Fuel Trim System Operation

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