Function [4 of 4]

Adaptive functions




Certain factors, such as deviations in tolerance for certain components such as the mass air flow (MAF) sensor and injectors, intake air leakage, fuel pressure etc, will affect the composition of the fuel air mixture. To compensate for this, the engine control module (ECM) has adaptive (self learning) functions. When the engine is new, the short-term fuel trim is assumed to vary cyclically around a nominal center line (A) 1.00 with, for example, a ± 5% change in the injection period when fuel trim is active.
If there is air leakage for example, the short-term fuel trim will quickly be offset to a new position (B) and will then work for example between 1.10 (+10%) and 1.20 (+20%), although still at an amplitude of 5%, but with an offset in relation to the original center line (A). The injection period has then been increased to compensate the increase in the amount of air.
The adaptive functions will correct the change, so that the short-term fuel trim will work around the new center line (B) where it will again have its full range of control available.
Put simply, fuel trim is a measurement of the difference (C) between the original short-term fuel trim center line (A) and the new center line (B).




The adaptive functions consist of two sections and correspond to the different operating ranges of the engine, load (D) and engine speed (E):
- Additive adaptation (1) is when the engine is idling. This is how the control module adjusts the CO content at idle speed. Long-term fuel trim, idling can be read off using VIDA.
- Multiplicative adaptation (2), carried out at loads and engine speeds above idle. Long-term fuel trim, load can be read off using VIDA.
The adaptive adjustments of the injection period are stored continuously in the control module. This means that under different operating conditions the fuel air mixture is obtained before the heated oxygen sensor (HO2S) is warm enough to function.
A diagnostic trouble code (DTC) will be stored in the control module if any adaptation value is too high or too low. For further information, also see: Heated oxygen sensor (HO2S) diagnostic Description and Operation

Knock control




Knock occurs in the combustion chamber when the fuel and air mixture self ignites. This can occur either before or after the spark plug has produced an ignition spark. In both cases the gas in two or more places ignites in the combustion chamber.
This results in an extremely fast combustion process with flames from several directions. When these flames collide, the pressure in the cylinder increases rapidly and there is a mechanical knocking sound.
If any of the cylinders knock there is a specific type of vibration in the cylinder block. These vibrations are transferred to the knock sensors (KS) which are screwed into place in the cylinder block. The resultant mechanical stress in the piezo electrical material in the knock sensors generates a voltage. The engine control module (ECM) can then determine which cylinder is knocking with the help of the camshaft position (CMP) sensor and the engine speed (RPM) sensor.
The knock sensors (KS) also interpret a proportion of normal engine sound. The control module is able to recognize the vibrations which correspond to knocking by filtering, amplifying and using software to evaluate the signal.
If the knock sensors (KS) detect knocking in the engine above a certain threshold value, the ignition timing is first retarded and then the fuel/air mixture is enriched to eliminate knocking.

Ignition control




The following components are used for ignition control:
- engine speed (RPM) sensor (7/25)
- camshaft position (CMP) sensor (7/172-7/173)
- mass air flow (MAF) sensor (7/17)
- engine coolant temperature (ECT) sensor (7/16)
- throttle position (TP) sensor on the electronic throttle unit (6/120)
- knock sensor (KS) (7/23-7/24)
- transmission control module (TCM) (4/28)
- spark plugs with ignition coils (20/3-20/7)
- brake control module (BCM) (4/16).
The engine control module (ECM) calculates the optimum ignition advance based on the software and information from the sensors. The engine control module (ECM) cuts the current to the ignition coil mounted on the cylinder to be ignited and produces a spark.
During the starting phase the engine control module (ECM) produces a fixed ignition setting. When the engine has started and the vehicle is being driven, the engine control module (ECM) calculates the optimum ignition setting, taking factors such as the following into account:
- engine speed (RPM)
- load
- temperature.
The engine control module (ECM) analyses the signal from the knock sensors (KS) when the engine reaches operating temperature. If any of the cylinders knock, the ignition is retarded for that specific cylinder until the knocking ceases.
The ignition then advanced to the normal position or until the knock recurs.
Before the transmission control module (TCM) changes gear, it sometimes transmits a torque limiting request to the engine control module (ECM). The engine control module (ECM) then retards the ignition momentarily to reduce the torque, resulting in smoother gear changes and reducing the load on the transmission. There are different ignition retardation levels depending on the signals from the transmission control module (TCM). The return signal from the engine control module (ECM) to the transmission control module (TCM) confirms that the signal reached the engine control module (ECM). The Brake Control Module (BCM) transmits information to the engine control module (ECM) about deviations in the drive line. The signal is used to stop the diagnosis. For further information, also see: Misfire diagnostic Misfire Diagnostics
The engine misfires if the fuel does not ignite correctly. For further information, also see: Misfire diagnostic Misfire Diagnostics

