The back door can be locked/unlocked and opened/closed by the following procedures.
Automatic door locking and unlocking systems
Locking and unlocking the back doorOverhaul
1. REMOVE OIL PUMP RELIEF VALVE
(a) Remove the plug, spring and relief valve.
2. INSPECT OIL PUMP RELIEF VALVE
(a) Apply a light coat of engine oil to the oil pump relief valve
(b) Check that the valve falls smoothly into the valve hole by
its own weight.
If it does not, replace the relief ...