Location
A4 | Engine management control unit (MCM) |
W07.08-1015-82
The engine management (MCM) control unit (A4) is located on the left side of crankcase.
Task
The engine management (MCM) control unit (A4) services primarily as an interface between the electrical or electronic components located on the engine side and drive control (CPC) control unit (A3) on the vehicle side. Both Control units are networked together via the drive train CAN (CAN 4) and the CAN bus drive neutral point (Z4). The engine management (MCM) control unit (A4) takes on a number of tasks. On the one hand it takes on the controlling and regulating processes, for example for systems such as the engine management or the exhaust gas recirculation (EGR) while, on the other hand, it serves to pass on information such as the oil level in the engine.
Below you will find an overview of the tasks of the engine management control unit (MCM) (A4):
Engine management for the common rail diesel injection system
The main task of the engine management control unit (MCM) (A4) is to control the injection of the common rail diesel injection system. All required data such as the output, diverse performance maps or data which serves to protect the engine is stored in the engine management (MCM) control unit (A4). To regulate the injection which takes place through appropriate actuation of the fuel injectors for cylinder 1 to 6 (Y608 to Y613), the pressure regulating valve (Y634) and the quantity control valve (Y643), the engine management (MCM) control unit (A4) reads in signals from virtually all sensors connected to it. This means: all information except that from the oil pressure switch (B604) and the engine oil fill level sensor (B605), are included in the computations.
Exhaust gas recirculation (EGR)
The fact that exhaust gas recirculation is active over the whole rotational speed range means that the ratio between recycled exhaust gas masses and suctioned in or supercharged fresh air mass must be matched exactly and thus exactly regulated. This relationship, the so-called exhaust gas recirculation rate, is regulated by the engine management (MCM) control unit (A4) through appropriate actuation of the exhaust gas recirculation positioner (Y621). The EGR rate value here is determined by the information from the charge air pressure and temperature sensor (B616), by the oxygen sensor (B624) and by the charge air temperature sensor in the charge air housing (B617), taking the data stored in a corresponding characteristics map into account.
Diesel particulate filter (DPF) - only for code M5Z (Engine version Euro VI)
During the active regeneration phase of the diesel particulate filter (DPF) the engine management (MCM) control unit (A4) actuates the fuel shutoff valve (Y629) and (in intervals) the fuel metering valve (Y628). The fuel shutoff valve (Y629) and the fuel metering valve (Y628) are located together with the fuel pressure sensor (outlet) (B625) and the fuel pressure sensor (inlet) (B626), in one metering device. This ensures that diesel fuel is metered over a line to the injection nozzle in the nozzle unit for DPF regeneration which is located on the exhaust pipe upstream of the diesel particulate filter (DPF). The injection nozzle injects specific fuel amounts into the hot exhaust flow. During the resulting reaction in the exhaust aftertreatment unit, a great deal of heat is generated, in which the soot deposited in the diesel particulate filter (DPF) is burnt to form ash.
Charge pressure control
The engine management (MCM) control unit (A4) determines the current boost pressure with the aid of the charge air pressure and temperature sensor (B616). It the boost pressure is too high, it transmits an appropriate message to the boost pressure regulator (Y636), which is actuates the boost pressure control flap over a linkage.
Instrument cluster
To display this in the IC the engine management (MCM) control unit (A4) detects the engine oil level, the engine oil temperature, the engine oil pressure, the coolant temperature and the engine rpm. It also uses values from the following sensors:
Engine oil fill level sensor (B605)
Oil pressure switch (B604)
Exhaust coolant temperature sensor (B606)
Crankshaft position sensor (B600)
Fan control
For fan regulation the engine management (MCM) control unit (A4) uses information from the coolant outlet temperature sensor (B606) and the fan rpm sensor (Y616 b1). It evaluates this information then actuates the fan clutch solenoid valve (Y616) over a characteristics map.
Engine brake
On request from the drive control (CPC) control unit (A3) the engine management (MCM) control unit (A4) actuates the engine brake solenoid valve (Y637). Actuation of the solenoid valve means that the engine oil is led to the hydraulic engine brake units, whereby the engine brake is active.
Camshaft adjustment
For engine rpms at lower exhaust temperatures the camshaft positioner should be driven in the position "advanced" in order to increase the exhaust temperatures. This is the prerequisite for later active purging of the diesel particulate filter. The adjustment takes place through appropriate actuation of the camshaft positioner solenoid (Y635), dependent on the exhaust temperature and the engine rpm.
Tasks covering a number of systems
These tasks include engine or system diagnosis, since almost all electrical or electronic components which are attached to the engine management (MCM) control unit (A4) can be diagnosed.