Just picked up a CPO'd 05 E500 with "Keyless Go" among other options. I'm getting the error "key not recognized" for both keys... I've used both keys in the ignition, changed both keys batteries to fresh 2025's and talked to the Dealer about it... The owners manual suggests it's caused by radio frequency interference but that seems to be a stretch... I have a V1 in the car but it isn't supposed to be transmitting anything so not sure what's up... Is this a common issue with "Keyless Go" and if so, any quick fixes worth trying...?

 

That problem is usually caused by batteries, but since you have replaced them its probably not that. It could be an EIS... Which should be covered by CPO warrenty. I would take it in to the dealer to have them check it out.