General Information

Engine Control

P0171 System too Lean (Bank 1) - General Information

General Description

In order to provide the best possible combination of drivability, fuel economy and emission control, the Powertrain Control Module (PCM) uses a closed loop air/fuel metering system. The PCM monitors the Heated Oxygen Sensor (HO2S) signal voltage and adjusts fuel delivery. Changes in fuel delivery will be indicated by the long-term and the short-term fuel trim values. The ideal fuel trim value is around 0%. The PCM will add fuel when the HO2S signal is indicating a lean condition. Additional fuel is indicated by fuel trim values that are above 0%. The PCM will reduce fuel when the HO2S signal is indicating a rich condition. Reduction in fuel is indicated by fuel trim values that are below 0%. The Diagnostic Trouble Code (DTC) relevant to fuel trim will be set when the fuel trim reaches excessive levels due to a lean or rich condition.

DTC Description

The Powertrain Control Module (PCM) monitors the fuel trim value under the detecting condition. If the average exceeds the limit over a certain period, the PCM will set a P0171 and turns on the Malfunction Indication Lamp (MIL).

DTC Detecting Condition