For the past two years, my 2004 Mercedes SL55 AMG has had an intermittent issue with the central locking system. After parking and locking the car, I sometimes cannot unlock it, either using the key fob or the keyless system on the door handle. The car seems to fail to recognize the key. The key fob itself is functioning properly—I can see the red light when I press it. However, to access the car, I have to use the physical key blade.

When I open the door with the key blade, the car’s alarm immediately goes off. After I insert the key into the ignition, the car starts without a problem, but the start button, along with all convenience functions (windows, lights, instrument clusters), remain unresponsive for about 10-15 seconds. After that period, everything returns to normal and the key functions perfectly, allowing me to lock and unlock the car as usual.



The issue reoccurs unpredictably after some time has passed since locking the car. It can happen after as little as 5 minutes or longer. Both the car battery and the key fob battery are new, and there’s no sign of battery drain. No relevant codes show up on the scanner.



Attempts to Resolve:



1. I have already replaced the trunk lock and passenger-side door lock a couple of years ago.

2. The only lock I haven’t replaced is the driver’s side door lock, but it works fine when the system is operational.

3. I’ve had the car checked by an independent specialist, and EIS related codes came up during the STAR diagnostic. When we delete these codes, initially car behaves perfectly fine. Then it goes crazy again because codes came up right away.

4. I’ve also taken it to a dealer, and they found some codes related to the door locks, recommending the replacement of all door and trunk locks for a quoted $6,000, which I declined. I tested a theory that if I don’t use the pse pump, meaning if I don’t lock and unlock the car, it should throw and codes therefore it should affect how the car behaves. It didn’t affect it. No codes related to pse pump if I don’t use it at all and no difference.



Additional Observations:



• The car starts fine despite the initial unresponsiveness.

• This issue does not seem to be well-documented in any forums, and I’ve attempted to reset the lock system, but nothing has worked so far.



LCP-Lower control panel

B1074: Fault in CAN communication with the control module 'N73 (Electronic Ignition Switch (EIS/EZS) control module)



Dr-side SAM-Driver signal acquisition and actuation module

B1074: No CAN message is received from the control module Electronic Ignition Switch (EIS/EZS)' or 'Central Gateway (CGW/ZGW)



Pass-side SAM-Passenger-side signal acquisition and actuation module B1074:

No CAN message is received from the control module 'N73 (Electronic Ignition Switch (EIS/EZS) control module)' or 'N93 (Central Gateway (CC ZGW) control module)



REAR SAM-Rear signal acquisition and actuation module B1074:

No CAN message is received from the control module 'Electronic Ignitic Switch (EIS/EZS)' or 'Central Gateway (CGW/ZGW)



After almost 3 years dealing with this, I finally sent out my EIS module to ECU Pro and they sent me a new used one that they programmed it for my car. That fixed all my issues. I was shocked. I am really happy about this result and wanted to share in an attempt to help someone having similar issues. Definitely suspect the EIS module if you are having inconsistent problems including keyless go. I’ve head that these modules are not great. I hope this helps someone. Good luck!