1.6.3.1 Monitoring Function

The fuel system diagnosis uses two different monitors. The first one evaluates the percentage of the long term fuel adaptation. The other monitor evaluates the percentage of the short term fuel trim's physical limits.

The short term fuel trim monitoring is active in every engine state, except for the deceleration fuel cut-off state. The long term fuel trim evaluation is active during its learning process, but is not active during the canister purge phases of the EVAP system. Therefore, an additional learning process can be initiated and the evaluation can run when large deviations are present in the short term fuel trim. When the enable conditions are met, different counters are started for both evaluations. When no condition is present, the end diagnostic counter decrements to zero from a calibrated value and a passing decision is made.

When a lean condition is present and the total fuel control exceeds the upper calibrated threshold, two timers are started. When the lean threshold counter exceeds the calibrated threshold before the reset timer has decremented to zero from a calibrated threshold, a lean error is set.

When a rich condition is present and the total fuel control exceeds the lower calibrated threshold, two timers are started. When the rich threshold counter exceeds the calibrated threshold before the reset timer has decremented to zero from a calibrated threshold, a rich error is set.

The time counters are increased when the "lambda controller" or the "lambda adaptation" exceed their respective minimum or maximum thresholds.

The error is detected as soon as one of the time counters reaches its respective maximum value.