Test Group VBM2.8VJGKEK & VBM2.8VJGKFK
WARNING: This page does not describe the selected car, but rather 13 other vehicles, including the 1997 BMW Z3, 1997 BMW 850Ci, 1997 BMW 840Ci, 1997 BMW 750iL, and 1997 BMW 740iL. However, it is still accessible from the selected car via links, so may be relevant.
Catalyst Monitoring General Description - Catalyst monitoring is based on monitoring its oxygen storage capability. The engine closed loop feedback control generates lambda (air/fuel ratio) oscillations in the exhaust gas. These oscillations are dampened by the oxygen storage activity of the catalyst. The amplitude of the remaining lambda oscillations downstream of the catalyst indicates the storage capability.
- Monitoring Procedure - In order to determine the efficiency the lean and rich time periods of the oxygen sensors up and downstream will be compared. See Fig 1. The smaller of the two ratios determined is used for further processing. The cycle counter is incremented by one after each cycle. If the counter reaches a predetermined number of checks (235 lambda controller cycles) and the sum of all ratios determined is greater than a fixed value a fault will be stored in the computer memory. The monitoring procedure is then terminated until the engine is shut-off and started again.
- Monitoring Structure - See Fig 2.
- Block Diagram Of System -
See Fig 3.NOTE: The conversion efficiency of both catalyst systems (Cyl. 1-3 and Cyl. 4-6) are separately monitored.