Diagnostic Method 1

Detect the malfunction depending on the average value of time necessary for λ to inverse the air fuel ratio from "Lean → Rich → Lean" to "Rich → Lean → Rich".

Fig 1: Front Oxygen Sensor Signal Lean To Rich Graph

Courtesy of SUBARU OF AMERICA, INC.

Judge as NG when the following conditions are established.

JUDGMENT VALUE SPECIFICATION

Malfunction Criteria	Threshold Value	DTC
Average value of time necessary for λ to inverse the air fuel ratio to Lean → Rich → Lean	> 80 ms	P015A
and
Average value when λ is lean	> 10 ms
Average value of time necessary for λ to inverse the air fuel ratio to Rich → Lean → Rich	> 130 ms	P015B
and
Average value when λ is rich	> 300 ms

Time needed for diagnosis: 70000 ms

Malfunction indicator light illumination: Illuminates when malfunction occurs in 2 continuous driving cycles.