General Information

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





Signal Waveform & Data