Quote:
Originally Posted by oldskewel
... I don't know whether the EWS interrogation requires the fob to be powered with a battery. ...
... So that shows it is possible, but I'm not completely sure yet whether the EWS in a diamond key has the same capability to work without a battery.
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It doesn't require the battery at all - as you indicated, the EWS transponder is powered by the RF field around the ignition lock.
BUT... the diamond key EWS transponder is built on the same PCB as the rest of the key-less entry circuit and relies on some of the components on that PCB (antenna coil, rectifier, capacitor, transponder I.C. etc.) so any damage to the PCB may result in a non-working EWS transponder.
Other transponder solutions (as used in some BMWs, V.W.s etc.) are based on a self contained transponders I.C. or micro-device and can be moved from key to key.