During the regeneration phase, the intercooler bypass flap opens, enabling uncooled charge air to be directed to the combustion chambers.
The uncooled air prevents cooling of the combustion chamber when engine speeds/engine loads are low and this promotes the regeneration of the diesel particulate filter.
The intercooler bypass flap servo motor incorporates a DC motor and a position sensor which detects the current position of the intake manifold flap.
1 PCM
2 Servo motor
3 Position sensor
4 DC motor
The DC motor is supplied with battery voltage by means of the ignition relay in the battery junction box. The actuation of the DC motor and therefore the adjustment of the intercooler bypass flap is performed by the PCM connecting to ground (pulse width modulated).
The position sensor is supplied with a reference voltage. The voltage drop across the position sensor (variable resistance via sliding contact) signals the precise angular position of the intercooler bypass flap to the PCM.
Effects of faults
In the event of a fault, limited regeneration is still possible, depending upon how high the intake air temperature is and the operating condition of the engine.
Diagnosis
Monitoring of the intercooler bypass flap (by means of the position sensor) includes the following checks:
โข Reference voltage of the position sensor
โข Limit value range check,
โข Plausibility check,
โข Control deviations,
โข Sticking intercooler bypass flap.
Since the EGR system only works to a limited extent in the event of a fault, this is a MIL active component.
Possible diagnostic trouble codes: P022A, P022B, P022C, P024A, P024B, P024E, P024F, P0033, P138C.