I was coding the recently installed LED fog light bulbs yesterday and I noticed that all of the lights show a coding function in Bimmercode for cold and hot monitoring. So I am curious if any one can explain these monitors to me.

 

It tests the bulbs to see if they are functioning (basic answer). LED run at a much lower power so it usually triggers the warnings or flashes the bulbs. So people code the check out or buy bulbs designed to defeat the issue.

 

Checks the bulbs when it is not in use.

COLD CHECK: As Boneman said, this check makes the LED bulb to flash when it's turned off, since the power that is sent for the check function doesn't turn on any halogen bulb but LED.
If the LED bulb is low power consumption type, this check will return a burned bulb error.

WARM CHECK: Checks the bulb when it is turned on.
As Boneman said, if the LED bulb is low power consumption, when turning on the bulb the ECU will see that the consumption is lower than expected and will generate a burned bulb alert.

Best Practice:

Avoid cheap LED bulbs, use high consumption LED bulbs. High consumption LED eat less power than halogen bulbs.
Prefer CANBUS ready LED bulbs.
Prefer cold and hot checks deactivation (programming) over installing stuff like "load resistors". You should check bulbs life periodically.