Circuit/System Verification

IMPORTANT: If any DTCs other than DTC P0171 or P0172 are also set, refer to Diagnostic Trouble Code (DTC) List - Vehicle .

Allow the engine to reach operating temperature. With the engine running, observe the HO2S parameter with a scan tool. The HO2S 1 value should vary from approximately 40 mV to approximately 900 mV, and respond to fueling changes.
The normal Short Term FT parameter should be moving rapidly between +10 percent and -10 percent, with near 0 percent the optimum, with the engine running at operating temperature.
The Long Term FT parameter should be between +10 percent and -10 percent, with near 0 percent the optimum, with the engine running at operating temperature. A larger negative value may be present if EVAP purge is enabled.