Adaptations and Equipment Variations

Adaptations And Equipment Variations

The adaptation makes it possible that the engine control unit can learn certain values of components and thus compensate for certain component tolerances.

When used for the first time, the engine management system also learns equipment variations that are fitted.

The service function "Reset adaptation values" can be used to reset the adaptation values and equipment variations to their default settings; thereafter, they have to be relearned. Longer operation between idle speed and partial load is necessary, for example, in order to learn the mixture adaptation values.
- Deleting adaptations after repairs:
in general, the adaptations should not be deleted after a repair (part replacement). On replacement of the throttle valve, the MDK adaptations are to be deleted to avoid a diagnostic fault code memory entry.
- Deleting equipment variations and adaptations after a conversion or vehicle upgrades:
after a vehicle conversion, e.g. from manual to automatic transmission, or vehicle upgrade, e.g. retrofitting a trailer module or a multifunction steering wheel, the equipment variations and adaptations must be deleted and relearned.

Examples of various adaptations

Fuel mixture adaptation
The mixture formed in the intake area requires some time before it reaches the oxygen sensor as exhaust emissions. This time decreases as load and engine speed increase. For this reason, the response time of the emission (Lambda) control system is also dependent on load and engine speed. Fuel-air mixture deviations detected by the oxygen sensor result in adaptation values (learned correction values) being stored. By way of the adaptations, the injection can be brought close to the nominal value in advance. A reduction in the response time is achieved in this way.

For example, if the basic fuel injection values of the engine control unit characteristic map are too low at idle speed to maintain the ideal fuel-air mixture, the oxygen-sensor control would have to continuously increase the fuel injection period. In this case, an adaptation value is learnt which corrects the basic injection value. The emission (Lambda) control then only needs to undertake the fine adjustment.

Idle mixture adaptation (additive)
If idling is detected in the off-load phase of the tank ventilation due to the throttle-valve position, an idling fuel mixture adaptation is made at certain intervals. As the idling and part-load fuel mixture adaptations mutually influence one another, complete adaptation requires a number of switches between idling and part-load.

Partial load mixture adaptation (multiplicative)
Also in the part-load range, a fuel mixture adaptation is carried out at regular intervals. The determined adaptation value is taken into consideration in all partial load ranges.

Tank venting adaptation
When the tank ventilation valve is open, an additional combustible mixture is supplied from the carbon canister to the engine. The shift in mixture detected by the oxygen sensor is completely corrected out by means of the tank ventilation adaptation value.

Idle speed adaptation
The idle speed adaptation is handled by the idle actuator. It uses the air volume to ensure a constant idle speed.

Sensor adaptation
Misfiring causes irregularities in the rotational speed of the crankshaft. These irregularities can be detected by way if changes in the segment time.

The crankshaft sensor continuously determines segment times (time in which a certain number of teeth of the increment gear run past the sensor). These segment times are constantly checked during engine operation. In the event of a fault, a corresponding fault code is stored in the fault code memory and the fuel injection is deactivated at the corresponding cylinder. Refer to misfiring detection.

To prevent incorrect evaluations, a sensor adaptation must be run after replacement of the DME control module or crankshaft sensor.

If the increment gear is replaced, the sensor adaptation must be deleted both before and after replacement.

The sensor wheel adaptation determines the irregularity of the increment wheel and takes it into consideration when evaluating the segment times. The sensor adaptation is run automatically as soon as the engine is overrun for at least 10 seconds.