Function
A high temperature (approx. 600 ยฐC) is needed to burn off the diesel particulates trapped in the diesel particulate filter. This temperature, however, is not attained in all of the engine’s operating conditions.
In the lower part load range, the intake manifold flap is partly closed and thus assists in increasing the temperature.
The intake manifold flap is closed by the intake manifold flap solenoid valve via a vacuum.
Effects in the event of a faulty solenoid valve
Malfunctions usually result in the intake manifold flap being moved into the fully open position by the return spring.
With frequent journeys in the lower part load range, a non-closing” of the intake manifold flap may mean that the active regeneration process cannot be carried out as calculated.
The strategy of the PCM tries to balance out the malfunctions of the intake manifold flap by increasing the injected fuel quantity in the post-injection. However, this results in the fuel rapidly diluting the engine oil.
Diagnosis of the solenoid valve
The monitoring system checks:
โข the relevant solenoid valve for short circuit and open circuit.