PCV Monitoring

9 PCV MONITORING

The PCV system assures that no gas from the crankcase system escapes into the atmosphere. All the information for OBD approval was also presented or send to ARB separate.

9.1 Detection of leak after throttle

Applicable only for test groups






9.1.1 General Description
During operation of reciprocating internal combustion engines, gases escape from the combustion chamber into the crankcase through very small gaps between the piston rings and the cylinder running surfaces. Positive crankcase ventilation (PCV) prevents overpressure build-up in the engine interior and ensures a defined discharge of the blow-by gas. This gas, which contains pollutants and oil, is not discharged into the atmosphere, but conducted to the air intake system through an oil separator and burned. A leak in the return line causes an unintended mixture deviation due to the additionally drawn in fresh air.
This monitor only functions in combination with a load sensor located upstream from the positive crankcase ventilation system.

9.1.2 Leak after the Throttle, P2279

Monitoring Strategy
For detecting a leak after the throttle, a parameter is monitored which is calculated from the averaged lambda control value with correction factors and the current lambda deviation.

Typical Enable Conditions
- Time since engine start > threshold value
- Engine load < threshold value
- Mass air flow < threshold value
- Engine coolant temperature > threshold value
- Intake air temperature < threshold value
- Lambda control value > threshold value and lambda control active (controller must not be "stuck" at the control maximum stop)
- Lambda setpoint value in defined range
- Vehicle speed < threshold value (engine speed close to idle)
- Altitude < threshold value

Malfunction Criteria
A leak after the throttle results in a mixture deviation which is detected by the lambda control. From the averaged lambda control value a parameter for detecting a leak after the throttle is calculated through mixture adaptation factors and the current lambda deviation. If this parameter is greater than a threshold value, a time counter is incremented as long as this condition persists. If the parameter is less than a threshold value, a second time counter is incremented as long as that condition persists. The difference between the two time counters is calculated and divided by the total measurement period. If this value is greater than a threshold value, a fault counter is incremented. If the fault counter is greater than a threshold value, the fault "leak after the throttle" is detected.






9.2 Detection of an air leak in the intake manifold

Applicable only for test groups






9.2.1 General Description
In order to achieve optimum engine operation regarding torque requirements and exhaust-gas emissions, the air mass that enters the combustion chamber during one combustion cycle must be measured precisely. The measured mass air flow is proportional to the molar mass of the oxygen contained in it, and it is used to determine the molar oxygen mass available per cylinder charge. On the basis of this mass air flow the fuel quantity required to be injected for an optimum combustion is determined.
The primary load signal from the MAP sensor is adapted with a modeled secondary load signal to compensate for air leaks in the engine operating range close to idle speed.

9.2.2 Air Leak in the Intake System, P2279

Monitoring Strategy
The adaptation value of the MAP sensor is continuously monitored. If this adaptation value exceeds a defined threshold value, an air leak in the intake manifold is detected.

Typical Enable Conditions
- Setpoint mass air flow is in a defined range
- Engine temperature in a defined range
- Ambient pressure greater than a defined threshold value

Malfunction Criteria
The mass air flow used by the engine is determined with a pressure sensor in the intake manifold. Simultaneously, a mass air flow model is calculated from the throttle position and the engine speed. An adaptation value is continuously calculated from the difference between the measured mass air flow (primary load signal based on MAP Sensor) and the modeled mass air flow (secondary load signal based on throttle position and engine speed) The difference itself is used as a correction factor for "fast mass air flow correction". The adaptation value is used to compensate for air leaks in the engine operating range close to idle speed.

If the intake manifold has a leak, the measured mass air flow differentiates to the modeled mass air flow mainly in the engine operating range close to idle speed. If the adaptation value is greater than a defined threshold value for a defined time period, an air leak in the intake manifold is detected. A corresponding fault is then stored in the fault memory if, additionally, the correction factor from the "fast mass air flow correction" is greater than a defined lower threshold value at the time of the fault detection.