1 Air flow in intake manifold
2 Intake manifold flap
3 PCM
4 Intake manifold flap solenoid valve
5 Vacuum unit
In some versions, a vacuum-operated intake manifold flap is used, which is actuated via an intake manifold flap solenoid valve.
The intake manifold flap has the following functions:
โข Preventing “serious engine judder” when the engine is stopped,
โข Closing the air channel through the intercooler (vehicles with fuel additive diesel particulate filter),
โข Restricting the intake air to improve the EGR rate (certain vehicles with emission standard IV).
โข Restricting the intake air to assist the increase in
exhaust gas temperature during the active regeneration process (vehicles with coated diesel particulate filter).
Preventing “serious engine judder” when the engine is stopped:
โข Diesel engines have a high compression ratio. The high compression pressure of the intake air affects the crankshaft via the pistons and connecting rods and causes judder when the engine is stopped.
โข The intake manifold flap solenoid valve connects the vacuum for the intake manifold flap vacuum unit, as a result of which the intake manifold flap is closed. This prevents engine judder when the engine is stopped.
โข The intake manifold flap solenoid valve is energized when the engine is stopped. The vacuum for actuation of the intake manifold flap vacuum unit is activated and the intake manifold flap is closed briefly.
Closing the air channel through the intercooler (vehicles with fuel additive diesel particulate filter):
โข This function is utilized when the exhaust gas temperatures are low in vehicles with diesel particulate filters. The intake manifold flap closes the air channel through the intercooler at the same time as the intercooler bypass is opened (see relevant section in this brochure).
An additional function in other versions is that the air intake is restricted for better exhaust recirculation at low engine speeds.
Restricting the intake air to improve the EGR rate (certain vehicles with emission standard IV)
With certain vehicles, the normal exhaust gas recirculation is not adequate to return the required EGR rate. By slightly restricting the intake air using an intake manifold flap, a vacuum is created in the intake tract. This vacuum increases the EGR flow.
Effects of faults
In the event of a signal failure or a failure of the intake manifold flap solenoid valve:
โข the intake manifold flap remains open when the engine is stopped. This results in increased engine judder when the engine is stopped.
โข controlled Exhaust Gas Recirculation is only possible to a limited extent.
โข the regeneration of the diesel particulate filter cannot be performed in an ideal way under certain conditions.
Diagnosis
The intake manifold flap solenoid valve is checked for short circuit and open circuit in the context of EOBD.
Faults can be classified as either MIL active or non MIL active (depending on the function of the component in the strategy).