Detection Condition

• DTC P0171 indicates air/fuel ratio is too lean (Bank 1).
• DTC P0174 indicates air/fuel ratio is too lean (Bank 2).

Fuel control system uses fuel trim tables stored in PCM to compensate for variances in fuel system components from wear and aging. The fuel trim strategy learns deviations during closed-loop engine operation. Fuel trim has 2 means of adapting; a long term fuel trim and a short term fuel trim. Inputs from Engine Coolant Temperature (ECT), Cylinder Head Temperature (CHT) and Mass Airflow/Intake Air Temperature (MAF/IAT) sensors are required to activate fuel trim adjustments. The HO2S detects presence of oxygen in exhaust and provides PCM with feedback identifying air/fuel ratio. A fuel trim factor is added to fuel injector pulse width calculation according to long and short term fuel trims. Long term fuel trim values at their rich or lean limits indicate a fuel system malfunction.