S40 0/4: Rear driver's side door will not lock

[paulmansfield]

All the other doors lock and unlock, but the rear driver's side stays the same, unlocked. Is this a case of get a new lock unit for it, and can I do it myself?

[iainmd]

It it most likely to be a failure of the lock unit unless the electric window doesn't work either in which case it could be the door electronic module. Other possibility is the wiring but I would expect the lock unit to be the culprit. My old S40 went through two lock units in its later years.

The lock unit is, I think, coded to the car. If you want to try to repair it yourself you can disassemble it and try to replace the faulty component but otherwise it's a dealer job.