Subaru 2009 IMPREZA Service Manual page 773

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Diagnostic Trouble Code (DTC) Detecting Criteria

GENERAL DESCRIPTION

AD:DTC P0133 O2 SENSOR CIRCUIT SLOW RESPONSE (BANK 1 SENSOR 1)

1. OUTLINE OF DIAGNOSIS

Detect the slow response of front oxygen (A/F) sensor.

Front oxygen (A/F) sensor cover has some ventilation holes for exhaust gas. Clogged ventilation holes are

When the holes are clogged, the A/F output variation becomes slow comparing with the actual A/F variation

because oxygen which reaches the zirconia layer is insufficient. Therefore, if the sensor cover holes are

clogged, the rich to lean judgement in the ECM is delayed when the actual change from rich to lean occurs.

Judge as NG when the actual movement in comparison to the ECM control amount is slow.