Central Locking Won't Work After A Few Hours - CL500 C215 Facelift

RBT252

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Your Mercedes
CL500 C215 Facelift x 2
CL500 2003 facelift -.My central locking stops working after a few hours and I need to use the blade key to gain entry.

When I open the driver's door with the blade key the alarm goes off and central locking starts to work via the key fob and the lights on the car flash as normal, sometimes. 50% of the time the key fob does nothing, I need to wait until the alarm stops and for the alarm lights to stop flashing. This takes about 20 minutes and when I try the Key fob it works as it should.
However, after around 8 hours, my key fob stops working again, no flashing car lights too. I need to once again use the blade key and repeat the process I outlined above.

The CL500 has both radio and infrared signals from the key fob. I have noticed that after around 6 hours the radio signal seems to be put to sleep first, this means I need to get close to the car, around 6 ft for the infrared signal to open the car but after another couple of hours that goes to sleep too, meaning I need to use the blade key to open the door.

What have I tried
I replaced the batteries in both my key fobs, this made no difference.
New car battery
STAR found no faults
I replaced the PSE Pump, this made no difference.
I bought a replacement rear SAM, but this has yet to be fitted as the garage is having problems with their STAR
I have reached out to companies that repair the electronic ignition switch (EIS) to see if the EIS could be causing the issue, but none of them had heard of this problem before.
My Mercedes Indy garage has never heard of this problem before and they spoke to a Mercedes Master Mechanic who had also not heard of this problem before.
 
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