Short Term FT

The scan tool displays 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 voltage. 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 system.

The scan tool displays counts. 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 voltage. When the oxygen sensor voltage remains below 450 mV the PCM adds fuel and the Short Term FT parameter displays a count greater than 128. When the oxygen sensor voltage stays above 450 mV the PCM subtracts fuel and the Short Term FT parameter displays a count less than 128. During an extended idle with high ambient temperatures, the EVAP canister may purge causing the Short Term FT to read lower than 128. This is a normal condition. The fuel trim values at maximum authority may indicate an excessively rich or lean system.