Possible Causes
WARNING: This page is about a different car, the 2003 Mazda B4000, 2003 Mazda B3000, and 2003 Mazda B2300. However, it is still accessible from the selected car via links, so may be relevant.
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.