Circuit/System Verification

IMPORTANT: Disregard any transmission symptoms, antilock brake system (ABS) indicators, and traction control system (TCS) indicators until any fuel trim faults are repaired. A fuel trim fault may cause default actions such as harsh shifts and illumination of the ABS/TCS indicators.

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.
- If the value does not vary from approximately 40 mV to approximately 900 mV, refer to DTC P0131, P0132 or P0134 , DTC P0133, P1133, or P2A00 , DTC P0030, P0053, or P0135 , DTC P0137, P0138, or P0140 , DTC P2A01 , or DTC P0036, P0054, or P0141 .

IMPORTANT: The EVAP purge enablement may cause the FT to be momentarily outside the normal range.

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 moving slowly between +10 percent and -10 percent, with near 0 percent the optimum, with the engine running at operating temperature.