1 Intake manifold
2 Intake manifold flap
3 Intake manifold flap solenoid valve
4 Vacuum unit
5 PCM
6 Ignition lock
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.
The intake manifold flap solenoid valve connects the vacuum for the vacuum unit of the intake manifold flap in the intake manifold, as a result of which the intake manifold flap is closed. This prevents engine judder when the engine is stopped.
The intake manifold flap solenoid valve is energized when the engine is stopped. As a result, the vacuum to the vacuum unit for actuating the intake manifold flap is released and the intake manifold flap is closed briefly as a result.
If the signal fails, or if the intake manifold flap solenoid valve fails, the intake manifold flap remains open when the engine is stopped.
Effects of faults
Intake manifold flap jams open:
โข Starting and engine running are not adversely affected.
โข However, when the engine is stopped, it judders severely.
Intake manifold flap jams closed:
โข Engine does not start.
Diagnosis
The monitoring system checks:
โข the relevant solenoid valve for short circuit and open circuit.