Digital Motor Electronics (DME) is a microprocessor-based system that controls the ignition, the fuel injection, the oxygen sensor and numerous ancillary functions. DME provides raw data to an on-board computer that uses an alphanumeric display to provide you with information such as the average fuel consumption, the distance you can still cover with fuel in the tank, an average speed, outside temperature and more. 

In the industry, DME is often referred to as the Engine Control Unit (ECU), under the heading of Electronic Engine Management Systems. BMW also uses the term DDE (Digital Diesel Electronics) for diesel engine models instead of DME.

DME operates by continually monitoring such factors as engine temperature, speed, intake airflow, exhaust gas composition, and even the altitude. DME then literally fine-tunes the engine hundreds of times a second to provide maximum performance and efficiency. DME has a fail-safe program in the event of certain electrical faults. Current DME versions also have on-board diagnostics (OBD).

The two main tasks DME has to perform are (1) injecting the right amount of fuel and (2) providing a spark at the correct time. In order to do this, the system needs to know things about the engine's current state. DME can track dozens of different sensors, but every system needs to know three basic things: 

1. how much air is coming in
2. the position of the throttle, and 
3. how fast the engine is running. 

Using the information about how much air is flowing through the engine and how fast it's turning, DME uses a fuel map to determine how long each injector should stay open each cycle to inject the right amount of fuel. During part-throttle operation, the injector pulse-width is also modified by the readings from the oxygen sensor, a device that sits in the exhaust collector and determines how much oxygen is left over in the exhaust. Each cylinder is constantly adjusted to maximum operating efficiency under virtually all conditions. 

In the event of an electrical fault, DME can reconfigure itself to bypass the problem, and DME can diagnose itself for quick and efficient trouble-shooting.

Circuit diagram of early DME system

The core of a DME application are microprocessors. Microprocessors work at astonishing speeds. The core of central engine management in the current M3 executes nearly twenty million instructions per second (20 MIPS). Microprocessors also have a reputation for being extremely reliable. They are designed for a lifespan of at least 150,000 active hours. A car by comparison, is expected to survive 4,000 hours of use.

Since it first appeared in the late 70's, DME has evolved significantly over the years.

In 1979 new engine electronics, an industry first, was introduced in the BMW 633 CSi. The 3210cc engine in the 633 CSi got the DME (then called Electronic Engine Management) that later was to be used in all 6 Series cars and subsequent BMW models. 

In late 1986, BMW introduced a new 7 Series model equipped with a new, third-generation Digital Motor Electronics (DME III). Using over 30 sensors and interfaces, DME III can control fuel supply and ignition timing with precision. DME III compares actual data with targeted data. It determines changes in the conditions and adjust accordingly. It can detect and memorize malfunctions, and this information is saved and can be displayed during the next routine service. 

Most DME components are manufactured by Robert Bosch under the trade name Motronic. Here are some of the known DME version numbers:

• M1.0 Adaptive (24 pin) and (28 pin), Basic and Motorsport
• M1.1
• M1.2
• M1.3
• M1.7
• M1.7.2 and M1.7.2 w/ EWS-II
• M3.1
• M3.3, M3.3 w/ EWS-II, and M3.3 with air pump
• M3.3.1 and M3.3.1 w/ EWS-II
• M5.2 (OBD-II)
• MS41.1 (OBD-II)

Current DME systems, like those used in the new M3, are distributor-less electronic ignition systems. With solid-state distributors, each cylinder and spark plug has its own coil and is controlled by the DME, providing better combustion and fuel efficiency. DME also provides cylinder-specific knock control. As soon as the engine starts to knock, sensors inform the DME accordingly, which then changes the ignition angle and timing. As a side effect, DME control allows the engine to run on different grades of fuel without suffering any impairment.

DME includes an electronically controlled engine cooling system. This system has a "map" that tells the engine thermostat how to react in response to engine speed, load and outside temperature – rather than just coolant temperature. With this system, the engine can operate at higher temperatures under light-load conditions for enhanced fuel efficiency and heater effectiveness.

BMW Thailand technology page has a paragraph on Digital Motor Electronics (DME).

DME I circuit diagram and description.

Troubleshooting Electronic Engine Management Systems is a humorous but insightful description of what can happen with DME applications. 

Autospeed article on DME-like systems describes the principles of operation and troubleshooting tips.

Autorev briefly defines DME and other BMW technologies.

BMW Service lights page has a picture of service light combinations and an explanation of what the lights mean. Service lights are set by DME in response to certain operating conditions.