Long Term FT

Scan tool displays -25 - +20 percent. Long Term Fuel Trim is derived from the Short Term Fuel Trim value and 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-to-fuel ratio. A negative value significantly below 0 percent indicates that the fuel system is rich and the fuel delivery is being reduced. This condition is represented by a decreased injector pulse width. A positive value significantly more than 0 percent indicates that a lean condition exists and the PCM is compensating by adding fuel. This represents an increased injector pulse width. Because Long Term Fuel Trim tends to follow Short Term Fuel Trim, a value in the negative range due to canister purge at idle should not be considered unusual. The maximum authority of the PCM to control long term fuel trim allows a range of -27 - +27 percent. Fuel trim values at or near the maximum authority may indicate an excessively rich or lean system.