Fuel Trim System Operation

The Fuel Trim (FT) system monitors the averages of short-term and long-term FT values. If these FT values stay at their limits for a calibrated period of time, a malfunction is indicated. The FT diagnostic compares the average of short and long-term FT values. If either value is within the thresholds, a pass is recorded. If either value is outside the thresholds, a rich or lean FT DTC will set.