Self-Diagnostics Feature: Notes

The self-diagnostic system used on 1991-94 V12 models is the Motronic DME M1.7 system. New features compared to the previous 1988-1990 DME M1.2 system includes an 88-pin control unit connector, integrated ignition circuit monitoring, and A/C compressor cut-out. DME control unit I supplies cylinders 1-6 and the identical control unit II supplies cylinders 7-12. To differentiate between them for diagnosis, pin No. 85 of control unit II is connected to ground. The associated components are mainly provided double. Exceptions are relay for oxygen sensor heating and engine temperature sensors.

The relay is activated by the DME control unit I and supplies the heaters of both oxygen sensors. This relay will be omitted in series production. On models without a relay for oxygen sensor heating, the sensor heaters are activated directly by the EKP relay. The engine temperature sensors for the DME control unit I and II are mounted together in one housing. The DME M1.7 makes it possible to precisely control fuel injection and ignition 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).
• Electronics vehicle module (EKM).
• On-board computer (BC).

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

• Injection control.
• Ignition angle control.
• Cold start control.
• Engine speed control.
• Acceleration enrichment.
• Dynamic torque cut-out.
• Catalytic converter protection function (ignition circuit monitoring).
• Adaptive emission (Lambda) control.
• Adaptive fuel evaporation control.
• Intervention in ignition and injection with ASC or MSR active.
• Characteristics map switchover for EH transmission.
• Relay control.
• A/C compressor cut-out.
• Self-diagnosis with defect code storage.

Following components supply the DME control units with input signals:

• Pulse generator - engine speed/position I and II. See Figure .
• Pulse generator - cylinder reference I and II. See Figure .
• Intake air temperature sensor I and II.
• Engine temperature sensor I and II (in one housing).
• Air mass meter I and II.
• Oxygen sensor I and II.
• Battery.
• EML control unit.
• EGS control unit.
• ABS/ASC/MSR control unit.

The outputs at the DME are connected via output stages. They supply the following components with the necessary signals:

• Injector valves for cylinders 1-3-5 or 7-9-11 (group 2).
• Injector valves for cylinders 2-3-6 or 8-10-12 (group 1).
• Ignition coil I and II.
• Fuel evaporation control valve I and II.
• EKP relay I and II.
• Main relay (control unit supply) I and II.
• Oxygen sensor heater relay (only on DME control unit I).
• Oxygen sensor I and II.
• CHECK ENGINE light.
• Air Mass Meter I and II.
• EML Control Unit.
• EGS Control Unit.
• ABS/ASC/MSR Control Unit.