Test Groups 1BMXV04.4LEV & 1BMXT04.4E53
General Description - At cold start, secondary air pump and valve are switched on for their normal operating function. Secondary air delivered into exhaust gas causes a lean mixture indicated by output voltage of oxygen sensor. Anytime oxygen sensor indicates a rich mixture (voltage greater than a fixed limit) within a predetermined time range and calculation of relative secondary air mass is less than a defined threshold, secondary air system appears to be faulty. Now a correction procedure follows immediately, after secondary air system is switched off. Air/fuel influence is determined by deviation of lambda controller.
If influence is less than a fixed threshold, finally a fault will be detected. If influence is greater than a fixed threshold, results of diagnosis will be rejected as long as a lean mixture (voltage less than a fixed limit) is indicated from oxygen sensor within a predetermined time range and correction of air/fuel influence (after secondary air pump shuts-off) is less than a fixed threshold, a fault will also be detected. See Fig 1.