Control unit

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Control unit

Control units (ECU = electronic control unit or ECM = electronic control module ) are electronic modules that are mainly installed in places where something has to be controlled or regulated . Control devices are used in all imaginable electronic areas in the automotive sector, as well as for controlling machines, systems and other technical processes. They are part of the embedded systems .


At the beginning of electronic engine control , control units were primarily used for ignitions; since 1987 they have also been used for the electronic control of diesel engines. Since around the mid-1990s, mechanical control concepts in combustion engines have been almost completely replaced by electronic control units.

Control devices that are visible to the user today are the speedometer in its new form as a combination instrument together with the rev counter and various other displays. Sensors such as tank level gauges and oil pressure gauges are now connected to their own control units which, among other things, implement long-term monitoring and also continuously monitor the functionality of the sensor itself by checking its output values ​​for plausibility .


Control units generally work according to the EVA principle . EVA stands for input – processing – output. Sensors are available for input . These determine a physical parameter such as B. speed, pressure, temperature, etc. This value is compared with a setpoint entered or calculated in the control unit. If the measured value does not match the stored value, the control unit readjusts the physical process using actuators so that the measured actual values ​​again match the target values. The actuators intervene in an ongoing process to correct it.

While "electronic ignitions" in the early years were still made up of discrete, analog electronic circuits, today's control units are usually provided with "self-intelligence"; that is, they consist of a stand-alone computer in the form of an embedded system . The size of this computer varies considerably depending on the complexity of its tasks, it ranges from a one-chip solution with a microcontroller (with built-in RAM and ROM memory) to multi-processor systems with their own graphics output system. The programming of most of the control units installed today can be updated by the workshop using reprogrammable flash memories .


In current vehicles, control units are connected to one another via various system buses ( CAN , LIN , MOST , FlexRay , Ethernet ). In this way, the devices exchange information system-wide about the operating status and other relevant data in the vehicle. In addition, the on-board diagnosis or a vehicle diagnosis system is connected via such buses (and possibly the K line ) . This allows external communication with the control units using so-called diagnostic devices (alternatively with normal personal computers plus a suitable interface ). The main question here is whether the control unit has detected and registered any errors in itself or in the sensors connected to it during the continuous self-tests. A workshop with a message such as "Short to ground at the tank sensor" can save a lot of investigation work. Diagnostic protocols such as KWP2000 or UDS are often used.

Due to the increasing complexity and demands on the software and the need for communication between the control units, OSEK-OS has established itself in Germany as a real-time operating system and communication standard. Another measure is the increasing standardization of the ECU architectures, for example in the AUTOSAR development partnership.

In the meantime, there are more than ten control units distributed over the entire vehicle in a normal vehicle. Modern luxury limousines sometimes have more than 100 control units installed. The range of microcontrollers used extends from 8 to 32 bit computers.

Development and software

Control units are rarely developed and manufactured by the automobile manufacturer. Mostly these are developed by automotive suppliers on behalf of the automobile manufacturer.

In order to ensure the interoperability of the different control units in the different variants of different vehicle models, the automobile manufacturer usually prescribes certain software equipment that the supplier has to use. The aim of this uniform software system is a smooth networking and integration of all control devices into an overall system.

This basic software configuration is generally referred to as the standard core of the respective manufacturer.

A development goal is always to react correctly to foreseeable extreme situations. These include, above all, the undervoltage , as a special case the start voltage pulse , as well as extreme temperatures in both directions.


  • Karl-Heinz Dietsche, Thomas Jäger, Robert Bosch GmbH: Automotive pocket book. 25th edition, Friedr. Vieweg & Sohn Verlag, Wiesbaden, 2003, ISBN 3528238763 (28th edition 2014, ISBN 978-3658038007 )
  • Kurt-Jürgen Berger, Michael Braunheim, Eckhard Brennecke: Technology automotive engineering. 1st edition, Verlag Gehlen, Bad Homburg vor der Höhe, 2000, ISBN 3-441-92250-6
  • Robert Bosch (Ed.): Autoelectronics Autoelectronics. 5th completely revised and expanded edition. Vieweg & Sohn Verlag, Wiesbaden 2007, ISBN 978-3-528-23872-8
  • Werner Zimmermann and Ralf Schmidgall: Bus systems in vehicle technology - protocols, standards and software architecture . 4th edition, Vieweg + Teubner, Wiesbaden 2010, ISBN 978-3-8348-0907-0
  • Tomasz Betlejewski: Data and control technical application repairs of control devices in the automotive industry Steuergerät24 Repair . 1st edition, Skiron Verlag, 2009

See also

Commons : Automobile computers  - collection of pictures, videos and audio files