Circuit/System Verification

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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.

For E85 compatible engines only-Over estimation of the ethanol content will result in a rich shift of fuel trim values, and under estimation will result in a lean shift of fuel trim values. A fuel trim DTC may set if the learned alcohol content, Fuel Alcohol Content parameter on the scan tool, is different than the measured alcohol content in the vehicle such that the fuel trim values exceed failure threshold values. Refer to Fuel Composition Diagnosis .

Verify that other DTCs are not set.
- If any DTCs are 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 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, P0137, or P0138 , DTC P0133, P0134, P0140, P1133, P2A00 or P2A01 , DTC P0151, P0152, P0157, or P0158 , or DTC P0153, P0154, P0160, P1153, P2A03, or P2A04 .

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

The normal Short Term FT parameter should be 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.