Thought the following might help the discussion a little bit. All of this is taken from "BMW Advanced Diesel Technology" dated September 2008.
Quote:
Crankcase Vent
The crankcase vent in the US version is heated. In addition, the
operation of the crankcase breather is OBD monitored. This is
because a leaking system would increase unwanted emissions.
The only probable reason for a leak in the system would be that the
blow-by pipe is not connected to the cylinder head cover. In order
to facilitate protection of this situation by the OBD, the heating line
is routed via a connector to the cylinder head cover (2).
Essentially, this connector serves only as a bridge so that actuation
of the heating system is looped through. The plug connection is
designed in such a way that correct contact is made only when the
blow-by pipe has been connected correctly to the cylinder head
cover, i.e. the contact for the heating system is not closed if the
blow-by pipe is not connected to the cylinder head cover. The
OBD system recognizes this situation as a fault.
Note: If the blow-by pipe is not connected to the cylinder
head correctly, the OBD will activate theMIL
(Malfunction Indicator Lamp).
Note:
When making repairs which concern malfunctions of the
crankcase ventilation system. Or, if any repairs are made to a
turbocharger which has leaked oil into the engine, be sure to
remove any residual oil in the intake air system.
Failure to do so may result in an engine over-rev situation
causing irreparable engine damage. In this case, the warranty
may be affected.
High Pressure EGR Valve
Compared to the European version, the high pressure EGR is
equipped with the following special features:
• Electric EGR valve with positional feedback
• Temperature sensor before high pressure EGR valve
• EGR cooler with bypass.
The electric actuating system of the EGR valve enables exact
metering of the recirculated exhaust gas quantity. In addition, this
quantity is no longer calculated based solely on the signals from
the hot-film air mass meter and oxygen sensor but the following
signals are also used:
• Travel of high pressure EGR valve
• Temperature before high pressure EGR valve
• Pressure difference between exhaust gas pressure in the
exhaust manifold and boost pressure in the intake manifold.
This enables even more exact control of the EGR rate.
The EGR cooler serves the purpose of increasing the efficiency of
the EGR system. However, reaching the operating temperature as
fast as possible has priority at low engine temperatures.
In this case, the EGR cooler can be bypassed in order to heat up
the combustion chamber faster. For this purpose, there is a bypass
that diverts the flow of the exhaust around the EGR cooler.
This bypass is actuated by a flap which, in turn, is operated by a
vacuum unit. The bypass is either only in the "Open" or "Closed"
position.
|