Test Group YBMXT04.4E53, YBMXT04.453M, YBMXVO4.4LEV, YBMXV04.9S62 & YBMXV05.4LEV
Secondary Air System Monitoring General Description - At cold start the secondary air pump and valve are switched on for their normal operating function. The secondary air delivered into the exhaust gas is causing a lean mixture indicated by the output voltage of the oxygen sensor. Any time the oxygen sensor indicates a rich mixture (voltage greater than a fixed limit) within a predetermined time range and the calculation of the relative secondary air mass is less than a defined threshold, it seems like a faulty secondary air system. Now a correction procedure follows immediately, after the secondary air system is switched off. The air/fuel influence is determined by the deviation of the lambda-controller. If influence is less than a fixed threshold, a fault will be detected. If influence is greater the a fixed threshold, the results of the diagnosis will be rejected. As long as a lean mixture (voltage less than a fixed limit) is indicated from the oxygen sensor, within a predetermined time range and the correction of air/fuel influence (after secondary air pump shuts-off) is less than a fixed threshold, a fault will also be detected. For secondary air system monitoring flow chart, see Fig 1.