It probably sounds really stupid but I hadn't realised that my C4 has power locks. The penny dropped when I took the door card off to inspect the passenger lock and I saw the actuator in the base of the door. They haven't been working since I had the car so I hadn't really missed them but now I know that they are there I feel they should work. Ignorance really is bliss.
Everything mechanically looks ok but neither side work so the first thing to do was to check the appropriate fuse which lurks under the passenger side dashboard beneath the 'hush pane'l/light surround in the auxiliary fuse box. Here....

The hush panel is the black plastic box that is screwed to the upper part of the dashboard with two 7mm screws. A third screw is hidden behind the fuse panel at the right hand side of the dashboard.
You have to remove the three Torx head screws first which releases the main fuse box surround....

... and the third 7mm screw holding on the hush box is found at the lower right...

After releasing the velcro that holds the red dash material round the hush box, the box can be manoeuvred down to reveal the auxiliary fuse panel, centrally placed but far in the distance....

You need to be a bit of a contortionist to get to it and see what's going on, but the door lock fuse is the second fuse from the left (blue 15 Amp) - fortunately at the front.
The fuse was blown but disappointingly fitting a new one hasn't fixed anything so further investigation is required. Probably new actuators ...Let's see what Rockauto can come up with....
Everything mechanically looks ok but neither side work so the first thing to do was to check the appropriate fuse which lurks under the passenger side dashboard beneath the 'hush pane'l/light surround in the auxiliary fuse box. Here....

The hush panel is the black plastic box that is screwed to the upper part of the dashboard with two 7mm screws. A third screw is hidden behind the fuse panel at the right hand side of the dashboard.
You have to remove the three Torx head screws first which releases the main fuse box surround....

... and the third 7mm screw holding on the hush box is found at the lower right...

After releasing the velcro that holds the red dash material round the hush box, the box can be manoeuvred down to reveal the auxiliary fuse panel, centrally placed but far in the distance....

You need to be a bit of a contortionist to get to it and see what's going on, but the door lock fuse is the second fuse from the left (blue 15 Amp) - fortunately at the front.
The fuse was blown but disappointingly fitting a new one hasn't fixed anything so further investigation is required. Probably new actuators ...Let's see what Rockauto can come up with....

