The Siemens engine management system MS 41 supersedes the MS40 for the M52.
The crankshaft sender is an active sender which operates on the Hall sender principle. An evaluable signal is transmitted by the sensors from about 20 rpm. The sender is supplied with a constant voltage of 5 V from the DME control unit.
This engine concept utilizes a stereo Lambda control. The Lambda probes (resistance difference probes) are located in the exaust manifold. This location allows the dead times for the individual exhaust paths to be reduced and more precisely monitored. Each probe monitors three cylinders (cylinders 1-3 and 4-6). Test example: If the injector opening time of the first line of cylinders (cylinders 1-3) is changed, a reaction should be observed on the Lambda probe of the first line. If this is not the case, renew the probes.
The MS 41 has a double temperature sensor for the DME control unit and the remote thermometer in the instrument cluster. The temperature sensor converts the temperature of the engine coolant into an electrical value (resistance). This is done using an NTC. A coded connector makes it impossible to attach the incorrect connector at the wiring harness.
The knock sensors detect a knocking combustion and work in accordance with the familiar operating principle of the Pizzero sensor. One knock sensor monitors cylinders 1-3, another monitors cylinders 4-6. They are only linked at the connector, or at the wiring harness, and transmit separate signals to the DME control unit.
Thanks to a modified physical construction, the ignition coils have been made smaller and lighter (300g instead of 400g). The MS41 and MS40 ignition coils cannot be interchanged.
The control unit is a single plate unit with an 88-pin connector. There is only one control unit version for each engine displacement. The difference between manual and automatic transmission, or between catalyst and catalyst preparation is learned by the control unit. The learned version can be reset using DIS or MoDiC ("Diagnosis" "Service Functions" "Delete Adaptions")
The control unit has a permanent data memory (EEPROM). Here, the adaptions and contents of the fault memory are stored in a non-volatile form. These entries can only be deleted using DIS / MoDiC. They are not deleted by disconnecting the battery. The adaptions must be deleted if the control unit from another vehicle is installed (test exchange).
The serial data transmission is made bi-directionally via a two-wire, twisted lead between the DME and EGS control units.
The following data are transmitted from the DME to the EGS:
- Terminal 15 status
- Air conditioner compressor actuation
- Torque reduction via ignition
- Load signal with fault recognition (load signal with substitute value)
- Engine speed
- Coolant temperature
- Intake air temperature
- Road speed
- Throttle valve angle
The following data are transmitted from the EGS to the DME:
- Gear shift target gear
- Gear shift status ACTIVE
- Converter coupling switch open or closed
- Position selector lever
- OBD status of transmission management
- Torque reduction target from transmission management
- Program information
- Output speed
- Emergency running programm in EGS
The speed signal comes directly from the ABS/ASC control unit. All wheel speed signals are processed in the ABS control unit and output in the form of a square wave signal.
The ASC/MSR inputs correspond to the Bosch DME. The ASC functions within the MS41 are executed by evaluating the logical statuses at the ASC interface.
Since 01/95, every vehicle is equipped as standard with a coded vehicle immobilization system. A coded data transfer takes place between the EWS and DME control units. See also EWS functional description.
The tank bleed valve serves a managed regeneration of activated carbon filter (AKF) using scavanging air. The scavanging air drawn through the activated carbon filter is enriched with hydrocarbons (HC) according to the level of charge of the activated carbon (HC) and then fed into the engine for combustion.
The development of hydro-carbons from the fuel tank is highly dependent on:
- the fuel and ambient temperatures
- air pressure
- the fuel level within the tank
The tank bleed valve is closed when in a flow-free state. This prevents fuel vapours from the AKF reaching the intake manifold when the engine is not running.
A single-wire diagnostic interface has been introduced to meet the demands of the new diagnostic concept (similar to E38 / E39). The complete data transfer runs bi-directionally. One wire could therefore be eliminated.
A flap-controlled silencer system is installed on various M52 versions to reduce exhaust noise. To realise an active silencer syste, the exhaust system was given a controlled electro-pneumatic exhaust flap at the tail pipe of the main silencer. The DME control unit actuates an electronic switch-over valve which supplies a depression to a vacuum capsule. If the DME control unit requires the exhaust flap to be closed, it outputs an "ground" signal. The switch-over valve is actuated and the exhaust flap closed.
Under "running losses", one understands the separation or evaporation of fuel, oil, washer water, underfloor protection or engine fumes. In the USA, lawmakers demand a strict examination of vehicles in this respect. Carmaker must therefore construct and fit all fluid containers, pipes etc. in such a way that no vapours can escape.
The new 3/2-way valve reduces the heating up of the fuel and therefore the evaporation of the fuel. By using the 3/2-way valve, two fuel circuits, one smaller and one larger were created. The large fuel circuit is required in the start-up phase. In this phase, the fuel injection strip is washed with the entire quantity of fuel supplied (possible vapor bubbles washed out). When the engine has been running for approximately 20 seconds, the valve is de-activated, allowing the small circuit to be utilised.
