2003 3BMXV06.0N73
WARNING: This page is about a different car, the 2003 BMW 760Li, 2003 BMW 745i, and 2003 BMW 745Li. However, it is still accessible from the selected car via links, so may be relevant.
- General Description -
Catalyst monitor is based on determining oxygen storage capability. Nonlinear correlation between conversion efficiency and storage capability has been shown in various investigations. Catalyst is diagnosed by comparing its storage capability against storage capability of a borderline catalyst. Oxygen storage capability can be determined by one of the following 2 methods:
- Oxygen Reduction After Fuel Cut Off (Passive Test) - During fuel cut off, oxygen is stored in catalyst. After fuel cut, catalyst is operated with a rich A/F ratio and amount of removed oxygen is determined. If this passive test indicates an oxygen storage capability highly above borderline catalyst, catalyst is diagnosed without an error, otherwise monitor will be restarted after next fuel cut off.
- Oxygen Filling (Active Test) - First, a mixture with a low A/F ratio is put through catalyst until any oxygen has been removed. Then, catalyst is operated with a high A/F ratio. Oxygen Storage Capability (OSC) is calculated out of oxygen mass stored in catalyst. Catalyst is operated in this mode until oxygen stored in catalyst exceeds a calibrated limit or downstream oxygen sensor indicates catalyst is completely saturated with oxygen. Catalyst is then diagnosed by comparing its oxygen storage capability to calibrated threshold of a borderline catalyst. See Figure.
- Monitoring Structure -
According to operating principle described above, following main parts of monitor can be distinguished:
- Monitoring amount of removed oxygen after fuel cut off.
- Check of monitoring conditions for active test.
- Lambda request (interface to lambda control).
- Mixture enrichment in order to remove any stored oxygen.
- Measurement of Oxygen Storage Capacity (OSC) by lean A/F ratio operation.
- Fault detection. See Figure.
- Oxygen Removal After Fuel Cut Off - During fuel cut off, catalyst is completely filled with oxygen. If amount of rich gas required to remove this oxygen exceeds a threshold, a good catalyst will be notified.
- Check Of Monitoring Conditions For Active Test - Diagnostic principle uses precise measurement of A/F ratio fed into catalyst. This requires verification if engine runs in acceptable operating conditions. If such operating conditions are not present anymore, monitor is terminated and restarted only sometime later.
- Lambda Request - Requested A/F ratio (rich or lean) is commanded from monitor through mixture control.
- Mixture Enrichment - Low A/F ratio (lambda less than one) is applied in order to remove any stored oxygen from catalyst.
- Measurement Of Oxygen Storage Capacity - After MIXTURE ENRICHMENT, a high A/F ratio (lambda greater than one) is fed into catalyst. Oxygen mass absorbed by catalyst is determined according to signal of upstream lambda sensor. A lean mixture will be requested until either downstream lambda sensor indicates catalyst to be completely saturated with oxygen, or stored oxygen mass exceeds threshold OSC of borderline catalyst.
- Fault Detection -
Monitor finishes without an error if passive test detects a storage capability highly above borderline limit. If passive test does not meet condition for a good catalyst, active test is initiated and OSC is calculated. Catalyst is diagnosed by comparing determined OSC against borderline threshold. Monitoring conditions for active test include:
- No error on lambda sensors (signal, aging, heater).
- Canister purge value less than limit.
- No error on EGR system (if available).
- Modeled catalyst temperature within range.
- Misfire rate less than limit.
- Regular A/F control (no fuel cut off).
- Engine mass airflow within range. See Figure.