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Features   |   Identification   |   Component Locations   |   How it Works

This section contains in-depth discussion of how various components of the MPI engine management system work together. This is not where to go if you're having problems and need to diagnose sensors or controls - head to the maintenance section for that.

Theory of operation:

Major systems:

ECM Revisions:
  • MMS 200: The MMS200 series was the first Engine Control Module (ECM) series for the 12v V6 engine, used in the Audi 100 through October 1992 production. It was adapted from the MPI Engine Management System for the Coupe Quattro and 90 Quattro 20-Valve and included On Board Diagnostic I (OBD-I) capabilities. The ECM itself is made by Bosch and contains an 8-bit microprocessor with 48kB system memory.
    Engine Control Modules:
    • 4A0 906 266 A
    • 4A0 906 266 AA
    • 4A0 906 266 AB
  • MMS 300: With this version, the MPI ECM was completely rewritten. This ECU was the first to incorporate adaptive learning functions such as oxygen sensor control. The MMS300 ECM was used from October 1992 to early 1993 production in Audi 80/90 and 100 models. The ECM is made by Hitachi and contains a 16-bit microprocessor with 60kB system memory. The ECM has the same four connectors as the MMS200 series ECM, but the terminal functions are different and the control module is not backwards compatible.
    Engine Control Module:
    • 8A0 906 266 B
    Successor versions to the MMS300 ECU using OBD-I are designated MMS311. The MMS311 series ECM was used in all 12v V6 models from 1993 to 1996, when OBD-II was introduced.
    Engine Control Modules:
    • 8A0 906 266 E
    • 8A0 906 266 H
    • 8A0 906 266 J
  • MMS 400: With this version, On Board Diagnostic II (OBD-II) was introduced for the A6 with manual transmission and front wheel drive. OBD-II included the addition of a second pair of heated oxygen sensors after the catalytic converters and new OBD programming. To accomodate new features, an additional 32 input/output pins were added to the ECM.
    Engine Control Module:
    • 8A0 906 266 D
    Successor versions to the MMS400 ECU are designated MMS411 and MMS411A. The MMS411 series ECM is used in 12v A6 and Cabriolet models from model year 1996 on; the MMS411A series ECM is used in 12v A4 models.
    Engine Control Module:
    • 8D0 906 266 A