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Home >> Subaru >> 2017 >> WRX STI >> Repair and Diagnosis (Single Page) >> Engine Performance >> System >> Engine Control System (Diagnostics) (P0171 To P0685) (2.5L) >> Diagnostic Procedure with Diagnostic Trouble Code (DTC) >> DTC P0420 Catalyst System Efficiency Below Threshold Bank 1 >> Execution Condition
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Execution Condition

Secondary parameters Execution condition
Battery voltage ≥ 10.9 V
Barometric pressure ≥ 75.1 kPa (563 mmHg, 22.2 inHg)
Sub feedback In operation
Amount of intake air ≥ 10 g/s (0.35 oz/s)
and
< 50 g/s (1.76 oz/s)
Estimated catalyst temperature ≥ 450 °C (842 °F)
Vehicle speed ≥ 40 km/h (24.9 MPH)
Rear oxygen output change from 0.55 V or less to 0.55 V or more Experienced after fuel cut
Estimated temperature of the rear oxygen sensor element ≥ 500 °C (932 °F)