On my 06 E320 CDI, I have not been able to detect any rhyme or reason why sometimes I can push and hold the unlock button on the remote and open all the windows and sometimes I can't. It's inconsistent with both keys (good batteries in both). And, yes, I'm aware that I need to be close to the door.

Thoughts?

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14 E250 Bluetec "Sinclair", Palladium Silver on Black, 153k miles
06 E320 CDI "Rutherford", Black on Tan, 171k mi, Stage 1 tune, tuned TCU
91 300D "Otis", Smoke Silver, 142k mi, wastegate conversion

19 Honda CR-V EX 61k mi
Fourteen other MB's owned and sold
1961 Very Tolerant Wife

Sounds like an incomplete circuit or being out of range.
(Happens with my DVD remote)

Detector out of range of the signal "cone" ?
Failing detector?
Corrosion left behind from prior battery?
Membrane switch of the button starting to fail?

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78 W116 300SD 'Desert Rose' new as of 01/26/2014
79 W116 300SD 'Stormcloud' RIP 04/11/2022