Regardles of the pollutants created by the combustion within the engine, a vehicle will emit considerable amounts of unburned hydro-carbons. These hydro-carbon emissions can stem from leaks in the fuel system, but also from an insufficiently large tank bleed system (activated carbon filter becomes permeable).
For this reason, a further OBD II requirement refers specifically to the fuel system and the fuel tank bleed system. The maximum permissible level of escaping fuel fumes has been determined anew. Moreover, leaks larger than 1 mm in the fuel system must be recognised by the DME.
To this end, the following measures have been implemented in BMW vehicles:
- Fuel temperature reduced through new fuel circuit with 3/2-way valve
- The activated carbon filter has been reshaped
- New activated carbons with improved absorption capability
- Inclusion of a tank bleed system diagnosis with the DME, using an AKF cut-off valve and a fuel tank pressure sensor
The tank bleed system diagnosis i sperformaed automatically in pre-defined cycles. It is only performed with the engine running. In order that leaks in the fuel tank and the tank bleed system be detected, the entire system must be sealed air-tight. This is done by the cut-off valve (AAV) on the activated carbon filter (AKF).
Depression sytem:
The fuel tank bleed valve (TEV) is opened. This remains open until a depression of 5-10 mbar in the entire system has been generated by the intake system. The depression in the fuel tank system is measured by the fuel tank pressure sensor.
The fuel tank bleed valve is closed when the required depression is attained.
Now, the fuel tank bleed valve and the AKF cut-off valve are both closed together. In this state, the DME control unit uses the fuel tank pressure sensor to monitor the previously generated depression in the fuel tank and fuel tank bleed system. If the depression drops below a given threshold within about 10 seconds, the DME will recognize a leak.
Pressure release system:
The LDP (leak detection pump) is switched on, the fuel tank bleed valve closed. The LDP remains on until a pressure of 5-10 mbar in the entire system has been generated. The pressure in the tank is measured by the reed switch in the LDP.
The LDP is switched off when the required pressure has been reached.
Now, the fuel tank bleed valve and the AKF cut-off valve are closed together, the LDP is switched off. In this state, the DME control unit uses the fuel tank pressure sensor to monitor the previously generated pressure in the fuel tank and fuel tank bleed system. If the pressure drops below a given threshold within about 10 seconds, the DME will recognize a leak.
A second Lambda probe (the monitor probe), installed behind the catalytic converter, monitors the problem-free operation of the catalyst. To recognize the functional ability of the cytalytic converter, the DME control unit compares the signals from the control probe (before the catalyst) and the monitor proble (after the catalyst).
the operation of the control Lambda probe is similarly monitored. Incorrect Lambda probe operation, caused for example by the use of leaded gasoline, causes a change in the Lambda control frequency, which is recognised as a fault by the DME control unit.
An inductive impulse sender on the increment gear to measure the speed of rotation (rpm) of the engine. Moreover, the smooth running of the engine is also monitored (misfire detection) as a measure of the engine speed.
To detect misfires, the increment gear is divided (by the control unit) into 3 segments according to the ignition separation (e.g. 3 sparks per crankshaft turn on a 6-cylinder engine). Within the control unit, the periodic duration of the individual increment gear segments is measdured and statistically evaluated. For each point on the characteristic map, the maximum permissible rough running values are stored as a function of engine speed, load and engine temperature.
If these values are exceeded, the cylinder registered as faulty is stored in the fault memory.
The diagnosis program offers a test step, "smooth running measurement". Here, the smooth running values of the individual cylinders are indicated in a bar chart.
OBD II demands that the operation of the secondary air system be monitored. To do this, the operation of the secondary air injection and of the cut-off and air switch-over valves are monitored each time they are activated. The secondary air injection serves as an exhaust gas aftertreatment during the engine warm-up phase. Here, fresh air is blown directly into the exhaust manifold.
About 10 seconds after the engine is started, the secondary air pump is activated by the SLP relay. The time until it is switched on is dependent on the following fringe conditions:
- Engine temperature
- Load signal
- Engine speed
During the activation of the secondary air pump, the Lambda probe voltage is monitored in the DME control unit. During problem-free operation of the secondary air system, the Lambda probe voltage is primarily in the lean range.
At regular intervals (every 20ms), the Lambda probe voltage is registered within the control unit. Each measurement in which the Lambda probe voltage is registered as being in the lean range is counted by an internal counter. If this count exceeds a pre-defined threshold, the system is recognised as being fully operational. If this threshold is not reached, the DME recognises a fault within the secondary air system. An entry is made in the fault memory.
As has been commonplace on BMW vehicles for some years now, almost all electrical and electronic components of the engine management system are monitored by the DME control unit. In the event of electrical, or in some cases even mechanical malfunctions occuring, these are recognised and stored in the DME fault memory.
In the event of malfunctions occuring in components whose failure or incorrect operation would affect the exhaust gas composition, the "CHECK ENGINE" warning lamp lights up in the instrument cluster in addition to the entry being made in the fault memory.