I would be interested to know if anyone has experience the following:

When temperature below zero the central locking fails to work. Car iced over, press the remote button and nothing happens. No indicator flash, no signs of any audible solenoid noise. Even boot release will not function. Changing remotes makes no difference.

To get into the car I have to use the emergency key and then kill the alarm. Once in everything then worked OK. I've done this emergency access from both sides/doors of the car and on each occasion the locks to not feel frozen. So all rather puzzling.

Anyway, thought main battery going down in cold weather so tested engine off volts, idle charge volts and charge current. Nothing really suspicious. As this Bosch battery had a 5 year warranty (just over two years in) took it back to Haldfords and got it tested. Tester came up with "Replace" (I think with 75% capacity left (or could have been 50%) Anyway new battery done and dusted.

Next cold snap same problem again.

What I find strange is that there is NO obvious electrical attempt to even blink the indicators, fire the solenoids. Boot release is dead as well and locks never feel frozen. This is really suggesting to me that in cold weather something is having a lazy lie in an refusing to wake up.

No the finer weather is hear and the latest MES Release has added more TEG reader function I'll connect up and see what if any errors are recorded.

An the error code stored is B1906 which as far as I can is possibly "lost communication with Door Multiplex control unit (door lock switch message)"

If this is the cause of the error it is possibly not a frozen lock issue but something in the door control unit itself or the wiring?

More research required.

Almost scared to say it but that's not something that's happened to me, other than before I changed the battery last weekend the car go completely dead until I slipped it in and out of reverse a few times which seemed to reset things.

Given that your problem only happens when it's below freezing the only things I can think of, and this is more than a little left field I know, is that since ice is an even worse conductor of electricity than water if there's a little water somewhere and it freezes maybe that's just enough to drop the current enough to convince the electronics that there's a problem.

Or maybe it's possible that the water freezes, expands and that's enough just to break the circuit.

Both just wild guesses though.

Well done that man -- the appliance of science and common sense

As the resistance of water reduces with temperature then the expansion (mechanical disruption) is the more likely electro-mechanical disruption cause.

I guess I need an environmental chamber for sub zero testing to properly debug this issue. OR a great hot summer, no rain, no car washing and then a sudden sub zero drop. (if only)

When the summer temps really get high then I'll look at popping the driver's door card (been there before) and check/dry/lube all connections for the next winter test

Re: Central Locking - Below Zero - Not Working

I think it is possible that the remote fob receiver is going off frequency in the cold. They are typically simple circuits that use a SAW (Surface acoustic wave, not the cutting tool) device for tuning. It could also be a bad solder joint in the receiver, in the cold parts shrink pulling the connection open. Not certain where the recever is in the Croma, but I think it's in the TEG (ignition switch) module. Need to get it out and apply some freezer spray. I'm afraid you are a bit too far away for me to help, used to be on the Dorset Hampshire boarde though.