V50 T5 AWD L5-2.5L Turbo VIN 67 B5254T7 (2008)
return position gives a throttle angle large enough to allow the car to be driven to a workshop, although with considerably reduced drivability.
Throttle angle
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 stored. 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
Normally the engine control module (ECM) adapts the throttle unit during manufacture of the car. There are a number of other occasions when the
throttle unit must be adapted. A new adaptation is obviously required if the throttle unit or the engine control module (ECM) is replaced, but also if the
software in the engine control module (ECM) is replaced. This is because the adaptation values are stored in the EEPROM memory in the control
module, at a predetermined location in the memory for each software. These storage locations may vary between different software, in which case a new
adaptation will be required. The final reason for adaptation is that the values for the throttle unit may have changed during its service life. Therefore
there is a routine which begins adaptation of the throttle unit if the car is left with the engine off and the ignition on for 30 seconds (and other basic
conditions for adaptation of the throttle unit are met). A new adaptation is then carried out. If the "new" values are different from the "old" values, the
new values are used. Adaptation usually takes place automatically when the engine control module (ECM) detects that the adaptation has not been run or
that the values from a previous adaptation are outside certain tolerances. However a number of basic conditions must be met to ensure that the adaptation
is carried out correctly.
Basic conditions for adaptation of the throttle unit:
-
ignition on/engine off
-
battery voltage above 10 V
-
accelerator pedal (AP) released (unaffected)
-
the car must be stationary (no speed signal)
-
engine coolant temperature (ECT) between 5 and 100 degree C
-
intake air temperature (IAT) above 5 degree C.
During adaptation, the engine control module (ECM) checks that the values obtained are within reasonable limits. This helps to determine whether the
throttle unit is functioning correctly or not. When the adaptation has been carried out, all relevant values are stored in the EEPROM memory in the
control module so that they can be retrieved if the power supply is broken. This means that if the battery is replaced for example, a new adaptation is not
necessary.
