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Greetings, I have observed that the radiator fans on my E270 vehicle are operating continuously at first startup.

This phenomenon occurs when the air conditioning and heating systems are both off. The temperature of the engine is within the acceptable range, and the amount of coolant is at an appropriate level.

I have conducted a diagnostic scan for fault codes and have determined that all systems are functioning properly. Could you kindly provide any recommendations or suggestions? It is possible that the temperature transmitter for the fan is defective.

The user expresses gratitude for the assistance provided.

This occurrence often arises when the fan control unit experiences a loss of CAN-bus connectivity with the engine or AC controller.
To safeguard the engine, the radiator fan(s) are operated at maximum speed. However, under normal circumstances, this scenario should typically lead to the generation of error codes. In any case, it is advisable to inspect the cables and connectors for potential issues such as faulty connections, corrosion, or misalignment of contact components in the plugs and sockets.

Instances have arisen in which workshops have opted to replace controllers solely based on error signals that indicated a lost connection, leading to a misinterpretation of the issue as a hardware (controller) malfunction. Numerous electrical issues may be attributed to mechanical factors, and I strongly recommend that those who want assistance do the necessary inspections independently. One especially challenging issue that has arisen is to the use of "Z-joints". In an effort to save costs, automobile manufacturers have implemented the practise of including joints inside cable harnesses, such as for the purpose of sharing a ground (GND) connection.
Indeed, there have been several instances of this phenomenon, leading to a range of challenges that are not always straightforward to resolve.

One arguable imprudent choice has been the use of slender wires in sensor harnesses that are not designed to accommodate substantial electrical currents. When a harness is bent in a casual manner, the tiny wires inside it get stretched to the extent that they exceed their breaking point, resulting in the formation of open circuits. Consequently, the outcome is inaccurate measurements from the sensors.

If the fan starts about 10 seconds subsequent to engine start, it is plausible that the cause may be attributed to insufficient air conditioning pressure or a malfunctioning air conditioning pressure sensor.

Do you own the iCarsoft diagnostic tool? Is it possible to assess the air conditioning system pressure in both idle and operational states of the vehicle, and what are the corresponding measurements obtained?

Thank you for the aforementioned ideas; I own the iCarsoft diagnostic tool. I will examine it.

During this period, I have once again occupied the vehicle, started its ignition, and activated the fans after a certain number of seconds. Subsequently, I saw a rapid increase in the temperature gauge, reaching 90 degrees Celsius immediately. then, the temperature increased to 120°C and then decreased to 90°C.

It is probable that the temperature sensor is the cause. What is your opinion, individuals?

Norm is a pulse-width modulation (PWM) device used for fan control purposes. It has a diagnostic signal grounding feature that enables the fan controller to effectively communicate fault information to the electronic control unit (ECU).
The LIN protocol may be considered a cost-effective option that offers sufficient speed, whereas the CAN protocol would significantly increase the overall cost of the controller.

The location of the coolant temperature sensor is inside the thermostat housing. I own the previous thermostat housing that was changed five years ago, and I want to attempt the transfer of the sensor to that housing at my earliest convenience.

What is the definition of LIN?

The Local Interconnect Network (LIN) is a communication protocol often used in automotive applications for connecting several electronic control units (ECUs) inside a vehicle. The system in question operates on a 12-volt power supply and uses serial communication. A single dominant device, such as an Electronic Control Unit (ECU), governs the operation of one or several subordinate devices, such as a glow controller and an alternator. The enslaved individuals alone transmit information in reaction to a solicitation from their overseer.

There exists a distinction between the Controller Area Network (CAN) and other communication protocols, whereby each device in CAN operates as a master by autonomously transmitting data without requiring explicit requests.

Please verify the functionality of the fan relay as it may be experiencing adhesive properties.

However, it is important to note that the introduction of muck might potentially disrupt the accuracy of the temperature readings. Hence, this is why I am emphasising the significance of the temperature sensor.