Tank System

OBD II functions

Function
The following summary describes the OBD-II functionality for the R50 and the R53.

Ignition misfiring detection
This diagnosis monitors the engine for misfires. If misfiring is detected, the cylinders responsible are established. There is a malfunction when misfiring occurs within the monitoring limits. If a certain rate is exceeded, these misfires will damage the catalytic converter and the exhaust emissions will be increased.

The prerequisite for reliable misfire monitoring is a precise segment measurement (180� for 4-cylinder engines). The calculated irregular operation is compared to the limit values that depend on the engine speed and the engine load. Each cylinder is analyzed individually.

Fuel system diagnosis
Various fuel system problems can occur and affect the exhaust emissions in different ways. For example:

- Low pressure hose of the fuel-pressure regulator disconnected. This can lead to exhaust emission problems. However, due to the homogeneous mixture, it has no influence on the catalytic converter.

- Cylinder distribution problems due to injection valve failure. This affects the catalytic converter as the mixture is not homogeneous. In general, this means that the volume of exhaust gas to be reduced increases, leading to a reduction in efficiency.

Pre-catalytic converter Lambda oxygen sensor diagnosis
The functional characteristics of the pre-catalytic converter Lambda oxygen sensor are monitored to meet the legal requirements for OBD-II.

The pre-catalytic converter Lambda oxygen sensor causes an increase in exhaust emissions if the response time is reduced too strongly or the fuel-air ratio in the closed regulating circuit is too far away from the efficiency window of the catalytic converter.

A malfunction is indicated if the adaptive values of the Lambda control function lie outside the specified limits.

Catalytic converter monitoring
This monitoring function checks the efficiency of the catalytic converter within the OBD-II requirements. The post-catalytic converter Lambda oxygen sensor indirectly calculates the efficiency of the exhaust emission reduction. This calculation is possible as a result of monitoring the post-catalytic converter Lambda sensor activity. If the efficiency of the catalytic converter is reduced, the activity of the post-catalytic converter Lambda oxygen sensor increases accordingly.

Coolant thermostat monitoring
This function is used to monitor the coolant thermostat for jamming. This could cause higher exhaust emissions because the engine does not reach its normal operating temperature.

Tank system monitoring
This monitoring function uses a leakage-diagnosis pump (LDP) to pinpoint a jamming tank ventilation valve or leakage. The LDP is an electrically actuated or pressure actuated device. This device generates overpressure in the tank system to detect leakage and check the function.