car. The emulator is programmed and matched to your car's immobiliser.
- Test. Ignition, start and both keys checked before we leave.
This is a mobile-only repair. We come to the car, which is handy because it won't be going anywhere until it's fixed.
Before you call: quick checks
- Try your spare key. If both fail and the remotes still lock the car, it points to the steering lock, not the keys.
- Gently wiggle the steering wheel while turning the key, just in case it's simply bound up. Don't force it.
- Check the battery is healthy. A very flat battery can mimic this fault.
- Is the steering stuck in the locked position? Call before booking.
Price & time
£245, fitted and programmed on site. Mobile only. No fix, no fee.
Questions
Why is my Mercedes key not working but the remote still locks the car?
On W204 and W212 models the remote and the immobiliser are separate. If the electronic steering lock (ESL/ELV) fails, the ignition switch won't switch on even though the key is fine, which is why the remote still works.
Do I need a new key or ignition switch?
Usually neither. If both keys fail at once and the remote still works, the steering lock is the usual cause. We confirm it before doing anything.
Is the facelift E-Class affected?
This repair covers the FBS3 cars: W204 C-Class (pre-facelift and facelift) and pre-facelift W212/C207 E-Class. The facelift W212 uses a different system.
Can I bring the car to you?
It won't start, so we come to you. This repair is mobile only.