DTC Detection Logic

The ECM monitors the phase gap between heated oxygen sensor 2 signal and heated oxygen sensor 3 signal.

The phase gap between heated oxygen sensor 2 signal and heated oxygen sensor 3 signal becomes small as the HC adsorption catalyst (under floor) is deteriorated.

When the phase gap between heated oxygen sensor 2 signal and heated oxygen sensor 3 signal approaches a specified limit value, the HC adsorption catalyst (under floor) malfunction is diagnosed.

Fig 1: HC Adsorption Catalyst Function Chart

Courtesy of NISSAN MOTOR CO., U.S.A.

DTC DETECTING CONDITION REFERENCE CHART

DTC No.	Trouble diagnosis name	DTC detecting condition	Possible cause
P2423	HC adsorption catalyst efficiency below threshold	HC adsorption catalyst (under floor) does not operate properly. HC adsorption catalyst (under floor) does not have enough oxygen storage capacity.	HC adsorption catalyst (under floor) Exhaust tube Intake air leaks Fuel injector Fuel injector leaks Spark plug Improper ignition timing