What are comfort modules? Control and most common faults

What are comfort modules? What is their possible purpose and principle of operation? We can find them in all cars produced today and optionally in older vehicles. What is worth knowing about them?



To put it simply, these are electronic devices whose primary task is to control work and directly supervise such systems as e.g. air conditioning system, electric windows, sunroof, central locking, factory alarm or electrically controlled exterior mirrors. The list of supervised systems depends on the vehicle equipment level and may additionally include, among others adjusting and heating seats, electric steering column position control or rain sensor control. In older vintage cars, we may encounter a complete lack of comfort modules or their optional presence. In such cases, the windows are opened and closed only manually, there is also no central lock.


Comfort modules can be controlled using car data exchange buses (CAN, LIN, MOST) or Bluetooth radio transmission. The simplest and slowest solution used to monitor comfort modules is the LIN serial communication bus (Local Interconnect Network). It was massively used in the years 1998–2000 and is currently no longer used, mainly due to the relatively low data transfer speed (up to 20 kb / s). The bus of this type was most often used to control air conditioning, electric window lowering and external mirrors, as well as to operate alarm systems and central locking. Since 2005, extensive CAN (Controller Area Network) buses dominate, among which the slower (Low Speed) and faster (High Speed) versions are distinguished. Modern CAN buses also support multimedia. In the case of very fast data exchange, an extensive bus called MOST (Media Oriented System Transport) is used to connect IT and multimedia systems. In the case of the latter, the data transfer rate is from 25 to even 124 kbps. However, such a high speed is reserved primarily for increasingly complex security systems.


The location of comfort modules in a particular car depends on the vehicle manufacturer. For example, in Audi and Volkswagen vehicles, the comfort module is located in a box located in the floor under the driver’s feet. On the other hand, the models offered by Renault should be looked for in the vicinity of the internal fuse box.


It is difficult to answer this question unequivocally, because potential defects may concern one specific system or several (damage to the so-called master node), among others due to the lack of power to the comfort module. In this situation, e.g. central locking or window control does not work. Similar problems can also occur after prolonged disconnection of the battery. The case with multimedia devices mounted in the car looks even different. In this case, the lack of their proper functioning may be caused by damage to the data exchange network, not the comfort module.


In the event of a failure of the comfort module, the basic tool is the diagnostic interface – on the diagnoscope screen we read the communication error with the controller. With this knowledge, you should first check the voltage flow by checking the fuses. The next step is to measure the voltage on the module supply plug: it should be within 8-12V. If there is no voltage, the problem lies with the vehicle’s electrical system. Incorrect operation of the comfort module can also be caused by moisture. Sometimes a return to its proper operation may occur based on the so-called hard reset, i.e. unplugging and re-enabling the module’s power connector. Another way of “manually” restoring the proper functioning of the comfort module is by disconnecting the negative pole of the battery for several minutes. When all attempts fail and the module is clearly damaged, it must be replaced. In its place you can mount a new or used module. It is important to remember that the serial numbers are compatible and that they must be re-encoded.

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Audi maniac, owner of upgrademyaudi.net and big fan of Audi cars. Maps, firmware, car audio installer
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