Diagnostic Overview / Monitoring Function
(P0171, 172,174, 175)
The ECM monitors the fuel system control continuously during all engine states except PUC (decal fuel cut-off). After the enable conditions are met a counter is started. At this point the ECM evaluates the total percentage of short and long term fuel control. If no condition is present the end diagnostic counter will decrement from a calibrated value to zero and a passing decision is made.
If a lean condition is present and total fuel control is above the calibrated threshold two timers are started. If the lean threshold counter exceeds the calibrated threshold before the reset timer has decremented from a calibrated threshold to zero a lean error is set.
If a rich condition is present and total fuel control is below the calibrated threshold two timers are started. If the rich threshold counter exceeds the calibrated threshold before the reset timer has decremented from a calibrated threshold to zero a rich error is set.
The time counter is increased while "lambda controller + lambda adaptation" exceed minimum or maximum threshold.
The error is detected as soon as the time counter reaches its maximum value.