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Home >> Subaru >> 2017 >> Legacy 2.5i Limited >> Repair and Diagnosis >> External Pages >> Different variant/trim >> Section 14 (Engine Control System (Diagnostics) (P0161 To P0685) (H6DO)) >> Diagnostic Procedure with Diagnostic Trouble Code (DTC) >> DTC P0420 Catalyst System Efficiency Below Threshold Bank 1 >> Diagnostic Method

Diagnostic Method

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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.

JUDGMENT VALUE SPECIFICATION

Malfunction Criteria Threshold Value
Rear oxygen sensor output voltage deviation sum value/front oxygen (A/F) sensor lambda deviation sum value (bank 1) > 7

Time needed for diagnosis:  30 - 55 seconds

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