Fuel System Description/Monitoring Procedure

As fuel system components age or otherwise change over the life of the vehicle, the adaptive fuel strategy learns deviations from stoichiometry while running in closed loop fuel.

These learned corrections are stored in keep alive memory as long term fuel trim corrections. They continue to be changed and stored until they exceed normal limit or if a malfunction occurs, the long term fuel trim values will reach a rich or lean limit where the adaptive fuel strategy is no longer allowed to compensate for additional fuel system changes.

Long term fuel trim corrections at their limits, in conjunction with a deviation in short term fuel trim, indicate a rich or lean fuel system malfunction.