Description

The following description refers to the digital engine electronic system (Motronic) DME M 1.2 on the 12-cylinder engine M70.

In this system, two DME control units operate Independent of each other each with six cylinders. if not otherwise indicated, the explanations therefore refer to only one row of cylinders.

The DME control unit I supplies the cylinders 1 ...6, the identical control unit lithe cylinders 7...1 2. As a differentiation during diagnostic mode, Pin 40 on control unit II is connected to ground. In most cases, the associated components are fitted double with the exception of:
- Relays for oxygen sensor heating and
- Engine temperature sensor.

The oxygen sensor heating relay is assigned to the control unit I. The engine temperature sensor is provided double but is mounted in one housing.

The DME 1.2 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
which can influence the entire engine control system depending on requirements.

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
- Intervention in ignition and injection with ASC or MSR active
- Characteristic switchover for EH transmission
- Relay controls
- Self-diagnosis with defect code storage

The 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 lamp (US only)

Injection Control
The intake air flows through the air flow meter free of backpressure and pulses. Here the volume of air Is registered independent of the air temperature, air humidity and altitude. Based on the engine speed, air volume and engine temperature, the DME control unit then calculates the correct injection timing and ignition angle. The mixture is changed by the opening period of the fuel injector valves.

Air Flow Measurement
During operation, a heated platinum filament is subjected to the flow of intake air in the inner tube of the heating filament of the air flow meter (HLM). Heat is dissipated from the heating filament by the flow of air. This heat loss is compensated by controlling the heating current. At the same time, the power supply also flows via a precision resistor whose voltage drop represents a direct measure for the volume of intake air. Air temperature fluctuations are registered by a compensation resistor and taken into account during the measurement procedure. After switching off the engine, the heating filament is subjected to an increased current surge for approx. 1 second in order to bum oft any impurities on the filament.

Types of Injection
Each group of three injector valves is driven by one output stage. This arrangement makes it possible to divide the injection cycle into groups. This also ensures restricted engine operation in the case of failure of one group.

Parallel Injection
Parallel injection refers to simultaneous drive of six injector valves per turn of the crankshaft and takes place only when the cylinder reference point sensor supplies no signal.

Semisequential Injection
As of a speed of 600-800 rpm, fuel is injected only once per 720° crank angle into one cylinder group. This enables precision metering of the amount of fuel since the injector valves need not be activated so often. Switchover to semisequential Injection (in three cylinders) takes place as soon as the referenced point sensor (at ignition line 6 and 12) detects a signal. If this is not the case during the start phase, switchover takes place after torque cut-out is activated once (increase engine speed, then run at idling speed).

Engine Speed Control
Idle speed control and maximum engine speed limitation are achieved by the position of the throttle valve, EML assumes control - refer to EML functional description.
The DME receives the idle and full load signals from the EML control unit.

Cold Start Control
During the start phase, an increased quantity of fuel is injected three times for each cylinder group for up to 5 turns of the crankshaft. This function is dependent upon the engine temperature.

The initial injected quantity is then reduced depending upon the temperature and engine speed in order to avoid an excessively rich mixture. If start is repeated within one minute, the complete initial quantity is no longer injected.
After the engine has started (as of approx. 600 rpm) fuel is injected only once per turn of the crankshaft and cylinder group. This means that during the first turn fuel is injected in cylinders 2-4-6 and during the second turn in cylinders 1-3-5. The cylinders 8-10-12 and 7-9-11 are also supplied offset by 60° crank angle.

During the warm-up phase up to an engine temperature of 70 °C the injection timing is also correspondingly extended, dependent upon the engine speed and temperature. These values are programmed in the control units.

Fuel Evaporation Control for Models with Catalytic Converter
While being mixed with fresh air, the fuel vapours are directed to the cylinders via an activated carbon filter. Installed in the fuel evaporation line leading from the activated carbon filter to the air collector is a valve which restricts or enables the fuel vapours depending upon the current operating status. The electrical drive of the valve is dependent upon engine speed and load, separately for both rows of cylinders. The air release cycle involves 16 clock stages and begins as soon as the oxygen control system is active. On completion of the cycle, the valve is dosed for approx. 5 min. When power is not applied, the valve is only dosed by the non-return valve. If not supplied by the DME control unit, the valve opens as the vacuum in the air manifold increases.

Oxygen Control for Models with Catalytic Converter
To maintain the optimum degree of efficiency of the catalytic converter, this system aims at achieving the ideal air-fuel mixture (oxygen ratio = 1) for combustion. The heated oxygen sensor is used for this purpose measuring the remaining oxygen in the exhaust gas and transferring this value in the form of sinusoidal signals to the control unit. Here, the mixture composition is correspondingly corrected, if necessary, by changing the injection timing. In the case of failure of an oxygen sensor, control is provided by the DME control unit with a fixed programmed substitute value (0.45 V).

Since a temperature of approx. 300 °C is necessary for efficient operation of the oxygen sensor, power is supplied to the two heating resistors in the oxygen sensors via one relay. The relay is activated by the DME control unit I.

In models without a catalytic converter, the CO setting can be corrected with a potentiometer (on the HLM).

