Intake air leaks
Faulty front heated oxygen sensor
Faulty fuel injectors
Exhaust gas leaks
Incorrect fuel pressure
Lack of fuel
Faulty Mass Air Flow (MAF) sensor
Incorrect Positive Crankcase Ventilation (PCV) hose connection
Engine Light ON (or Service Engine Soon Warning Light)
Excessive Fuel Consumption
With the Air/Fuel Mixture Ratio Self-Learning Control, the actual mixture ratio can be brought closer to the theoretical mixture ratio based on the mixture ratio feedback signal from the heated oxygen sensors 1. The Engine Control Module (ECM) calculates the necessary compensation to correct the offset between the actual and the theoretical ratios.
In case the amount of the compensation value is extremely large (The actual mixture ratio is too lean.), the ECM judges the condition as the fuel injection system malfunction and lights up the Malfunction Indicator Light (MIL) (2 trip detection logic). The Diagnostic Trouble Code (DTC) will be set when the Fuel Injection System does not operate properly, or the amount of mixture ratio compensation is not correct.