Long Term FT

The scan tool displays percentage. The PCM derives the Long Term Fuel Trim from the Short Term Fuel Trim value. The Long Term Fuel Trim represents a long term correction of fuel delivery. A value of 0 percent indicates that fuel delivery requires no compensation in order to maintain the PCM commanded air/fuel ratio. A negative value significantly below 0 percent indicates that the fuel system is rich and the PCM is reducing the fuel delivery (decreased injector pulse width). A positive value significantly more than 0 percent indicates that a lean condition exists and the PCM compensates by adding fuel (increased injector pulse width). Fuel trim values at maximum authority may indicate an excessively rich or lean system.