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2017 S550 - Key Not Detected, Won't Start Intermittently

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Eric V. · rep 0 · May 22, 4:16 AM · 1 replies · solved · Question

Vehicle: 2017 Mercedes-Benz S550

Hey everyone,

I'm having a very frustrating problem with my 2017 Mercedes-Benz S550 (W222). Intermittently, when I try to start the car, I get a 'Key Not Detected' message on the dash, and the car simply won't start. It's completely random – sometimes it works fine for days, then suddenly it acts up. I've already replaced the battery in both of my key fobs, thinking that was the obvious culprit, but the issue persists.

When it happens, I can't even shift out of park. If I wait a few minutes, sometimes it magically starts working again. Could this be an issue with the car's antenna, the EIS (Electronic Ignition Switch), or something more serious? I'm worried about getting stranded. Any advice on what to look for or what might be failing?

Thanks in advance!

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 22, 4:16 AM

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ClearTheCode admin answer:

The 'Key Not Detected' message on your 2017 S550, especially after replacing key fob batteries, points to a problem with the vehicle's Keyless Go system or the Electronic Ignition Switch (EIS) itself. This system relies on several components to recognize your key.

Here are the most likely causes:

  1. Keyless Go Antenna System: Your S550 has multiple antennas throughout the cabin and trunk that detect the key's presence. If one of these antennas or its wiring is faulty, it can lead to intermittent detection issues. Fault codes related to specific antenna circuits (e.g., B2200 series codes) might be stored.
  2. Electronic Ignition Switch (EIS): The EIS is the central component that authenticates your key and allows the car to start. A failing EIS can cause intermittent recognition problems. This is a critical and expensive component.
  3. Electronic Steering Lock (ESL): While less common for 'Key Not Detected' on newer models, a fault in the ESL can prevent starting. However, this usually presents with a 'Steering Lock Malfunction' message.
  4. Wiring/Module Communication: Intermittent communication issues between the EIS, Keyless Go control unit, and other modules can also cause this. This could be due to a loose connector or a faulty module.

When to see a shop:

  • This is a critical safety and security system. You should schedule an appointment with a Mercedes-Benz dealership or a specialized independent shop immediately.
  • They will need to use Mercedes-Benz STAR Diagnostics (XENTRY) to read fault codes from the EIS, Keyless Go module, and other relevant control units. These codes will be crucial in pinpointing the exact component that is failing.
  • Attempting to diagnose or repair this yourself is not recommended due to the complexity and security implications of these systems. A professional diagnosis is essential to avoid being stranded.
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