Short Term FT-1

The scan tool display is a positive or negative percentage. The Short Term Fuel Trim (FT) represents a short term correction to fuel delivery by the PCM. The Short Term FT correction is driven by the fuel control oxygen sensor. When the oxygen sensor voltage remains below 450 mV the PCM adds fuel and the Short Term FT parameter displays a positive percentage. When the oxygen sensor voltage stays above 450 mV the PCM subtracts fuel and the Short Term FT parameter displays a negative percentage. During an extended idle with high ambient temperatures, the EVAP canister may purge, causing the Short Term FT to read in the negative range. This is a normal condition. The fuel trim values at maximum authority may indicate an excessively rich or lean condition.