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2017 S550 Keyless Go Not Working - 'Key Not Detected'

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

Vehicle: 2017 Mercedes-Benz S550

I'm having a persistent problem with the Keyless Go feature on my 2017 Mercedes-Benz S550 (W222). When I try to start the car, I get a 'Key Not Detected' message, and I have to place the SmartKey in the designated slot to start it. The key fob itself works fine for locking/unlocking the doors remotely.

This happens with both of my keys, and I've already replaced the batteries in both fobs. The Keyless Go for unlocking the doors by touching the handle also works intermittently, sometimes it does, sometimes it doesn't. It's really inconvenient for a luxury car. What could be causing this electrical headache?

✓ 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 and intermittent Keyless Go functionality on your 2017 S550, especially after replacing key fob batteries, points to an issue with the vehicle's Keyless Go system components rather than the key fobs themselves.

Common Causes:

  1. Keyless Go Antenna Issues: The vehicle has multiple antennas (interior and exterior) that detect the SmartKey's presence. If one or more of these antennas fail or their wiring is damaged, the system won't detect the key properly.
  2. EIS (Electronic Ignition Switch) / EZS (Electronic Ignition System) Module: While less common, a fault in the EIS/EZS module, which communicates with the key and authorizes starting, can cause these symptoms.
  3. Rear SAM (Signal Acquisition and Actuation Module): The rear SAM often plays a role in Keyless Go functionality, especially for trunk access and sometimes overall system communication. A fault here can impact the system.
  4. Door Handle Sensors: If the door handle sensors themselves are failing, it can affect the Keyless Go unlocking feature, though it's less likely to cause the 'Key Not Detected' for starting.

Relevant OBD-II Codes (Mercedes-specific):

  • B1000 series codes: Often relate to internal control module faults, including EIS/EZS.
  • B2XXX series codes: Can indicate issues with antenna circuits or communication with specific Keyless Go components.
  • U0XXX series codes: Communication errors between modules involved in the Keyless Go system.

Troubleshooting Steps:

  1. Check for Interference: Ensure there are no strong electronic devices (e.g., cell phones, RFID cards) near the key fob or within the car that could be interfering with the signal.
  2. Test All Door Handles: See if the Keyless Go unlocking works on any specific door handles, which might help isolate an antenna issue.

When to See a Shop:

Diagnosing Keyless Go issues requires specialized Mercedes-Benz diagnostic equipment (XENTRY/DAS) to read fault codes from the EIS, SAMs, and Keyless Go control units. A dealership or a well-equipped independent Mercedes specialist can accurately pinpoint which antenna is faulty, if there's a wiring issue, or if a control module needs replacement. Given that it affects both starting and door unlocking, it's likely a central component or a widely used antenna, making professional diagnosis essential for your 2017 S550.

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