I’m having a weird electrical issue with my 2003 E55 AMG (W211). It started when the key fob suddenly stopped working — no remote lock/unlock, and the push-to-start button says “Key Not Recognized.” However, the car still starts and drives perfectly using the physical key in the ignition (after waiting 2–3 seconds for the dash lights).

What I’ve Done So Far:

• The rear Battery Control Module (BCM) had heavy corrosion on both the module and the connector.
• I cleaned everything thoroughly with electrical contact cleaner.
• I checked:
  • Both front and rear batteries – they are fully charged.
  • Alternator – it’s working fine (charging at ~14.4V).
  • Fuses – all are good.
• I replaced the BCM with a used one from eBay:
  • With the used BCM, the key fob didn’t work at all.
  • Switched back to my original (cleaned) BCM, and the key fob worked for 5 seconds, then stopped again.
• I also tightened a small red wire next to the main battery wire (it was loose).
• I can open/close the trunk via Otofix scanner, but trunk buttons don’t work manually.
• Also getting random ESP and SRS messages.
• The sunroof stops mid-way and requires repeated presses to fully close.
• The key fob buttons are now completely unresponsive, even though the red LED on the fob lights up.

Thinking about taking it to the dealership and get it checked out.

I have replaced voltage regulator aswell