Possible Causes
- Engine misfire.
- HO2S disconnected.
- HO2S mechanical damage.
- HO2S to ECM wiring fault.
- HO2S short circuit to ground.
- HO2S to ECM variable current circuit shielding open.
- HO2S heater circuit fault.
- Exhaust leak.
- Low exhaust temperature.
- Injector flow partially blocked.
- Catalyst efficiency decrease.
- HO2S failure.