Intake air leak
Faulty O2 Sensor
Faulty Mass Air Flow (MAF) Sensor
O2 Sensor harness is open or shorted
O2 Sensor circuit poor electrical connection
Engine Light ON (or Service Engine Soon Warning Light)
This fault code is stored in the Engine Control Module (ECM) when the ECM is no longer capable of controlling the air-fuel ratio. For the correct operation of the catalytic converter, the ECM is required to keep the Air-Fuel Ratio (AFR) at approximately lambda 1; this equates to an AFR of 14.7:1 by mass. This is achieved by trimming the fuel mixture to the required amount to cater for slight anomalies during normal operating conditions. However, when a fault causes the fuel trim to exceed a predetermined level the malfunction indicator light is illuminated and a limited operating strategy is employed. The pre-catalyst exhaust gas oxygen sensor is the primary component used for calculating the fuel trim once the system enters closed-loop control. The fuel trim data can be displayed as a percentage, either positive or negative.
This Diagnostic Trouble Code (DTC) can be caused by a faulty mass airflow sensor, fuel pressure regulator, fuel pump, exhaust or intake leaks, secondary air injection leaks, or vacuum leaks. Additionally, any mechanical faults can cause this DTC as well. Common failure points associated with this code are a damaged EVAP purge regulator valve, brake booster, and hoses, electric vacuum pump (if equipped), PVC or ventilation system.