Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
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HOMESERVICE MANUALSCHEVROLET1999METRO L4-079 1.3L VIN 2 MFIREPAIR AND DIAGNOSISPOWERTRAIN MANAGEMENTCOMPUTERS AND CONTROL SYSTEMSTESTING AND INSPECTIONSCAN TOOL TESTING AND PROCEDURESSCAN TOOL DATA DEFINITIONS - POWERTRAIN SYSTEMSSHORT TERM FT
1999 Chevrolet Metro L4-079 1.3L VIN 2 MFI
Short Term FT
1999 Chevrolet Metro L4-079 1.3L VIN 2 MFISECTION 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.
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.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.