BMW Cars 1999-06

Positive Crankcase Ventilation (PCV) System


Description & Operation

BMW engines incorporate a pressure controlled Crankcase Ventilation (CV) system. The crankcase ventilation system uses various different crankcase ventilation valves depending on the installed engine type.

Although the valves may look different, their function is similar, using a spring and a diaphragm assembly to control the crankcase pressure. A properly functioning pressure control valve is designed to maintain a slight vacuum of about 0.14-0.20 psi (10-15 mbar) in the crankcase assuring proper crankcase venting during all engine operating conditions.

A malfunctioning crankcase ventilation valve could cause one of the following conditions:

Engine running rough
Whistling noises at the crankcase ventilation valve
Illumination of the Check Engine Light (MIL)
Stored DME faults such as misfire all cylinders or Oxygen Sensor I mixture faults

The crankcase ventilation system is essentially maintenance free. There are no mechanical portions that need to be adjusted, nor are there any parts that need to be replaced on a scheduled basis.

The only checks that can be made to the system is for plugged or cracked hoses and faulty connections. Pull the hoses off the connections and check for plugging. Inspect the hoses for cracking. Check that the hoses are fully seated on the connection points.

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Fig. The basic BMW crankcase ventilation system operation

Diagnosis & Testing

Using Tool No. 99 00 0 001 410 or its equivalent check the crankcase ventilation system as follows:

  1. Follow the instructions included with the slack tube manometer for proper initial tool set up and operating procedures.
  3. Connect the manometer to the engine oil filler neck.
  5. Open the valves approximately 1 / 4 turn, then zero the sliding scale.
  7. The manometer should indicate a slight vacuum (about 5 inches of water).
  9. If the vacuum is too high, check for a damaged diaphragm and replace as necessary.

A higher than normal crankcase vacuum may cause the crankshaft seals to leak atmospheric air into the crankcase when the engine is operated. Should this occur, a whistling and/or howling noise can be heard from the seal areas.

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Fig. Unplug the hoses and check for blockages and cracked hoses-M50 engine

Removal & Installation

Except M42 And M44 Engines
  1. Remove the valve assembly from the fitting on the cam cover and disconnect the two breather hoses.
  3. Installation is the reverse of the removal procedure.

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Fig. Crankcase ventilation connector-M50 engine

M42 And M44 Engines
  1. Refer to the upper intake manifold removal procedure in Section 3 and remove the upper intake manifold.
  3. Place a drain pan under the engine, clamp off the two coolant lines and disconnect.
  5. Remove the breather hose from the diaphragm assembly.
  7. Installation is the reverse of the removal procedure.

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Fig. The crankcase ventilation system on M42 and M44 engines is mounted between the upper and lower intake manifold

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Fig. The ventilation system on M42/M44 engines has a diaphragm assembly and an engine coolant passage