Returning to my car at the end of a busy day at school, I pressed the unlock button on the key fob and the lights flashed as normal. Unfortunately, the doors failed to unlock
After locking and unlocking a couple of times more with the same result, I was able to unlock the driver's door with the key but that was it. All the other doors remained lock and I was unable to unlock them by pulling the interior door handle or activating the central locking button in the console.
To cut a long story short, these are the symptoms of a failed GM5 control unit - and specifically, the two relays in the box that control the door locking.
This is a common fault for the E46 and it appears that 15 years and 308000 miles is a very good life for this unit. The fix is either to replace the whole box (expensive) or replace the two relays (about 1.5 hours work by someone who knows what they are doing).
A repair is now scheduled and apart from the obvious inconvenience of being only able to access the car via the driver's door, through the windows or the boot, the car is perfectly functional
