[Ian M Davis]

I have attached a wiring diagram for a 3 door 207. The left door is block 6206. The right door lock (6206) motor and left door lock motor are wired in parallel so if the right door lock is working it would suggest the central locking system is working so I would concentrate on the connection to the left door. The wires you need to check are: 6204 and 6205. If the wires are broken it most likely to occur near the hinge. The best thing would be remove the door lining and measure some voltages at the lock's plug 6v MR (6 pin brown)

Other possibilities are a faulty door lock motor/activator or a bad earth (EC37). I have attached a earth location diagram.

 

[Ian M Davis]

Thank you for the messages. I have realised that this issue has started after my battery went flat and I had to boost it to get going. Could this have been the problem?

A flat battery can corrupt the BSI but I don't think that is the case with your car. The wiring diagram shows that the two front door lock actuators are wired in parallel so if the BSI had been corrupted neither door would lock.