Looks like my problem (with a Granvia), lots of info on the net most seems to suggest and I quote "What I did to get it to open (refer to the photo): I tried disassembling the 'Slide Door Closer' - the black box above the "clamper" motor in the top left. It contains a couple of relays and presumably tells the "clamper" motor when to switch on and when to switch off, using microswitches invisible behind the inner door skin as sensors. It gets its power via the yellow and white+red wires in the corrugated plastic conduit and is connected to the spring contacts in the front-edge of the door-frame. The voltage on the line from the door contacts is odd - its 3.5v when the white connector near the front edge is disconnected, but when connected there's no voltage at the "black box" connector - weird! With the white connector disconnected, I applied 12v from a spare battery across the yellow and the white+red leads - to my disappointment, nothing happened. But when I reconnected the white connector (with the 12v disconnected), the "clamper" motor suddenly whirred into life and the door latch could be opened!