1997 Astra Estate GLS, 1.6 litre, 16 valve Ecotec engine, 84000 miles on speedo. Car is recently acquired.

Basically, the central locking doesn't work. Failure at all four doors. Failure with key operated in either front door.

Although the driver's door lock is a bit stiff when the key is turned, I suspect that this is simply down to lack of lubrication in this particular lock & not actually causing the problem. The front passenger door lock is OK. At night, when the key is rotated in the lock, the interior light does momentarily dim - which tells me that the at least one door solenoid is working & that the C/L fuse is intact (obviously, I can easily check just this fuse with a meter).

So, what's the likely cause? Gummed up mechanics on all four doors, a failure of the C/L control unit or a sticky / failed C/L relay? Checking out the first involves a lot of (possibly wasted) effort - not that finding, removing and testing the C/L control unit is much easier either.

So the benefit of the experience of others is requested on this, please.