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Long Term FT
The scan tool range is
-23 to
+16 percent. The long term fuel trim is derived from the short term fuel trim value. This represents a long term correction of the 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 fuel delivery is being reduced, 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, increased injector pulse width. Because long term fuel trim tends to follow short term fuel trim, a value in the negative range due to the canister purge at idle should not be considered unusual. The PCMs maximum authority to control long term fuel trim allows a range between
-23 percent and
+16 percent. Fuel trim values at maximum authority may indicate an excessively rich or lean system.