If the back door locks are not locking when it's cold outside and you push the lock button, it's possible that there may be an issue with the door lock mechanism.
Here are some troubleshooting steps you can try:
Lubricate the lock mechanism: Cold temperatures can cause the lock mechanism to stiffen up, making it difficult to engage. Try using a silicone-based lubricant on the lock mechanism to see if that helps.
Check the door seal: If the door seal is damaged or not properly installed, it can cause the lock mechanism to not engage properly. Inspect the door seal to ensure it's in good condition and properly installed.
Check the door latch: The door latch is the mechanism that holds the door closed. If the latch is damaged or not functioning properly, it may prevent the lock mechanism from engaging. Check the door latch for any signs of damage or wear and have it replaced if necessary.
Check the electrical connection: If the door lock mechanism is controlled electronically, go to locksmith N5 to check the electrical connection to ensure it's secure and not damaged.