Similar, but not the same, as post number 7797020. After a routine, eventless, map update to my nuvi 54LM, without an SD card, only major roads are shown, crudely, in the map display and my location is shown in the middle of an area absent of any detail of minor roads; the memory is reported as being full, and searching for an address returns the error message 'map data is not available'. Before the update there was no warning that the internal memory was nearly full and to consider adding an SD card, so I didn't install one. The previous map was CN Euro NTU 2022.1; the new, wonky, map is CN Europe NTU 2026.30 (disc image file D6159330A.img). The 'verification' steps show that the updated map is correctly present. I have found it impossible to go back to the previous working map. There is no option to install a smaller map e.g. UK and Ireland only. I have deleted the new .img, .gma and .unl trio of files.from the internal memory, then installed a 32GB SD card, and then re-installed the map (CN Europe NTU 2026.30, the only map which is offered) - but the map was again downloaded into the internal memory, ignoring the SD card. I have deleted the new trio of files again from the internal memory and I have replaced them with a trio of iles corresponding to an earlier Europe map from another device which works OK - but there is no change from the corrupt behaviour which started after the 'routine' update. I cannot find any alternative Operating System software to install. I cannot find any means to initiate a 'factory reset'. I have searched the Garmin Support pages, and I have tried all of the suggestions and nothing remedies the situation. I have de-registerd and then re-registered the device. The nuvi 54LM model is not in the list of models which have been rendered redundant with the passage of time. Any ideas, anyone?