// What fails
The Mercedes EZS (Elektronisches Zündschloss, also called EIS) is the electronic ignition switch that reads your key, releases the steering lock and wakes the car up. Inside it, processor and power-supply components fail with age, contacts wear, and voltage spikes from tired batteries kill the electronics — leaving a key that will not turn, or a key that is simply ignored.
Because the EZS is married to your keys and the immobiliser, a used replacement is not a simple swap. We repair the original unit at component level, keeping your existing keys working — a job we have been doing since the days of the W209 and W639 Vito write-ups in our blog.
Symptoms we see every week
- Key goes in but will not turn in the ignition
- Key not recognised — no dash lights when inserted
- Intermittent starting: works one day, dead the next
- Remote central locking stopped responding
- No communication with the EZS on diagnostics
Our process
- DiagnoseThe fault is confirmed with proper diagnostics and board inspection before any work is quoted.
- RepairComponent-level repair on your original unit — coding, keys and adaptations preserved.
- Bench testThe repaired unit is proven on the bench under realistic conditions before it goes back.
- WarrantyWork is covered by our workshop warranty, with terms confirmed in writing on your quote.
We test your keys against the repaired EZS on the bench before anything goes back in the car, so you know the whole chain — key, ignition, immobiliser — works as one.
Pricing
EZS/EIS pricing depends on the chassis and fault, so we quote per job. Call or WhatsApp 07404 487674 with your model and symptoms — you will get a straight answer, not a sales pitch.
Frequently asked questions
Which Mercedes models do you cover?
Most of the range: C-Class (W203/W204), E-Class (W211/W212), CLK (W209), SL (W230), ML (W164), Vito (W639), Sprinter and others. If you are unsure, send the chassis or part number and we will confirm.
Will my existing keys still work after the repair?
Yes. We repair your original EZS rather than swapping it, so the key data is untouched. We bench-test your keys against the unit before returning it.
My key will not turn — is it the key or the ignition?
It can be either, which is why we test both. The key’s internal electronics wear out too. Bring or send both the unit and your keys and we will tell you exactly which side has failed.
Can you do this without the car coming to Basingstoke?
Usually, yes. Many EZS jobs are done by post, and we run mobile visits across London and the South East for cars that cannot move. Call first so we can plan the right approach.