1.6.1.3 Diagnostic Principle

For the engine with crossed exhaust manifold, the air fuel ratio control contains the common known 4-in-1-lambda-control utilizing the measurements of the upstream oxygen sensors and additionally the cylinder balancing function.

Fig 1: Identifying AFR Control Structure For Engine With Crossed Exhaust Manifold

Courtesy of BMW OF NORTH AMERICA, INC.

Since the correction values of lambda control and adaptation are monitored as in the engine with conventional exhaust manifold, this diagnosis monitors particularly faults which are caused by malfunctions at the 'hot end', i.e. after the exhaust manifold. Since reaching the lambda control or adaptation limits is often caused by malfunctions at the 'cold end', additionally fault codes had to be added. The diagnosis for these fault codes monitors the average calculated correction value for each cylinder bank (i.e. cylinders 1-4 and 5-8) using both the exhaust bank-specific adaptation values as well as the cylinder-specific adaptation values.