Self-Diagnostics Feature: Notes

The self-diagnostic system used on 1988-90 V12 models is the Motronic DME M1.2 system. In this system, 2 Digital Motor Electronics (DME) control units operate independent of each other with 6 cylinders. If not otherwise indicated, the explanations therefore refer to only one row of cylinders. DME control unit No. 1 supplies cylinders 1-6, the identical control unit controls cylinders 7-12. As a differentiation during diagnostic mode, pin No. 40 on control unit No. 2 is connected to ground. In most cases, the associated components are fitted double with the exception of relays for oxygen sensor healing and engine temperature sensor. Oxygen sensor heating relay is assigned to control unit No. 1. The engine temperature sensor is provided double but is mounted in one housing.

DME M1.2 makes it possible to precisely control injection and ignition also under variable operating conditions. The system also operates in conjunction with other systems such as:

• Electronic throttle control (EML).
• Electronic transmission control (AEGS).
• Automatic stability control (ASC).
• Engine drag torque control (MSR).
• Antitheft system (DWA).
• Instrument cluster.
• On-board computer.

The DME Motronic system assumes functions which are listed briefly here and are described in more detail in the following:

• Injection control.
• Ignition angle control.
• Cold start control.
• Engine speed control.
• Oxygen control.
• Tank vent control.
• Characteristic switchover for EH transmission.
• Intervention in ignition and injection with ASC or MSR active.
• Relay controls.
• Self-diagnosis with defect code storage.

Following components supply the DME control units with input signals:

• Pulse generators - engine speed/position, I and II.
• Airflow meters I and II.
• Intake air temperature sensors I and II.
• Temperature sensors - engine I and II (in one housing).
• Pulse generators - cylinder reference point, I and II.
• Oxygen sensors I and II.
• Battery.
• EML control unit.
• AEGS control unit.

The outputs at the DME are connected via output stages. The following components are supplied on the negative side:

• Fuel injector valves, cylinders 1-3-5 or 7-9-11 (group 2).
• Fuel injector valves, cylinders 2-4-6 or 8-10-12 (group 1).
• Ignition coil.
• Fuel evaporation control valve.
• Fuel pump relay.
• Main relay (control unit supply).
• Oxygen sensor heating relay (DME control unit I only).
• Defect light.