An intake manifold flap is located in the air intake system which has the following functions:
โข Restricting the intake air for exhaust gas recirculation,
โข Closing the intake system when the engine is stopped,
โข Closing the air path via the intercooler while the regeneration of the diesel particulate filter takes place
The intake manifold flap is actuated by a servo motor. The servo motor is a DC motor that precisely controls the requested position of the intake manifold flap through actuation by the PCM.
In addition, there is a position sensor in the servo motor that informs the PCM of the current position of the intake manifold flap (closed control loop).
In order to restrict the intake air flow, the intake manifold flap is closed by a set percentage value depending on requirements.
This produces a specific vacuum behind the intake manifold flap. This vacuum results in the recirculated exhaust gases being drawn in more efficiently by the engine via the EGR valve and therefore in a higher EGR rate to be delivered to the cylinders.
1 Power supply from the battery junction box
2 PCM
3 DC motor
4 Servo motor
5 Position sensor
When the engine is stopped, the intake manifold flap is closed. This prevents intake air from being drawn in and, consequently, running on (judder) of the engine.
In the case of vehicles with a diesel particulate filter the intake air temperature has to be increased under certain operating conditions for the regeneration process.
To achieve this, the intake air valve is closed depending on requirements and an intercooler bypass opened (bypass of the intercooler).
Effects of faults
The intake manifold flap is sticking in the open position:
โข EGR is limited or switched off.
โข When switching off the engine, increased engine judder occurs.
The intake manifold flap is sticking in the closed position:
โข Engine does not start.
If the intake manifold flap is sticking, only limited control of exhaust gas recirculation is possible.
Depending on the position in which it is sticking, too much exhaust gas could be recirculated under certain load conditions. In this case, the injected fuel quantity and therefore the engine power output is reduced to prevent black smoke.
Serious faults at the position sensor will result in the EGR system being deactivated.
Diagnosis
Monitoring the intake manifold flap (by means of the position sensor) includes the following checks:
โข Limit range check,
โข Plausibility check,
โข Control deviations,
โข Sticking intake manifold flap.
Most faults result in limited exhaust gas recirculation or the EGR system being deactivated, which means that the maximum exhaust emission levels are exceeded. Therefore this is a MIL active component.
Possible diagnostic trouble codes: P0407, P0408, P0487, P0488, P2141, P2142.