I have a 1999 S320 which everything worked fine when I purchased it; then I changed the batteries in the keyless remote and everything stopped working (Doors and trunk locks) any suggestions? I have unhooked the battery and nothing changed.

 

with mine I first put key in ignition,then prees to open and hold till door locks or open.

 

Same thing happened to me.Replaced 2 batteries in my remote key. Made sure of battery orientation (+, -) . Didn't work. Bought batteries from__________. Long story short, removed new batteries and tested for voltage. Found out that one of the batteries has wrong polarity. I'm serious. Must have fried the internal components of remote. Now, my doors and trunk locks do not work, console lock/unlock switch not working. My other remote key elicits green/red flash of light on signal receiver on outside of door. will try disconnecting car battery or pulling several fuses out and put them back in, hoping things will reset. Will post results.