Regulating the air conditioning (A/C) compressor




The air conditioning (A/C) compressor is controlled by the engine control module (ECM) (4/46) on request from the climate control module (CCM) (3/112) via the controller area network (CAN). When the engine control module (ECM) receives a signal from the climate control module (CCM) to activate the air conditioning (A/C) compressor, the engine control module (ECM) grounds the circuit for the relay coil for the A/C compressor. See also: Design Design
The relay (2/22) closes the circuit between the integrated relay/fusebox in the engine compartment and the clutch for the A/C compressor (8/3).
In addition to the information from the climate control module (CCM), the engine control module (ECM) checks the engagement and disengagement of the A/C compressor based on:
- the signal from the air conditioning (A/C) pressure sensor (high pressure side) (7/8)
- the signal from the air conditioning (A/C) pressure sensor (low pressure side) (8/119)
- the throttle position (TP) sensor (6/120)
- the engine coolant temperature (ECT) sensor (7/16).

Regulating the cruise control




The cruise control function is an example of distributed functionality.
The following components are used when regulating the cruise control:
- engine control module (ECM) (4/46)
- steering wheel module (SWM) (3/254) (cruise control buttons)
- central electronic module (CEM) (4/56) (clutch pedal position)
- brake control module (BCM) (4/16) (brake pedal position, speed signal)
- driver information module (DIM) (5/1) (cruise control lamp)
- transmission control module (TCM) (4/28) (cruise control active/not active, gear selector in position "P" or "N")
- electronic throttle unit (6/120)
- stop lamp switch (3/9)
To activate cruise control the function must be switched on using the "CRUISE" button. A lamp lights up in the driver information module (DIM).
The driver activates the function by pressing the SET+ or SET- button. A message is then transmitted via the low speed side of the CAN network to the central electronic module (CEM) which then transmits the message on via the high speed side of the CAN network to the engine control module (ECM).
The engine control module (ECM) controls the throttle angle so that a constant speed is maintained using the vehicle speed signal from the Brake Control Module (BCM). The transmission control module (TCM) also receives a message indicating that cruise control is active via the Controller area network (CAN), so that the transmission follows certain shifting patterns when the cruise control is active.
If the accelerator pedal (AP) is depressed the speed increases as normal and then resumes to the stored value when the driver releases the accelerator pedal (AP) again.
The engine control module (ECM) continually stores the speed. If cruise control is disengaged, for example by the driver pressing the brake pedal, the previous stored speed can be used by pressing the "RESUME" button.
Cruise control cannot be activated at speeds below 30 km/h.
Cruise control is disengaged:
- when the driver presses the clutch pedal or brake pedal
- when the driver presses the "CRUISE" button on the steering wheel
- when the driver depresses the "0" button on the steering wheel
- if "P" or "N" positions are transmitted on the Controller area network (CAN) (applies to automatic transmissions)
- if the speed deviates too much from the set value
- when certain diagnostic trouble codes (DTCs) are stored which do not allow continued activation (For further information see diagnostic trouble code (DTC) information).

Regulating the alternator (2005-)




The engine control module (ECM) (4/46) regulates the alternator charging voltage (via LIN communication) in response to a request from the central electronic module (CEM) (4/56) (via CAN communication).
The engine control module (ECM) can change the requested charging voltage from the central electronic module (CEM) in order to adapt it to certain operating conditions such as starting, idling or high engine loads.
The value requested by the engine control module (ECM) for charging voltage and alternator charging current can be read using VIDA.
The alternator control module (ACM) sends fault information to the engine control module (ECM). Diagnostic trouble codes are stored in the engine control module (ECM).
For additional information on regulating the alternator, see Design and Function, Alternator and Design and Function, central electronic module (CEM).