Notes for Car Repair (Mercedes, BMW, VAG, etc.)

SEO-based writing by Laura, for car repair incl. OBD diagnosis, coding, programming…. for Mercedes Benz, BMW, VAG group vehicles, etc.

  • Diagnosis

OBD stands for “On-Board Diagnostics.” It is a computer-based system originally designed to reduce emissions by monitoring the performance of major engine components.

A basic OBD system consists of an ECU (Electronic Control Unit), which uses input from various sensors (e.g., oxygen sensors) to control the actuators (e.g., fuel injectors)  to get the desired performance.  The “Check Engine” light, also known as the MIL (Malfunction Indicator Light), provides an early warning of malfunctions to the vehicle owner. A modern vehicle can support hundreds of parameters, which can be accessed via the DLC (Diagnostic Link Connector) using a device called a scan tool.

There are two kinds of on-board diagnostic systems: OBD-I and OBD-II.
OBD-I: the first generation OBD systems which were developed throughout the 1980s.
OBD-II: first introduced in model year (MY) 1994 vehicles, and became a requirement for all cars and light trucks starting with MY1996.

  • Coding (e.g. BMW)

It is a process utilized by BMW, which groups system specific operating requirements (Data) together and then assigns a label/code to each of these groups of data. The various groups of data are all pre-loaded into system specific “codable” control modules, along with a basic set of operating instructions (Program).

There are various types of operating requirements such as; O2 sensors, emissions controls, fuel type, Manual or Auto transmission.

The procedure of assigning one specifically labeled group of data to the operating program of a specific control module/component is referred to as “coding”. Coding allows a specific set of data already present in the module to be selected.

A “codable” control module has a basic operating program already installed along with several specific variations of operating data. The coding process allows a specific set of operating data to be assigned to the basic operating program of that module/component, with respect to its specific application.

Coding can be performed for some systems/components via ISTA/P or the older DIS/Plus/GT1/SSS device. By entering a variant code via the device, selecting customer specific operational settings from a list of available features (VKM) or automatically by selecting a specific coding process.

Note: Codable control modules/components are system specific, which means that not all control modules are codable.

  • Programming (e.g. BMW)

It is a process utilized by BMW to load application/system specific operating instructions. Programming loads control functions instructions into a specific control module.

(Program) into a module/component which already has the systems operating requirements (Data) installed, plus it can be used as a means of updating data and operating instructions previously installed in a control module. Basic programmable control modules have a pre-defined set of operating data already installed which allows the module to be fairly generic until a specific operational program is installed.

The ability to program a module is limited to the number of times it has already been programmed and the hardware version of the control module itself.