Electronic control unit

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An electronic control unit (ECU) is an embedded system in automotive electronics that controls one or more of the electrical systems or subsystems in a vehicle.

An ECU from a Geo Storm

Types of ECU include engine control module (ECM), powertrain control module (PCM), Transmission Control Module (TCM), Brake Control Module (BCM or EBCM), Central Control Module (CCM), Central Timing Module (CTM), General Electronic Module (GEM), Body Control Module (BCM), Suspension Control Module (SCM), control unit, or control module. Taken together, these systems are sometimes referred to as the car's computer (technically there is no single computer but multiple ones). Sometimes one assembly incorporates several of the individual control modules (PCM is often both engine and transmission).[1]

Some modern motor vehicles have up to 80 ECUs. Embedded software in ECUs continues to increase in line count, complexity, and sophistication.[2] Managing the increasing complexity and number of ECUs in a vehicle has become a key challenge for original equipment manufacturers (OEMs).


Key elementsEdit

  • Core
  • Memory
  • Inputs
    • Supply Voltage and Ground
    • Digital inputs
    • Analog inputs
  • Outputs
    • Actuator drivers (e.g. injectors, relays, valves)
    • H bridge drivers for servomotors
    • Logic outputs
  • Communication links
    • Housing
    • Bus Transceivers, e.g. for K-Line, CAN, Ethernet
  • Embedded Software
    • Boot Loader
    • Metadata for ECU and Software Identification, Version Management, Checksums
    • Functional Software Routines
    • Configuration Data

Design and developmentEdit

The development of an ECU involves both hardware and software required to perform the functions expected from that particular module. Automotive ECU's are being developed following the V-model.[1] Recently the trend is to dedicate a significant amount of time and effort to develop safe modules by following standards like ISO 26262.[3] It is rare that a module is developed fully from scratch. The design is generally iterative and improvements are made to both the hardware and software. The development of most ECU's are carried out by Tier 1 suppliers based on specifications provided by the OEM.

Testing and validationEdit

As part of the development cycle, manufacturers perform detailed FMEAs and other failure analyses to catch failure modes that can lead to unsafe conditions or driver annoyance. Extensive testing and validation activities are carried out as part of the Production part approval process to gain confidence of the hardware and software. On-board diagnostics or OBD help provide specific data related to which system or component failed or caused a failure during run time and help perform repairs.


Some people may wish to modify their ECU so as to be able to add more functionality to it. Most ECU's these days however come equipped with protection locks which prevent users from modifying the circuit or exchange chips. The protection locks are made in a way that, when circumvented, triggers DMCA liability. This in effect makes modifying the ECU by circumventing the protection illegal[4] except if done under an exception[5] to the DMCA.


  1. ^ a b National Instruments White Paper on Electronic Control Units Archived 2013-12-21 at the Wayback Machine
  2. ^ Ebert, Christof; Jones, Capers (2009-04-01). "Embedded Software: Facts, Figures, and Future". Computer. 42 (4): 42–52. doi:10.1109/MC.2009.118. Retrieved 2010-09-15.
  3. ^ Case, Lenny (October 2011). "Fast-tracking ECU development". Automotive Industries.
  4. ^ "Circumventing ECU protection being illegal". Wired. 2015-01-23.
  5. ^ "Federal Register". 2015-10-28.