Drive-Away Protection
When the driveaway protection facility is active in the on-board computer (cede entered) or when the antitheft system is armed a signal (> 10V) is sent to the DME control units which consequently switch off the ignition and injection.

Automatic Stability Control ASC
The automatic stability control unit is integrated in the ABS control unit. It operates in conjunction with DME and EML.

Wheel slip at the drive wheels is registered by the wheel sensors and signalled to the ABS control unit. Consequently, the EML control unit is instructed to reduce the throttle opening. If the wheel slip is still too high, the DME control unit is instructed to retard the ignition timing. The ignition and injection can be switched off temporarily as a further measure.

Engine Drag Torque Control MSR
In the same way as the ASC, the MSR is also integrated in the ABS control unit. The engine is influenced by DME and EML.

A signal is sent to the OME control unit when Increased slip occurs at the drive wheels when the vehicle is coasting. Consequently, the torque cut- out is deactivated. In addition, the EML control unit is instructed to adapt the position of the throttle valve until the wheel slip is within the permissible range once again.

Performance Characteristic Switchover for EH Transmission
During the shift procedure, the AEGS control unit sends a signal to the DME control units which set the ignition angle towards retard. This ensures a smooth transition to the newly selected drive range.
As soon as the torque converter clutch unit is engaged, the DME control units are instructed to switch over to a different ignition angle characteristic.

Self-Diagnosis
The task of the self-diagnosis feature is to detect faults in the OME and subsequently store defect codes. Troubleshooting is assisted by the self- diagnosis feature in the form of status inquiries and component activation.

In the case of failure of the engine temperature sensor; intake air temperature sensor, air flow meter signal or oxygen sensor, the DME control unit makes available suitable substitute values. These substitute values are cancelled once again as soon as normal operation can be resumed. For further information, refer to notes on BMW DIAGNOSTIC SYSTEM.

Notes on the BMW DIAGNOSTIC SYSTEM

Control Unit Assignment
Initially, the identification data are displayed in order to determine whether the correct control unit is installed. The assignment can be determined by means of the version code (e.g. C01E) and parts microfilm without having to remove the control unit.

Explanation of Control Unit Identification
The designation of the DME version and the indication as to with which row of cylinders communication is currently established appear in the first line.

Further data are displayed in the following sequence
- Version: model designation, engine type
- With or without oxygen control
- Transmission version:
HG - Manual transmission
AG - Automatic transmission, hydraulic
EH - Automatic transmission, electronic-hydraulic
- Type of fuel: Leaded/unleaded or regular/premium
- Country version: International identification
- Control unit version code: Available from BMW Parts Catalog.
- BMW hardware and software number
- Bosch hardware and software number
- Production code: Used only on special request by Service Division.

Monitoring Defect Code Memory - [D] 900
Defect code memory monitoring should be given first priority. If one or several defect codes are stored, it is advisable to immediately print out these data (R button). Since it is often necessary during the testing procedure to cut the power supply or to disconnect the connector from the control unit, the content of the defect code memory will be unintentionally deleted as a consequence.

Model '87/'88: The memory can store a maximum of 5 defect codes, whereby a defect code with higher priority can displace another defect code from the memory. The defect codes are displayed in the order of detection.

The following defects have higher storage priority:
- air flow meter,
- oxygen control,
- engine temperature sensor and
- idle switch

As of model '89: The extended defect code memory stores all defect codes which are detected. When a defect code is stored and the DME is not malfunctioning, substitute values can be active. The troubleshooting procedure should still, however, be carried out.

In US models, defect codes which influence the mixture are indicated by a lamp (engine check) in the instrument duster. As a check, this lamp lights constantly in the time between "Ignition ON" and engine start.

Clearing the Defect Code Memory - [D] 999
This step should be carried out when the defect has been repaired or was caused by simulation. When the battery or the OME control unit are disconnected, all stored defect codes as well as the substitute values are lost. Current detect codes cannot be cleared.

Status Monitoring [D] 100 and [D] 200
Further information can be called independent of defect code storage. Current values or current operating statuses are displayed in this way. Refer to the chapter - Component Testing for the necessary comparison of set values.

Component Activation - [D] 300
To facilitate fast faultfinding, various components can be activated with the DME control unit together with the service tester. This makes it possible to distinguish between faults in the control unit the supply line or in the component itself. Detailed information on this simulation mode is displayed on the screen.

Abbreviations
ABS Antilock brake system
AG Automatic transmission
ASC Automatic stability control
DK Throttle valve
DWA Antitheft system
EKP Electric fuel pump
EML Electronic throttle control
EV Injector valve
HG Manual transmission
HLM Air flow meter heating filament
KD Kickdown
KW Crankshaft
LL Idle
MF Microfilm
MSR Engine drag torque control
MV Solenoid valve
PWG Pedal value sensor
RxD Diagnosis initiation line
SG Control unit
TE Fuel evaporation control
TD Engine speed signal once per Ignition
TR Crankshaft reference once per revolution
ti Injection timing
tL Load signal
VL Full load
TL Partial load
TxD Diagnostic data line
U-Batt Battery voltage
U-Vers Voltage supply