Possible Causes

Possible causes are:

Fuel System

• Contaminated fuel injector(s).
• Excessive fuel pressure.
• Leaking fuel injector(s).
• Leaking fuel pressure regulator.
• Low fuel pressure or running out of fuel.

Induction System

• Air leaks after Mass Airflow (MAF) sensor.
• Improperly seated engine oil dipstick.
• PCV system.
• Vacuum leaks.

EGR System

• Leaking gasket.
• Stuck open EGR valve.

Base Engine

• Cam timing.
• Cylinder compression.
• Engine oil overfill.
• Exhaust leaks before or near HO2S.
• Leaking diaphragm.

Electrical

• Damaged HO2S.
• Damaged PCM.
• Open or shorted HO2S.
• Short to VPWR in harness or HO2S.
• Water in harness connector.