This article may be confusing or unclear to readers. In particular, the article is not consistent in its use of the terms "unit" and "module" to describe the same devices, and lacks coherent structure, especially in the lists, both bulleted and in paragraph form. (February 2015) (Learn how and when to remove this template message)
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).
Some modern motor vehicles have up to 80 ECUs. Embedded software in ECUs continues to increase in line count, complexity, and sophistication. Managing the increasing complexity and number of ECUs in a vehicle has become a key challenge for original equipment manufacturers (OEMs).
Control unit vs. control module
Mainly, "control unit" and "control module" are used synonymously. Some manufactures prefer one over the other. Some manufactures use both terms with no differentiation. Technically speaking, there are no differences between them.
One probable explanation for the synonymous use of both terms: Since the abbreviation for Electronic Control Unit (ECU) and Engine Control Unit (ECU) are the same, some manufactures chose to use Engine Control Module (ECM) instead. This may have lead to the further use of "control module", instead of "control unit", for those devices later developed, i.e. Powertrain Control Module, Brake Control Module, etc.
- Door control unit (DCU)
- Engine control unit (ECU) — not to be confused with electronic control unit, the generic term for all these devices
- Electric Power Steering Control Unit (PSCU) — Generally this will be integrated into the EPS powerpack.
- Human-machine interface (HMI)
- Powertrain control module (PCM): Sometimes the functions of the Engine Control Unit and transmission control unit (TCU) are combined into a single unit called the Powertrain Control Module.
- Seat Control Unit
- Speed control unit (SCU)
- Telematic control unit (TCU)
- Transmission control unit (TCU)
- Brake Control Module (BCM; ABS or ESC)
- Battery management system (BMS)
- Supply Voltage and Ground
- Digital inputs
- Analog inputs
- Actuator drivers (e.g. injectors, relays, valves)
- H bridge drivers for servomotors
- Logic outputs
- Communication links
- 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 development
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. Recently the trend is to dedicate a significant amount of time and effort to develop safe modules by following standards like ISO 26262. 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 validation
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 ECU. 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  except if done under an exception to the DMCA.
- National Instruments White Paper on Electronic Control Units Archived 2013-12-21 at the Wayback Machine
- 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.
- Case, Lenny (October 2011). "Fast-tracking ECU development". Automotive Industries.
- "Circumventing ECU protection being illegal". Wired. 2015-01-23.
- "Federal Register". 2015-10-28.