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Home >> Subaru >> 2017 >> Outback 2.5i >> Repair and Diagnosis (Single Page) >> Engine Performance >> System >> Engine Control System (Diagnostics) (P0171 To P0685) (H4DO) >> Diagnostic Procedure with Diagnostic Trouble Code (DTC) >> DTC P0420: Catalyst System Efficiency Below Threshold Bank 1 >> Diagnostic Method

Diagnostic Method

After the enable conditions have been established, calculate the front oxygen (A/F) sensor lambda deviation sum value and the rear oxygen sensor output voltage deviation sum value in every 32 ms x 4 times. If the front oxygen (A/F) sensor lambda deviation sum value is the predetermined value or more, calculate the diagnostic value.

If the duration of time while the following conditions are met is within the time indicated, judge as NG. Except for PZEV model

JUDGMENT VALUE SPECIFICATION

Malfunction Criteria Threshold Value
Rear oxygen sensor output voltage deviation sum value - front oxygen (A/F) sensor lambda deviation sum value > 8

PZEV model

JUDGMENT VALUE SPECIFICATION

Malfunction Criteria Threshold Value
Catalyst monitoring value - Rear oxygen sensor response compensation coefficient > 0.35 g
Fig 1: Catalytic Converter Monitor Value
G11583399Courtesy of SUBARU OF AMERICA, INC.

Map 

Estimated catalyst temperature °C (°F) 450 (842) 500 (932) 600 (1, 112) 650 (1, 202) 700 (1, 292) 800 (1, 472) 900 (1, 652) 1000 (1, 832)
Temperature factor 1.15 1.1 1 1.15 1.2 1.2 1.2 1.2

* After 5 to 15 seconds of fuel cut recovery, the catalyst monitoring value will be calculated until the rear oxygen sensor exceeds 0.2 V.

Time needed for diagnosis: 

Except for PZEV model: Less than 30 to 55 seconds

PZEV model: Less than 1 second

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