Excessive nitrogen oxides (NOx) emission

Perform troubleshooting referring to the following points when ECM has detected no DTC and no abnormality has been found in Visual Inspection:M16A and Engine Basic Inspection:M16A.

Condition	Possible Cause	Action
Excessive nitrogen oxides (NOx) emission	Improper ignition timing	Ignition Timing Inspection:M16A
	Lead contamination of TWC	Check for absence of filler neck restrictor.
	Fuel pressure out of specification	Fuel Pressure Check:M16A
	Faulty closed loop system (A/F feedback compensation) (Poor performance of ECT sensor or MAP sensor)	ECT Sensor Inspection:M16A or MAP Sensor Inspection:M16A
	Faulty electric throttle body assembly	Electric Throttle Body Assembly On-Vehicle Inspection:M16A
	Faulty APP sensor	APP Sensor Inspection:M16A
	Faulty fuel injector	Fuel Injector Circuit Check:M16A or Fuel Injector Inspection:M16A
	Faulty ECM	Inspection of ECM and Its Circuits:M16A
	VVT system out of order	•VVT actuator: VVT Actuator, Camshaft, Tappet and Shim Inspection:M16A •Valve timing: Timing Chain and Chain Tensioner Inspection:M16A •OCV oil circuit: Timing Chain Cover Inspection:M16A