Door locking

I’m hoping you can help me with a problem concerning the door lock solenoid on the rear passenger door on a 2006 Vauxhall Zafira. The problem is that it won’t lock – you can lock the vehicle with the key or the remote, which locks all the doors but the nearside rear. The strange thing is that when you open the door from either inside or outside, it unlocks the remaining doors.

Thinking it was a faulty solenoid unit, I replaced it with a secondhand one, which made no difference. How would you go about manually testing the solenoid? I have a section of wiring that came with the secondhand plug, but I don’t know which wires to connect. Is it possible there’s another fault with the vehicle, or am I just unlucky to have bought a duff solenoid?

Although you may have been unlucky enough to have bought a faulty solenoid, having exactly the same symptoms would be unusual. The most likely culprit is the connecting wire between the vehicle body and the door solenoid. As opening the door manually unlocks the other doors via the central locking system, it appears that some connection between the solenoid and control system is still being maintained. The system also has a relay for locking and another for unlocking, but as the rest of the system works these can be discounted.

According to my data, the colours of the wires to the solenoid should be white, grey/white, black/green, grey and brown. The brown wire is the earth and I would first check this with a continuity meter on the vehicle to ensure it is making a good connection with the vehicle body. The white wire is fed from the unlock relay and should power the lock to open when live. The grey/white wire is from the lock relay and should power the lock to lock. The black/green wire will deadlock the lock and the grey wire is connected to the door ajar system. By connecting the brown wire to negative and the white wire or the grey/ white wire (not both at the same time) to positive, the solenoid should operate.