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CAN bus

Controller Area Network (CAN or CAN bus) is a vehicle bus standard designed to allow microcontrollers and devices to communicate with each other within a vehicle without a host computer.

CAN is a message-based protocol, designed specifically for automotive applications but now also used in other areas such as industrial automation and medical equipment.

Bit rates up to 1 Mbit/s are possible at network lengths below 40 m. Decreasing the bit rate allows longer network distances (e.g., 500 m at 125 kbit/s).

The CAN data link layer protocol is standardized in ISO 11898-1 (2003).[4] This standard describes mainly the data link layer (composed of the logical link control (LLC) sublayer and the media access control (MAC) sublayer) and some aspects of the physical layer of the OSI reference model. All the other protocol layers are the network designer's choice.


On-Board Diagnostics, or OBD, in an automotive context, is a generic term referring to a vehicle's self-diagnostic and reporting capability. OBD systems give the vehicle owner or a repair technician access to state of health information for various vehicle sub-systems. The amount of diagnostic information available via OBD has varied widely since the introduction in the early 1980s of on-board vehicle computers, which made OBD possible. Early instances of OBD would simply illuminate a malfunction indicator light, or MIL, if a problem was detected—but would not provide any information as to the nature of the problem. Modern OBD implementations use a standardized digital communications port to provide real-time data in addition to a standardized series of diagnostic trouble codes, or DTCs, which allow one to rapidly identify and remedy malfunctions within the vehicle.

Electronic control unit

In automotive electronics, electronic control unit (ECU) is a generic term for any embedded system that controls one or more of the electrical systems or subsystems in a motor vehicle.

Types of ECU include

  • Electronic/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 continue 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).