Adaptive Fuel Function

Rich
If during steady state driving the fuel system continually indicates a total air fuel ratio (FAR) closed-loop compensation value below a set failure limit, the purge valve will be closed. This strategy includes long term adaptions. Should the value remain below the failure threshold the fuel system is judged to have failed rich.

Lean
Should the AFR closed-loop compensation stay above the set failure limit for too long the fuel system will be judged to have failed lean

For both rich and lean diagnostics the relevant DTC is stored if the failure judgement is made on two successive trips.

NOTE: The fuel system judgements are also used to perform the upstream oxygen sensor low voltage diagnostics, see Oxygen Sensor.