The throttle angle is usually gauged by potentiometer 1. For small angles the amplified signal is used to obtain a clearer signal. The engine control
module (ECM) also monitors the throttle unit signals from the potentiometers to check that they are plausible, that they are within the minimum and
maximum limits and that the signals correspond to the same throttle angle. If there is a difference in the signals, a fictitious throttle signal is calculated
from the load signal, the engine speed (rpm) and the prevailing conditions, particularly pressure and temperature.
The potentiometer whose signal is closest to the calculated throttle angle will then be assumed to be correct. The other potentiometer is then classified as
not functioning and a diagnostic trouble code (DTC) is generated. The system then constantly monitors the throttle angle of the remaining potentiometer
in comparison to the calculated throttle angle. If there is a difference between these values, the engine control module (ECM) will not rely on any of the
throttle unit potentiometers. The power stage in the throttle unit is then disengaged, and the throttle switches to limp home mode.
Adaptation of the throttle unit
In ignition position II, the engine control module (ECM) carries out adaptation of the electronic throttle unit. Adaptation is carried out by the throttle disc
being mechanically controlled to the closed position and the current throttle position being read off. If previous adaptation values are missing in the
engine control module (ECM), for example, if the control module has not been powered, the current throttle angle is stored as the adaptation value. If, in
addition, there is a previously stored value, the average value of the previous one and the current throttle angle is stored as the new adaptation value.
Hint: When replacing the electronic throttle unit, the engine control module (ECM) must therefore always be switched off.