The ECU has run out of range in adapting the mixture in reference to the O2 Sensor signal (multiplicative adaptation) and/or in reference to the engine running conditions (additive adaptation).
Possible causes:
- Engine Temperature sensor/circuit defective, but the signal still in realistic range.
- Fuel Pressure incorrect
- Fuel Injector(s) leaking
- Fuel Injectors clogged
- Incomplete combustion (ignition or compression problem, excess O2 in the exhaust)
- Vacuum leak (lean mixture)
- Oxygen Sensor defective or contaminated with silica (Voltage change extremely slow)
- Exhaust system leak upstream of the O2 Sensor (stray air brings extra O2 making the mixture to appear lean)
- Fuel Evaporation Control system defective
- vehicle driven out of fuel (tank empty)
The reason for this fault is that ECU has received very high signal from the sensor. The fault is present now. Take appropriate action to fix this sensor fault. Dashboard warning light was activated for this fault.