Test Group XBMXV02.5M52 & XBMXV02.8M52

WARNING: This page does not describe the selected car, but rather 14 other vehicles, including the 1999 BMW Z3, 1999 BMW M3, 1999 BMW M Roadster, 1999 BMW M Coupe, and 1999 BMW 750iL. However, it is still accessible from the selected car via links, so may be relevant.

General Description - Catalyst monitoring is based on monitoring its oxygen storage capability. Engine closed loop feedback control generates lambda (air/fuel ratio) oscillations in exhaust gas. These oscillations are dampened by oxygen storage activity of catalyst. Amplitude of remaining lambda oscillations downstream of catalyst indicates storage capability. See Fig 1-Fig 3 .

Monitoring Procedure - Conversion efficiency of both catalyst systems (Cyls. 1-3 and 4-6) are separately monitored. To determine efficiency, lean and rich time periods of oxygen sensors both up and downstream will be compared. Smaller of two ratios determined is used for further processing. Cycle counter is incriminated by one count after each cycle. If counter reaches a predetermined number of checks and sum of all ratios determined is greater than a fixed value, a fault will be stored in computer memory. Monitoring procedure is then terminated until engine is shut-off and started again.

Fig 1: Monitoring Oxygen Sensor Efficiency

Courtesy of BMW OF NORTH AMERICA, INC.

Fig 2: Catalyst Monitoring Structure Flow Chart

Courtesy of BMW OF NORTH AMERICA, INC.

Fig 3: Catalyst Monitoring System Operation Diagram

Courtesy of BMW OF NORTH AMERICA, INC.