Fuel Trim Cell Diagnostic Weights

No fuel trim DTC will set regardless of fuel trim counts in cell "0" unless the fuel trim counts in weighted cells are also outside specifications. This means that vehicle could have a fuel trim problem causing a problem under certain conditions (i.e., engine idle high due to a small vacuum leak or rough due to a large vacuum leak) while it operates fine at other times. No fuel trim DTC would set (although an engine idle speed DTC or Heated Oxygen Sensor DTC may set). Use scan tool to observe fuel trim counts while problem is occurring.