Possible causes:
- Faulty Oxygen Sensor (Bank 1, Sensor 1)
- Oxygen Sensor harness is open or shorted
- Fuel pressure/regulator problem
- Intake air leak
- Mass Air Flow (MAF) sensor problem
- Faulty fuel injector on Cylinder 1
- Engine Coolant Temperature (ECT) sensor failure
- Insufficient Fuel System Pressure
- Engine mechanical condition
- PCM failure