My understanding is that the E/S switch controls a solenoid valve which switches a vacuum line ON/OPEN thus delaying the upshift on the box. The default is valve closed = S mode The E mode requires the valve to be open/energised by the switch which simply powers the solenoid valve circuit to switch it on. Your problem could lie with the vacuum supply or the solenoid or the switch. The switch is a common failure. It should be easy to test by bridging it. This should cause the solenoid valve to open (you might even hear it) and the box should then be in E mode. If this works all you need is a new switch. If not its the solenoid supply or the vacuum system. Do this test with the engine warmed up since there is also a transmission shift delay built in to help warm up the catalyst on a cold engine. this post may help but its a bit confusing? Proceed with caution since my info is gained from several sources on several different models and there may differences between models e.g. I'm not sure whether the solenoid is powered via a relay or not?? http://www.mercedesshop.com/shopforum/showthread.php?t=52931&highlight=e/s+switch
