DTC P2177-00: System Too Lean Off Idle Bank 1: General Description

ECM uses a closed loop air/fuel metering system. The ECM monitors all vehicle HO2S signal voltages to control fuel delivery. Fuel delivery is controlled only when in closed loop operation. When fuel is added, the HO2S will increase its voltage signal. When the ECM sees the HO2S voltage increase passed a calculated point, fuel delivery will be reduced. The ECM will increase and decrease fuel delivery to keep the HO2S crossing 500 mV, and air fuel mixture near 14.7:1.

The ECM monitors the overall changes in fuel delivery by looking at the long-term and the short-term fuel trim values. The ideal fuel trim value is around 0%. The ECM will add fuel when the HO2S signal is indicating a lean condition (below 0%). ECM will reduce fuel delivery when fuel trim is above 0%. The DTC relevant to fuel trim will be set when the amount reaches excessive levels because of a lean or rich condition trend.