I thought it worth getting to the bottom of EKA disabled on a v.37 BeCM/ GEMS 1998. To simulate force entry I locked the car on the fob, waited for the alarm to arm, and then pulled the sill button to get to engine disabled. EKA entry has been done via Nano, I didn't attempt to do this via the door lock.
First off I tried with EKA enabled, just to be sure when I disable the engine I could get back with a. the Fob, and b. the EKA code, and yes, all fine - dash message "engine disabled enter the EKA or press the remote". Since I hadn't gone battery flat then the fob signal didn't need synching. I tried to change the EKA to "disabled" in the BeCM while the engine was disabled, but it didn't accept the change in that state.
Then I disabled EKA, wrote settings, came out and went back in again - EKA disabled still. I locked the door with the fob, opened with the sill button. Turned the ignition on, this time "engine disabled, press the remote". BUT, when I went into the BECM at this point the EKA option is marked "enabled". After entering the EKA code, and going into BeCM/ Alarm the EKA setting had now reverted to "Disabled". So it appears that the BeCM always leaves the backdoor open for EKA entry, even if the EKA option has supposedly been disabled, and it doesn't actually ask for the EKA on the dash.
To test the key blade as a means of deactivating the engine disabled state:
i.with EKA enabled, simulated engine disabled, the key in the door unlocks only the driver's door, and does nothing to cancel the engine disabled message on the dash - as expected then
ii.with EKA disabled - the key in the door opens all 4 doors, and does actually cancel the engine disabled state, and the car drives away...
So it looks as if when you disable EKA in the BeCM you have 3 options to mobilise the engine: i. Remote fob (as per the message centre) i. the EKA (even if not asked for) ii. the key in the door (also not requested).