The W203 fan activates without the ignition key.

[MDMH757]

Greetings everyone,
Upon removing my key from the ignition, if one waits a few minutes, the radiator fan activates at maximum capacity; however, if the ignition is turned on again, it deactivates and operates properly without overheating. What might be the underlying reason for this?
I appreciate it.

[another_clean_sheet]

Greetings, the radiator fan is also associated with the air conditioning function. It does seem somewhat peculiar, however.

[vitessear3]

Is it a diesel engine? VWs perform this action when the EGR system requires a cleansing. If you operate the vehicle on the highway for 10 minutes, does it remain stationary? It has not been observed occurring on our 220 D, even at 150,000 miles.

[MDMH757]

Indeed, the 270 CDI undergoes a vigorous drive occasionally to assist in maintaining its cleanliness. Do Mercedes possess that as well? They appear to be disparate systems to me, although my knowledge of these or diesel engines is limited. I appreciate it.

[vitessear3]

It is uncertain whether Mercs perform this function, but VW vehicles do it to regulate the temperature of the valve and filter, which can overheat when contaminated with soot. My local Volkswagen dealership performed this routinely, and I suspected the thermostat was faulty, but a brief online search validated my concerns. Only likely pertinent if yours predates Adblue.