Possible Causes
WARNING: This page is about a different car, the 2003 Mazda Protege5 and 2003 Mazda Protege. However, it is still accessible from the selected car via links, so may be relevant.
- Engine malfunction.
- Exhaust system leak.
- Front HO2S deterioration.
- Front HO2S heater malfunction.
- Low engine compression.
- Open or short circuit between front HO2S and PCM.